Dual CV1400 - IC 1113 short circuit

Pykon · 4. Februar 2023

Hello Dual Brothers!

It finally happened - my beloved CV 1400 went out of signal. Nothing. Silence. Nothing more than some silent cracks, sometimes. Checked out main voltages from the schematics and ended up as follows: final stage +/- 31 V OK, system +/- 22,7 V OK but no -15 V at the inputs board (Eingangsimpedanzwandler Platine). Measuring the IC 1113 (RC4195 DN) voltage regulator connections on PCB brought about -0 V at pin 5 (instead of -15 V) and +15 V at pin 7. Both +/- 22,7 V at pins 4 and 8 were OK there. Moreover, there is a short circuit to 0V (chassis) at "-15V" pin 5. Assuming that the voltage regulator failed I desoldered IC 1113 from the inputs board but the short circuit from hole 5 to chassis remains on the PCB. There are several elements on the board suspected of making a short circuit: three capacitors (C1126, C1121, C1121'), three IC's (IC 1110, 1111, 1112) and two transistors (T1113 and T1113'). Access to the inputs board is terrible to call it politely and I used to have a hope that desoldering voltage regulator IC and replacing it will solve the problem. Lucky me that I did a quick short circuit check before soldering another voltage regulator from "spare" CV 1400 There is nothing I could desolder from the inputs PCB without disassembling and disconnecting cinch inputs. Technically I should desolder all the mentioned elements as every one of them can cause short circuit. And here comes the question: maybe someone of you here has come across similar situation, short circuit instead of -15 V at pin 5 of IC 1113 and could suggest me where to begin? Maybe Dual CV 1400 family Eingangsimpedanzwandler has a typical issue like mine. It is possible there was no point of desoldering RC4195 from the board but that was just my first thought. Btw - it seems that neither RC4195 DN nor its replacement is available even in the farthest internet. I do not thing the IC 1113 survived my desoldering or short circuit itself. Purchase would be also safer from taking old IC from spare CV 1400. Me and my Dual will appreciate support of any kind

All The Best,

Mike

wacholder · 4. Februar 2023

Hi Mike !

The RC4195 is quite welknown for killing itself. Most popular reason: the tantalium capacitors at the output pins go bust and short it.

Our fellow briegel (Norbert) found that out years ago and while he disliked the - by then already discontinued - RC4195 he came up with a substitution using the more familiar three-leg regulators 78L15 and 79L15.

Go here:https://www.n-malek.de/11201/11263.html#CV62

Scroll down until you find the chapter about the RC4195 and how to replace it with more common parts.

And replace the tantaliums !

And: The CV1400 has *two* of them. One on the main pre-amp board and another on the input board ...

Pykon · 4. Februar 2023

Hi Peter!

Thank you for your advice! I found some RC4195 on ebay, not cheap, but available from China. Funny that in the service manual Dual mentioned tantalium C1126 as ELYT, same as regular electrolyte ones. And my CV 1400 hac another tantalium one C1125 on the input board, protecting +15V from the RC4195. So I have to replace both and then look for the one on the pre-amp board you mentioned.

Can I replace these tantaliums with regular electrolytic capacitors?

PS. Do you think it is possible that RC4195 may have survived tantaliums short circuit?

All The Best,

Mike

wacholder · 4. Februar 2023

Hi Mike !

Zitat von Pykon

Can I replace these tantaliums with regular electrolytic capacitors?

In this application I would assume you can.

It is essentially a DC-operation, nothing where the absolute capacitor value or its tolerances matters much.

The use of tantaliums - in the "good old days" - saved a little bit of space and sometimes an additional ceramic capacitor in parallel to an electrolytic *in case* it was intended to filter out higher frequencies or small spikes. However the progress in electronics and chemics helped a lot to make nowadays aluminium electronlytics almost as good as these first generation liquid tantalium caps.

*If* you buy a quality brand type - not the cheesiest ones made from Chineesium ...

Zitat von Pykon

PS. Do you think it is possible that RC4195 may have survived tantaliums short circuit?

Hard to predict to be true.

The RC4195 has a sort of short-circuit protection, but it does not work very well. It is more of an overload protection during rush-in, but fails on long-term shorts. Whereas "long term" is a matter of minutes in this case. Hundreds of deads on them tells a bit of a sad story.

And to make things worse: it is a dual voltage regulatror for positive and negative voltage. It does not help, if one part survived - and the other does not.

Zitat von Pykon

I found some RC4195 on ebay, not cheap, but available from China.

Well ... if you are lucky they even work.

These RC4195 are not *that* expensive that they are supected to a big fraud scheme as it happens on more valuable processor, memory or "special" chips like hybrids for intermediate stage or final amplifiers. Rumours claim, that two out of three "Sanyo" labelled Hybrid sold from chinese suppliers is a fake. Sometimes they do even work - for some time and if you don't use them up to the values defined in their spec sheets.

Zitat von Pykon

Funny that in the service manual Dual mentioned tantalium C1126 as ELYT, same as regular electrolyte ones.

Most likely they didn't made up their minds on that during data collection. It is a polarized capacitor - and that tend to be electrolytics. Which is a matter of definition. On the other hand on the non-polarized caps they differ between ceramics and foils for instance.

Let me know how it turns out with your CV1400. I have some in my collection and one of them is a very rare first generation "DIN only".

One is used as "daily driver" on the deskside system in my workshop / storage. I like them quite a lot because - compared to the CV1600 or CV1700 - they are reliable and unpretentious in their technical details. Easy to repair and to maintain ... apart from some grounding flaws and in case you have to remove the input board. You will see it. It is ... well ... awkward to say the least.

Pykon · 5. Februar 2023

Hi Peter,

struggling with the input board, I'm starting to think about speaker relays. The symptoms were as followes:

- no sound after turning the amplifier on low initial volume,

- sound partly appears when increasing the volume (with the volume potentiometer)

- then I can decrease the volume and listen to the music

...it might be a matter of coupling capacitors between the pre-amp board (the one with potentiometers) and the end stage board (with two 4700 uF electrolytes and two vertical alu radiators) if such exist because it is the only one place in the sound path where the current is being volume-dependent. But the most simple idea remains - relais. May I know your opinion in this area? Are these relais available and if not, how to clean them out? Especially their transparent plastic housings seem rather delicate. I thought of several methods: brushing the contacts with a sandpaper (not good - metal filings remain inside), using a specialized spray for contacts or efen drilling a hole in the transparent housings to spray the contacts inside

You mentioned your "DIN - only" Dual amp. I have three CV1400 - two with plastic side panels and the one I am fixing, with wooden side panels. Visually inside and outside it looks like new, untouched unit. And it has a "Johann Kaupa, jun., Wiegersen" service or retail sticker. Love the CV1400 loudness signature sound, warm, pleasing timbre. With Revox BX230 closed boxes it is simply priceless experience.

Will come back with the latest news and appreciate your help,

Mike

FDS · 5. Februar 2023

Hi Mike,

here is another Peter. I solved the problem with the ±15V power supply with an own construction.

I was inspired by this circuit.

This is the result:

For the problem with the relais please read this thread.

I think we can find a solution

wacholder · 5. Februar 2023

Hi Mike !

Zitat von Pykon

struggling with the input board,

I told you, didn't I ?

Zitat von Pykon

I'm starting to think about speaker relays. The symptoms were as followes:

- no sound after turning the amplifier on low initial volume,
- sound partly appears when increasing the volume (with the volume potentiometer)
- then I can decrease the volume and listen to the music

Symptomatically. Yes.

That 1400 on my deskside system also suffers a similar problem - on the left channel at least.

A simple, percussive test may bring clarity. If that effect shows up next time - just give the amp a respectful but noticeable clap on the case or the sides.

If the sound comes up immediately it is positively the relay.

These relays are a bit hard to come by due to their pinout. "Standard relays" are wired differently. You could use a handwiring or an adapter socket. One of our fellows (@ HaJoSto) created one a long time ago. Don't know if he still makes them or has one left, but it is worth asking.

Unsoldering and opening them is possible. The clear cover is latched left and right on the bottom. Using a contact file on the contacts and cleaning them with a contact cleaner and canned air helps for about a year (or two). The filing usually causes a mis-alignment of the opposing contacts, which - over time - causes problems again. But: it is worth trying at least. Better than nothing. Did that on various occasions.

There is however another design flaw in this circuitry.

They were utilizing a CMOS CD4011 as a voltage detector for a delay until the relay comes on.

https://www.hifi-archiv.info/D…/Dual%20CV%201400-004.jpg

This is IC1810. Capacitor C1812 / 4.7µF is charged via R1816 / 1M from the auxiliary supply voltage of 8.9V gained via ~G and a diode.

The CD4011 is a generic NAND-gate and its switchpoint is largely undefined between 1/3 to 2/3 of the supply voltage for Low and High.

This - in return - causes the relay to close / open multiple times and very fast when the 4011 changes signal due to the slightly instable supply voltage. It goes "Bzzzzt - Click" until it finally stays closed. That causes a lot wear on the mechanics and the contacts over time.

When you swap the 4011 against the pin-compatible 4093 and change the 4.7µF C1812 against a 2.2µF you get a far better behaviour.

The 4093 has 4 NAND with Schmitt-Trigger. Means: the voltage on the switchpoint has to go higher to change Low - High at about 2/3rd of the supply, but it has to go down to 1/3rd of the supply to release and change from High-Low. The capacitor change takes care of the different timing and the relay goes "Clack!" and nothing else. With the 4.7µF it takes about 15 - 20 seconds for the relay to come on.

Zitat von Pykon

You mentioned your "DIN - only" Dual amp. I have three CV1400 - two with plastic side panels and the one I am fixing, with wooden side panels. Visually inside and outside it looks like new, untouched unit. And it has a "Johann Kaupa, jun., Wiegersen" service or retail sticker.

Wiegersen is a town some 10 miles southwest from Buxtehude in Lower Saxonia in northern Germany.

https://www.hifi-archiv.info/Dual/cv1400/03.jpg

My "DIN-only" CV1400 has no speaker connectors for bare wires and no RCA-sockets for tuner or phono.

The "wooden" panels (made from compressed wooden chips in fact) have been replaced by plastic ones for the last batch of amplifiers to held the sales price within range. I *think* they came after 1979 when Dual has major problems already.

Hi Mike !

Zitat von FDS

For the problem with the relais please read this thread.
I think we can find a solution

Yes - they covered most of the problems and with other amps as well.

I would also do the 4011-4093 swap. I do it regularly on any CV1400 / 1600 coming in. It really helps.

Pykon · 5. Februar 2023

Dual Peter & Peter

Ich werde euch beiden gleichzeitig antworten.

Ich melde, dass meine Dual CV1400 Maschine Nummer 021995 wieder zum Leben erwacht ist.

And that is all my passive German can produce in writing It seems that miracles happen. I replaced C1125 and C1126 bypass tantalium capacitors for the voltage regulator IC1113 with regular Jamicon electrolytes of 10 uF/63V. One of the blue tantalium heroes had a short circuit despite looking like new. To my surprise the RC4195 survived not only tantalium's short but also heat from unsoldering and soldering back on the inputs board.

But this is not all about good news here. The lazy relays syndrome disapeared. The relais work like new, untouched, come into action with a clean, single click. Seems like it was a matter of a negative 15V power supply problem on the inputs board. But how the - you name what - CV 1400 started working after increasing the volume, no idea. I also tried to take out relays transparent housings but was afraid of using too much force. It rather cannot be done without desoldering relays from the board. Anyway, the unit is fully functional again.

The kindness of the community on this forum is not only impressive, but also simply humanly touching. I do not know of any so supportive space I could compare to this Dual forum.

Thank you and all the best,

Mike

wacholder · 5. Februar 2023

Hi Mike !

Zitat von Pykon

Ich werde euch beiden gleichzeitig antworten.

Ich melde, dass meine Dual CV1400 Maschine Nummer 021995 wieder zum Leben erwacht ist.

As for the electronics: you *did* try it.

And a for the results.

Zitat von Pykon

But how the - you name what - CV 1400 started working after increasing the volume, no idea.

This is a fairly common effect.

The relay contacts close - somehow - but the resistance between the contacts is irregularly high.

If you "pump up the volume" and the amplifier produces a higher voltage at the output the contact resistance gets eliminated.

Looking at the contacts closely reveals that the formerly plain surface has turned into a craterized moon surface. This happens by current erosion, bad shaped / slightly misaligned contacts, oxydation and no firm contact under load / relay flattering. All that ruins the contact surfaces and they have pointual contacts at first surrounded by crud and debris. The higher current / higher voltage "burns" them free and the contact is more substantial ... for the moment.

Zitat von Pykon

I also tried to take out relays transparent housings but was afraid of using too much force. It rather cannot be done without desoldering relays from the board.

Unfortunately - True.

The housings could be levered off somehow, but there is a risk to damage board, relay and surrounding components.

The time you could save with a brute-force method often costs you more time to fix the collateral damages.

A proper, less violent method is the better way on the long run.

Zitat von Pykon

Anyway, the unit is fully functional again.

At least for now.

I am pretty sure that at least the relays will need your attention some time in the past.

I guess you'd switched the unit off and on several time in the past days. That clears the worst spots on the contacts - but the silly turn-on behaviour due to the sub-optimal control circuitry and the over all poor condition of the contacts still remains.

Zitat von Pykon

The kindness of the community on this forum is not only impressive, but also simply humanly touching. I do not know of any so supportive space I could compare to this Dual forum.

We try our best.

Most problems can be solved with some respect, friendlyness and humor. The hardest part is, to track the origin of a malfunction. That *needs* quite a bit of communication. And I - for one - cannot assume that the person asking a question has the same level of expertise or experience or equipment at least. So you *need* to be friendly and relaxed and try to ask the proper questions in return.

"Technical Support" is difficult.

Reminds me: where are you located ?

Pykon · 7. Februar 2023

Hi Peter,

it looks like the relays issue was a "relays" issue indeed. The CV 1400 now starts producing the proper sound very precisely from the lowest volume after turning the unit on - a completely uncommon behavior before fixing the IC 1113 tantalums. The relays, after turning them on, are short as solid wire with zero voltage between contacts even under high signal and output load. My hipothesis is that the shorted blue tantalum cap was not dead short for some time but allowing small current pass through several seconds after turning the amp on.

Technically it is possible with small currents that are unable to burn the cap. The issue was virtually unable to locate as any measurements were made several minutes after plugging the amp in. Contrary to the filtering "Knallfrosch" which in case of shorting burns with flames but there are some 230 V driven. Having said that, I assume I would never locate the inputs board tantalium issue if it did not short completely. For now, the CV 1400 works as it was brought new from the store an hour ago. I just love to look and listen to it. With respect to engineers who created this brand and unit. Engineers are real creators, acting behind the scenes.

I am located in Warsaw, Poland. Funny thing, as this is a German forum - I used to be an automotive journalist for Polish version of Auto Bild. And that for some 22 years. Three months ago, our Ringier Axel Springer bosses decided to close the automotive weekly. We continue with some catalogs and Auto Classic, but the paper print edition of the main title is gone.

Electronics are my hobby and as a hobby I also used to create and produce some own music, it is all at a very modest level but enough to refresh the brain Bringing my Duals back on track is a pleasure, I simply love to fix things and giving them another life. As a teenager, I used to make plenty of electronic circuits based on hardly available hobby kits, but there was not much of theoretical understanding involved in the process. But at least I learned to solder Now try to run some courses on electronics - it seems to work. Fixing takes some time, but this time is well spent. I am rather a measuring guy - never run "let's replace this and that, see if it works" repair process. What I can say - the amount of satisfaction when you spent a week on measurements looking for the one small part to replace is an instant reward.

My CV1400 initially had a funny issue with headphones output. While testing, I immediately recognized a specific "surround" effect occurring when there is no grounding for the headphones jack. The solution: some serviceman, long ago, got the plugs on the isostats board mixed up. These "molex" - like plugs are identical. Maybe it happened even in the original Dual factory.

When writing this post, the CS 704 finished to play the vinyl and the amp stayed at idle for some time. I heard twice a mechanical "glitch" inside the housing, not sure if amp, tuner, deck or turntable, but...

It reminds me of... A typical relays sound. Is it possible that the improper design issue with IC and a cap you mentioned could cause such a behavior? The amp is on for about an hour. No signal to the inputs when the issue occurred. Edit: it happened again and this time it was more like a thermal expansion sound.

You see, my joy was not for long but I decide to stay happy anyway

All The Best,

Mike

wacholder · 7. Februar 2023

Hi Mike !

Zitat von Pykon

I am located in Warsaw, Poland.

Another neck of the world I haven't made it so far.

Maybe when I retired ... *If* it is possible to travel then anyway.

Zitat von Pykon

Technically it is possible with small currents that are unable to burn the cap.

Tantaliums have a slightly strange behaviour.

They are *very* sensitive to ripple - more than any other electrolytic cap.

The first generation ("drop style") has liquid electrolytics - and *that* frequently destroys the insulator and the cap either looses capacity or - more likely - develops a short. On a small current it just shorts the line. Problematic when it is used as a separation capacitor between amplifier stages. If it is used as a buffer capacitor in e.g. regulation stages and the current is sufficient the tantaliums break the cases and spill the electrolytics everywhere. And if there is more current and voltage behind they even explode with a short explosion and a very intense hot flame. In the end only the connecting wires were stuck in the board - and the rest of it spread inside the gear ...

Back then in the early 1980s I worked for a company that made electronic processor boards for industrial washing machines. Board in the size of a toilet seat with hundreds of chips. And also hundreds of tantaliums as local voltage buffers for the supply voltage. We had a quality problem with these. Some of the boards did not pass the final quality control. After a brief decision-making chat with the co-workers I took off all the socketed 74LS-chips and the processor components. Then I attached a Volkswagen Käfer 6V battery to the +5V rails.

The capacitors in question were 10µF / 6.3V. After I applied the voltage it took about 15 seconds until the first cap blew off. Three more followed. I replaced them with some that withstand a direct "battery check" - stuffed back the chips and the board passed.

Zitat von Pykon

It reminds me of... A typical relays sound. Is it possible that the improper design issue with IC and a cap you mentioned could cause such a behavior? The amp is on for about an hour. No signal to the inputs when the issue occurred. Edit: it happened again and this time it was more like a thermal expansion sound.

I don't think that it *caused* the problem. But it is one nail in the coffin, I'd say.

Did you try to whack the case when the fault comes up ?

The relais *is* shut during that, but the contacts have improper and insufficiant contact. A slight hit to the sides could re-align them ... for a while. I really don't think it "fixed itself". It will need attention and maintenance. And probably a change of circuitry as described with the 4093 and 2.2µF for the timing-capacitor.

Zitat von Pykon

You see, my joy was not for long

I guessed it.

Zitat von Pykon

but I decide to stay happy anyway

No reason to get angry. A bit disappointed maybe, but not angry.

Anger is negative. They can't pay you enough to louse up the day with that.

Pykon · 8. Februar 2023

Hi Peter

After reading your above post I assume I will never use any tantalum cap in any home electronics I have. To close the topic positively (adding another negative could also generate the same effect, at least in theory ) I did some testing on the relays and they seem to be fit as new. Visually clean and even contacts, plus not any voltage parallel to the contacts when playing CV1400 at pretty high load. No current leak and immediate, blistering quick an clean on/off action. I am sure 100 percent that "relays" problem was a 4195 IC1113 tantalum issue. And I understand perfectly your doubts about it because I would never believe if someone told me that a cap on the inputs board could bring such a cracking "waiting for the signal" effect. But of course, I can be wrong.

By the way - as I do not want to bother you all here with a new so simple thread - I have CS704 and CS20 (1215). Both, as I remember well from the schematics, have contacts that should disconnect the stylus from the output cable when the tonearm is on the rest position. Please - tell me if I am wrong because on both units the stylus remains active even when the turntable is off and the tonearm on the rest.

PS. Until today, I used to replace the "Knallfrosch" in every Dual amp that joined my home Dual family. But from now I will also replace both tantalum caps on the inputs board. The access is not that bad, provided that the backplate of the amp's chassis was removed. For the purist's peace of mind, I can solder 10 uF electrolyte caps with some 100 nF in parallel. But as I found in the article you had linked before (that about replacing one 4195 with two simple voltage regulators) the noise after 4195 reached no more than 1000 Hz. With such a frequency, a regular, simple 10 uF electrolyte cap should cope very well. And there is no need of using some exclusive miracle low-impedance caps for filtering, even if the harmonics occupy the acoustic frequency range. I am not good in theory or practice, but that is what I can say I know

Best,

Mike

wacholder · 8. Februar 2023

Hi Mike !

Zitat von Pykon

By the way - as I do not want to bother you all here with a new so simple thread - I have CS704 and CS20 (1215). Both, as I remember well from the schematics, have contacts that should disconnect the stylus from the output cable when the tonearm is on the rest position. Please - tell me if I am wrong because on both units the stylus remains active even when the turntable is off and the tonearm on the rest.

Depends on.

On the 1215 the muting switch is only active when the cam wheel rotates. This is designed to suppress noises coming from the mechanics during automatic start and during transport of the arm after stop - either record end or using the function lever. It shorts signal and signal return on both channels. If it would open the circuit it would result in amplifier hum. After the cam wheel stops the contact is released and the pickup is active again.

At the 704 ... I don't know at which point the muting switch is activated anyway. It has no cam wheel and no automatic functions. At the end of the record it stops the motor and lifts the arm. Wonder if the muting switch is active there, but I really don't know. On mine I have never checked that.

Zitat von Pykon

After reading your above post I assume I will never use any tantalum cap in any home electronics I have.

*That* would be complicated.

They are used in computers and all "computerized" gear in masses.

However these are "solid tantalium" caps. These black or yellow "bricks" that are SMD-ed on every board to buffer the supply voltage on far away regions. But they don't tend to blow off the way their "liquid tantalium" anchestors do.

Pykon · 10. Februar 2023

Zitat von wacholder

At the 704 ... I don't know at which point the muting switch is activated anyway. It has no cam wheel and no automatic functions. At the end of the record it stops the motor and lifts the arm. Wonder if the muting switch is active there, but I really don't know. On mine I have never checked that.

Hi Peter,

I checked out the CS 704 service manual and the muting switch should work as followes:

"After playing a record, the contacts are closed. If the tonearm is returned to its rest, the contacts are reopened"

...so the behaviour of my CS seems to be accurate: in the rest position the stylus remains active. To give it a cleaning the amp volume has to be decreased to zero. So the 704 is OK. Beautiful machine, very soft an delicate to operate, precise and modern in form. The only puzzling flow of the design is the plastic chassis with almost no torsional rigidity. And the chemistry behind the 220V cables inside and outside of the unit. I remember that when replacing two "Knallfrosch" caps and soldering the insulation of these cables literally melted in hands. If you put this cable to the boiling water it would dissolve I thouhgt about replacing the grid cable but had no idea how to disarm plastic cable passage ring on the trafo housing. These passage rings are present at the back of any Dual electronics from these days. Looking simple but no idea how to let the cable free for replacement.

PS. After repair CV1400 working like a charm. The crakcs turned out to be the chassis thermal expansion. Strange but that was always the case: sound from turntable is significantly quieter than form e.g. tuner or deck. I am waiting for the Tonar stylus for CS and hope that will increase volume of 704. Moreover, I am planning to start a new thread regarding the CT1440 tuner because it sounds as it had a huge "mega bass" or "loudness" built in. It is indeed a mega-bassy guy so I will try to collect the votes from other users if they have same impressions.

PS. II Could you please tell if I am using the chat's functionality in a proper way when completing a selective quotation post: the only way I found was to use the "Quellcode" button and then... You know mess with the code of the previous post containing quotations.

Have a nice weekend,

Mike

wacholder · 10. Februar 2023

Hi Mike !

Zitat von Pykon

I checked out the CS 704 service manual and the muting switch should work as followes:

"After playing a record, the contacts are closed. If the tonearm is returned to its rest, the contacts are reopened"

That's what I guessed it would do.

Because you can hear "stylus cleaning" from the speakers if you don't turn down the volume.

Zitat von Pykon

I thouhgt about replacing the grid cable but had no idea how to disarm plastic cable passage ring on the trafo housing. These passage rings are present at the back of any Dual electronics from these days. Looking simple but no idea how to let the cable free for replacement.

Depends on.

Usually on the "newer" turntables the cables go through a bracket fixed with two screws.

The cables themselves are held with a plastik piece that *can* be squeezed with a pair of pliers at one side and therefore shrinks *a little bit* which is enough to push it back autoside from the metal plate.

That leaves the problem with the proper cable ends in the connecting box on the 704. They use special click-connectors that are not that easy to get off - neither are they available elsewhere as new parts. The major reason, "new" power cables are often cut inside the case, clamped, soldered, heat-shrinked or use these notorious "lamp clamps" for connection keeping the original connectors.

Zitat von Pykon

PS. II Could you please tell if I am using the chat's functionality in a proper way when completing a selective quotation post: the only way I found was to use the "Quellcode" button and then... You know mess with the code of the previous post containing quotations.

Looks okay to me.

When quoting you highlight the quoteable part with the cursor / left mouse button.

A drop down menu appears from which the right-hand "Zitat einfügen" puts the highlighted part into your new answer at the point where the cursor was located before you jumped back to quote something.

The left-hand option "Zitat Speichern" stores the quote for later use. On the side bottom you have a blue square with "X Zitate" - this is where they got shown. If you click on that they are listed and you could either remove ("Zitate entfernen") or insert selected ones ("Zitat einfügen"). Nothing clicked applies to all quotes, once you select one it is individually handled.

Pykon · 22. Februar 2023

Hi Peter!

My CV1400 is up and running, but as I started to repair another one for my Father, I realized that... Despite your good advice, in the previously fixed "main" CV1400 I overlooked two tantalum caps on the input selection board (the one with isostats). Firstly, I thought that "two of them" means two caps in the whole amp unit, that was my mistake. Secondly, there is a bug in the service manual: A and B currents are, in fact, mistaken with C and D. I simply could not find the second voltage regulator (on the boards) and its tiny blue tantalum filters - they stay hidden under several cables.

Hope that a horizontal position of these two remaining tantalum caps (on contrary to the ones on the inputs board) will give them some extra life but that awareness does not make me calm. From my modest experience, I observed that the IC1446 tantalum bombs fail less often than the IC1113 surrounding ones. And I hope this is truth. The CV1400 that I have currently on the table (and I mean real table in my dining room ) has both tantalum caps on the inputs board surrounding IC1113 replaced with some 5x bigger 35V, green ones. Or maybe this is a factory improvement from Dual itself? Blue bombs of IC1446 remain untouched.

I also made another mistake - and cannot judge if a serious one. I replaced "Knallfrosch" filtering caps in all my Dual units with generic 47 nF 1 kV MKP capacitors, the biggest I could buy. Today I read in one of the posts on the forum that the filtering cap is actually not a regular cap but must have at least X2 insulation class certificate. My 1 kV caps are not signed with X2 nor X3 or even an X like old yellow caps used to be. What remains to me is a hope that these new caps will not fail or blow - I put them also into the Revox B250 power supply filtering.

That is for report purposes and my "main" CV1400 history track

I have just started a new thread with the second CV1400 preamp section repair (hiss in the left channel).

All the best from the windy Poland,

Mike

wacholder · 22. Februar 2023

Hi Mike !

Zitat von Pykon

My CV1400 is up and running, but as I started to repair another one for my Father, I realized that... Despite your good advice, in the previously fixed "main" CV1400 I overlooked two tantalum caps on the input selection board (the one with isostats). Firstly, I thought that "two of them" means two caps in the whole amp unit, that was my mistake.

It has "two of them" for each RC4195.

The one on the input board - and the one on the input selector board.

Zitat von Pykon

Secondly, there is a bug in the service manual: A and B currents are, in fact, mistaken with C and D. I simply could not find the second voltage regulator (on the boards) and its tiny blue tantalum filters - they stay hidden under several cables.

There are various mistakes on several service manuals.

Sometimes the drawing people and their supervisors seemed to have a pretty bad day. Depending on local Schwarzwald celebration days ...

On the capacitors for the regulators in the schematics they got some numbers wrong on one as well.

At IC1113 the capacitors has to be C1153 (labelled C1126 as on IC1146) and C1152.

Zitat von Pykon

I also made another mistake - and cannot judge if a serious one. I replaced "Knallfrosch" filtering caps in all my Dual units with generic 47 nF 1 kV MKP capacitors, the biggest I could buy. Today I read in one of the posts on the forum that the filtering cap is actually not a regular cap but must have at least X2 insulation class certificate. My 1 kV caps are not signed with X2 nor X3 or even an X like old yellow caps used to be. What remains to me is a hope that these new caps will not fail or blow - I put them also into the Revox B250 power supply filtering.

That "X2" specification has been made for foil capacitors that are constantly attached to line voltage.

It assures that they don't start to burn in case of a failure. That's a european thing however and "other countries" - namely Japan - generously ignores it. Well ... in a country with 100 earthquakes a year and the lowest voltage end-customer supply network at 100V~ you have other things to consider. For the "export units" to high-voltage countries like Germany or the UK they used to use ceramic capacitors rated at 400V~ / 1000 or 1200V=. Often shrinked in plastic wrap. If *they* fail you're not gonna miss it: they fly apart in scrapnells like an old WW2 hand grenade. Barely - but do. Ceramics - you know. They *do* these things.

But generally they are as safe as using X2-rated foil caps. I have japanese HiFi gear from the early 70s and these caps still work and show no signs of wear or cracks.

Zitat von Pykon

That is for report purposes and my "main" CV1400 history track

Thanks for keeping us updated. Every experience presented may help "later generations".

Zitat von Pykon

I have just started a new thread with the second CV1400 preamp section repair (hiss in the left channel).

Seen that already but was a tad too busy to write something useful or at least share my thoughts on it.

Apparently the source *is* the pre-amp section and you could test with a signal generator if the hissing noise is frequency sensible when turning the treble and bass pots. To isolate the source you need to know if it starts in the sound control or earlier.

And probably test with a scope if the "hiss" is in fact an oscillation phenomenia.

The hiss part should come up on the scope with no signal as a ripple. Simply test all output pins on all OpAmps should help to locate the source.

I'd never experienced that sort of failure up to now.

Pykon · 22. Februar 2023

Zitat von wacholder

That "X2" specification has been made for foil capacitors that are constantly attached to line voltage.

Hi Peter!

The MKP 1 kV 47 nF capacitors I soldered into my Duals in fact are constantly attached to line voltage when the units are on. And the caps are foil ones with no "X" specification. To be precise, they are 47nF 1000V 5% 15mm EPCOS MKP. EPCOS means TDK Europe Do you think I should replace them with X2 caps?

I will measure the second CV1400 preamp circuitry and report what happened. One interesting fact: in the plastic-sided CV1400 the RC4558 op amps are replaced with lower noise RC4559 ones. I do not know if it altered the output noise level of the whole amp, but at least it is a sign of some in-factory progress.

Best,

Mike

wacholder · 22. Februar 2023

Hi Mike !

Zitat von Pykon

Do you think I should replace them with X2 caps?

No.

Unless you want to rework each and every unit you'd always used them on.

If you calculate 230V AC mains voltage you have to multiply it with 2 (for positive and negative swing) and multiply it with a square-root of 2 to get the peak-to-peak voltage. That gets you to around 650V and is the equivalent *minimum* voltage the capacitor has to withstand.

750V is already good, so is 800V and with a 1000V type you should have enough "head room" with these.

Dual CV1400 - IC 1113 short circuit

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