Interesting Dual CV1500 restoration challenge...for the German audience...

gslikker

Super Member
I decided to put progress here, for leisure. This is a very interesting amp. One of the first "computer-controlled" amps.

I presume they are that rare,probably only well-known in Germany.

The story started here....

My CV1500 has an input problem, probably a bad circuit card contact on the backplane, since the inputs are directly connected to the circuit card, making it prone to bad solder joints/pcb cracks...
In the end, it only works while pushing a bit on backplane connectors.

Now trying to open it up the proper way, I see almost burnt components, a lot of dirt (it is greasy inside, it was in a "less tidy" house when I bought it), and there is no easy way to loosen the back.

So what happened: I disassembed further, I ended up having a pile of cabling and pieces, the mid frame including transformer (which is also taken apart now).

This will be a time consuming and challenging piece.

I need to observe esd precautions due to the cmos chips, also. Also components made by companies I never heard of are in: NKL capacitors, SSS (Solid State Scientific) cmos chips. The UNOBTANIUM in here probably is the NS microcontroller, a COP420 preprogrammed device,

The first question for the opamp experts already arises: How is other peoples experience about the RC4559 opamp?
It is full of RC4559NB opamps, The only other restoration info I found is from the German dual-doktor.de site, they seem convinced they are prone to failure.

Now here are the leisure pics of the pile of funny circuit cards.

CV1500--1.jpg cv1500mess1.jpg cv1500mess2.jpg cv1500mess4.jpg
 
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I found some time to put the big parts under water with some dish wash detergent in it, took the box to work where we have compressed air and dried the metal stuff afterwards.
Despite the metal and circuit card mess, I just realized this amp has very little cabling. Just some small cable trees with (good) connectors. I put those in the water, too, as well as the caps and rectifier.
cv1500wash.jpg
 
Starting on the easiest part to familiarize: the power supply board.
It is a funny design having pre regulator resistors, transistors and voltage regulators, one of the regulator outputs even depending on a lower voltage one.

Observations:
1. pcb burn marks, blackened or discoloured components (a diode was at fault in my CT1540 tuner so these have to go).
2. It is a 220Volts unit, power nowadays can be over 230

Decision is lower the zener voltages, add cooling to two of the voltage regulators suffering most, and to the transistors as well.
Evaluate resistors. Now, for the two input resistors being 5 Watts now, the value is "best guess" as current is unknown at the moment. They might need adjustment.
It was decided leave in transistors and voltage regulators, because of the mounting type (the long tabs) and for the transistors base connection is in the middle.
The output capacitors are tantalums, which have 125 degrees celsius specification.
NOS parts were used for the changes.

dual-cv1500-pwrold2.jpg dual-cv1500-pwrold1.jpg dual-cv1500-pwr-part.jpg dual-cv1500-pwrnew1.jpg dual-cv1500-pwr-sch1.jpg
 
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Hello, I'm no electrician, but maybe this site in german helps: http://www.n-malek.de/11201/38347.html. Interesting are the naming of replacment types for old transistors.

To the RC4559: it should be replaced by LM833N. (Norbert Malek suggests this on his page...)

Thank you! I did know about his very nice site but I did not take the time to read it through this time.

Another note they fail and should be replaced.

This is what I was looking for: more evidence of failures !

I do have a lot of NOS parts, LM833 I do not know but I am sure having quite some NE5532, so I will do replacements.

I see mr Malek also did a thorough evaluation of everything suspect in the amplifier.
 
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some progress....a picture of the microcontroller.
Partly repopulated input board. Apparently IPA dissolves the PAINT on the solder side, making it ugly. I did not want to push chemical deterioration of boards any further so I just sprayed with SK10 and it looks okay again. There is NE5532 opamps on it, now.
Standby power board appears to have its circuit breaker holders consiting of one high and one low part, apparently they thought the fuses hold better that way. (which is debatable)
Some part exchanges and added a piece of metal for more cooling of the 7805

dual-cv1500-ctl-new.jpg dual-cv1500-bck-new.jpg dual-cv1500-sby-old.jpg dual-cv1500-sby-new.jpg
 
I put together the middle of the amp, apart from recap the trimming pots have been replaced by fixed resistors.
Driver transistors are not mounted yet. I will add the caps as per the recommendation on the site of Mr Malek and measure for differences when testing commences.
I still have to measure bias later to see if sufficient.

At first, I was not aware of the amp moving out just a few millimeters to be able to take it off the frame is sufficient, so I will find out later if the amp including heatsink can be taken out when the whole amplifier is assembled.

Now, it is a matter of finishing the wiring on the assembly and then the main amp unit can be tested as a separate unit.

The Caution to be taken working on the power amp is the fact the whole circuit card is mounted to the (8) pins of the output transistors, without any further mechanical support.

Also interesting is the transformer as it is mounted on rubber inserts, like a computer hard disk. During cleaning I took the weight of the transformer its bare weight is 3 kilo's without its enclosure frame.

dual-cv1500-mid-amp.jpg
 
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I love the look of this amp, my Dad had the CV 120 back in the mid '70s.
Good luck with the rest of your restoration.
I look forward to seeing the finished product!
 
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Suddenly, last winter the restoration bug was gone, but a few weeks ago I found this project in the way and I decided to start work on it once more.

Last winter, I did have the separate boards finished.

My aim always is to make as much pictures as possible, to see how I have to put things together again, this proved extremely valuable.

So, having forgot most I did I started to put things together. In the end, except for the outside parts, everything was together again, I just fired it up having enough voltage on the standy board to work, using a variac.

I seems working allright and the contact problems are gone!

Pictures for the picture addicts, comments may follow.
 
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Only thing remaining is take measurements, I even forgot to measure the mods I made to the power supply.........Sor far so good.

Connection problems and bad contacts solved, all electrolytics except the big ones replaced, supply modified as stated above and opamps replaced.

And also a few pictures of my tuner here (I have to update this page, but as it is not supported nor payed for as the service is obsolete, my internet provider might delete all one day.)
http://members.quicknet.nl/gerard.slikker/dualcv1500ct1540.htm

One thing noteworthy: I stayed in St-Georgen for work nearby several times, during the era this series of equipment was built.....not aware I would own anything from there later on.
 
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tonight I did put the old stuff together for listening, so far, so good (together with another collectors item, a Philips CD300).
Although, one thing I do not like is the volume potentiometer for the microphone input on the amp. It is larger than the other buttons.
It should be pushbutton too, or it would be better if it was not there, at all.

2017_1113_205817800x600.jpg
 
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I do not like is the volume potentiometer for the microphone input on the amp.
IMO better to have as is if planning on using mic. Not all mics are same impedance or sensitivity and I'd bet euro mics vary, too.

Nice collection.
 
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