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Advice requested on repair Yamaha CA-1000

Post #1, test 4. Suggests regulated power supply issue.

Possible multiple issues with amp going into protect in class A.

The 2SC458's on the CA-1000 are the outhouse/rectangular shaped.
Some people get confused by the pinout, looking at the bevel face it's
e/c/b, looking at the printed face it's b/c/e. The probable replacement
KSC1845 is e/c/b. The icons on the power supply board are correct (only
error I recall is TR304 on tone board).

On Normal, B+ of 46.5V is a bit low, probably due to a slight increase
in current draw/"shorting"

TR709B=0V so relay is off. Problem could be excessive dc so amp goes
into protect or maybe a power supply issue, Zener D704? TP3 and TP4
voltage measurements will check for excessive dc. Consider removing the
2 fuses in one power amp side and see if you can identify faulty channel.
 
mbz said:
Post #1, test 4. Suggests regulated power supply issue.

Possible multiple issues with amp going into protect in class A.

The 2SC458's on the CA-1000 are the outhouse/rectangular shaped.
Some people get confused by the pinout, looking at the bevel face it's
e/c/b, looking at the printed face it's b/c/e. The probable replacement
KSC1845 is e/c/b. The icons on the power supply board are correct (only
error I recall is TR304 on tone board).

On Normal, B+ of 46.5V is a bit low, probably due to a slight increase
in current draw/"shorting"

TR709B=0V so relay is off. Problem could be excessive dc so amp goes
into protect or maybe a power supply issue, Zener D704? TP3 and TP4
voltage measurements will check for excessive dc. Consider removing the
2 fuses in one power amp side and see if you can identify faulty channel.
Click to expand...

First off all, thanks for all the explaining! These are my thoughts: regulated powersupply should deliver +50v/-50v both in A en AB (right?). In A in drops down to + and -26v. I suspect a short in one of the main boards, so both main boards get only 26v, as all the other boards (functionboard etc...), which could explain the cutoff of the negativ cycle of a 1kHz signal I put in once. My intention was indeed to disconnect one power amp from the regulated PS to see if I get my 50v back. My conclusion would be, that the regulated PS must be ok then. Next thing would be the restoration of the faulty power amp or try to find out what component is only activ in class A. Btw I am familiar with the different pinout of those 458's and the like. I did measure the bias/off set settings, but forgot. I do them again. They were not far off. (1 p.amp, I do them both now)
 
There are 4 power feeds into each power amp. They are marked,
+/-50 which is from the regulated supply. It's 50Vdc in both
normal and class A

+/-B from the unregulated supply. Provides about 50Vdc in normal
and about 20Vdc in class A.

Please confirm that it's the +/-50 or +/-B pins that drop to 26V
Like the man says
avionic said:
The regulated +/- 50vdc should not drop.
Click to expand...
 
mbz said:
There are 4 power feeds into each power amp. They are marked,
+/-50 which is from the regulated supply. It's 50Vdc in both
normal and class A

+/-B from the unregulated supply. Provides about 50Vdc in normal
and about 20Vdc in class A.

Please confirm that it's the +/-50 or +/-B pins that drop to 26V
Like the man says
Click to expand...

The regulated PS drops to 26v, that's not ok, I understand, but.... I get it back when I remove the fuses of BOTH power amps. Relais clicks in. That's making it even more complicated. Just for now I am out of ideas. So now same values in both class A AND normal. B+ 48,7/B- 49,8 with bulb-limiter (short flash in class A, longer in normal.)
 
jansen2810 said:
The regulated PS drops to 26v, that's not ok, I understand, but.... I get it back when I remove the fuses of BOTH power amps. Relais clicks in. That's making it even more complicated. Just for now I am out of ideas. So now same values in both class A AND normal. B+ 48,7/B- 49,8 with bulb-limiter (short flash in class A, longer in normal.)
Click to expand...
I'm not getting a warm fuzzy feeling here. The fuses are for the unregulated power supply. The unregulated supply comes right off of the two large filter capacitors.
 
avionic said:
I'm not getting a warm fuzzy feeling here. The fuses are for the unregulated power supply. The unregulated supply comes right off of the two large filter capacitors.
Click to expand...
My first intention was to disconnect the two/four +/-50 connections for that matter and leave the fuses alone. But you guys are the experts, so I followed instructions ;-)
 
Carefully measure dc voltage at one side of F704 (47ohm, as pix), black probe connected to chassis or any black
speaker post. Then measure the other side of F704 to GND. Expect about 65Vdc one side and 60Vdc the other
 
The regulated
jansen2810 said:
Right on the regulated powers supply board, where it says +B/-B. Black lead on E, red lead on +/-B
Click to expand...
Ok..Can also measure it on the brown and violet wires that go to each amplifier assembly.
 
jansen2810 said:
You changed TR705,706,707 and 709 for fresh ones?
Click to expand...
The pic is not one of my amps. Generally I will replace TR705, TR707, TR709 being 2SC458's, I wouldn't use Nichicon ES
(bright green) with Nichicon EP being a better choice. I'd use Nichicom PW for the other caps,
upload_2019-11-11_12-31-10.png

With amp powered off/unplugged, operations switch set to class A, black
meter probe inserted into any black speaker post, measure the resistance
at wire "B" on left power amp. Repeat for wires A, C, S, these 3 should
give the same result. Need to verify no near short, anything less than 500
ohms would be a concern. Repeat for right power amp.

Please try to get all requested measurements, without them we/I loose interest very fast.
 
mbz said:
Generally I will replace TR705, TR707, TR709 being 2SC458's,
Click to expand...
Why? They are in the protect DC detection circuit.No signal path there..2SC458LG's get noisy -- that really wouldn't matter in this app.
 
avionic said:
Why? They are in the protect DC detection circuit.No signal path there..2SC458LG's get noisy
Click to expand...
Yeah, fair call. Thought was noise is noise, in the extreme case don't want it to lead to relay chatter. Also while the amp
is open and at a cost of a few cents. Not a strong arguement I agree. A bit like coupler switches, do they all need to be dismantled
and cleaned on this CA series? In the past I would have left them if they ohmed out ok, but not so sure now, seen too many
dirty ones...
 
mbz said:
The pic is not one of my amps. Generally I will replace TR705, TR707, TR709 being 2SC458's, I wouldn't use Nichicon ES
(bright green) with Nichicon EP being a better choice. I'd use Nichicom PW for the other caps,
View attachment 1669433

With amp powered off/unplugged, operations switch set to class A, black
meter probe inserted into any black speaker post, measure the resistance
at wire "B" on left power amp. Repeat for wires A, C, S, these 3 should
give the same result. Need to verify no near short, anything less than 500
ohms would be a concern. Repeat for right power amp.

Please try to get all requested measurements, without them we/I loose interest very fast.
Click to expand...

Well I understand and as far as I know always did. I will post the measurements because I really like this amp to work. I already replaced the BP caps with Nichicon ES, because I had them in stock.
 
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