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Advice requested on repair Yamaha CA-1000

In class A, point/wire B is not connected/open circuit. VR603 is not in play. Agree, sorting out normal, seems it was kind of
working originally but now... Maybe a can of freeze spray to work out what's hot? If you are waiting then measure the resistance
from points +/-50 and +/-B all to GND/chassis, ie, 4 measurements. I've got a amp here I can run comparisons on.
 
jansen2810 said:
2. Normal does work, but unstable, protection kicks in one and a while, but it comes back. (8 Ohms dummy-
load, on bulb current limiter and variac, both channels same results, see first pictures) Sinus and squares look 'spiky' rough on the edges.
Click to expand...
Kinda working... Not !!
 
If you figure out whats going on in normal mode. Most likely will solve the class A issue.
 
Thinking out loud...
Regulated supply (both rails) are being dragged down even though
the current (F704) is not excessive. Maybe D701, D702 failing
under load? F701, 702? Current actually decreases when load
(1->2 power amps) increases... transformer??

Amp responds to bias adjustment, can set to 47mV and 940mV.

Bright DBT though F704 current is not abnormal. So(?) high
current from unregulatd supply driven by high TR606Vbe, ie, high
current through R617? or TR605 intermittent (c-e short?)

Will sleep on it.
 
Well, lots to be done then. I hope it's not the transformer, it crossed my mind though. It's unobtainable usually. At the moment doing things for money, called work. ;-)
 
avionic said:
Yes.... Just verified on a CA-800/1000 here.
For trouble shooting adjust the bias (idle current) for both Normal and Class A to zero volts. 0.0000001 vdc or as close to zero as possible for both amplifiers. Leave them at zero until you get (normal) mode working. I'm not even interested in class A right now.



sneak preview.......
CA-800 that I just finished up. Pretty much the same as the CA-1000.In fact the amplifier assemblies are from a CA-1000.View attachment 1670879
Click to expand...

Well we are getting somewhere. Bias to zero, in both modes relay clicks in, normal glowing DBT. Have not had the time yet to do some testing or taking measurements. I thought you like to know.
 
Measure +/-50, +/-B voltages to get a baseline. Then slowly adjust VR603 (normal) to 47mV if possible, stop at any point
where +/-50,B dip more than 2Vdc or the DBT glows continuously. Remeasure +/-50,B.
EDIT: Also measure Vdc at wires B to GND, repeat for wire C to GND.

Wind back the VR to zero and repeat on the other side. Same problem?

EDIT: Don't suppose you have an oscilloscope to look at the regulated supply?
Also replacement rectifiers
MUR.JPG
 
Last edited:
mbz said:
Measure +/-50, +/-B voltages to get a baseline. Then slowly adjust VR603 (normal) to 47mV if possible, stop at any point
where +/-50,B dip more than 2Vdc or the DBT glows continuously. Remeasure +/-50,B.
EDIT: Also measure Vdc at wires B to GND, repeat for wire C to GND.

Wind back the VR to zero and repeat on the other side. Same problem?

EDIT: Don't suppose you have an oscilloscope to look at the regulated supply?
Also replacement rectifiers
View attachment 1672124
Click to expand...

Oscilloscope? Look at the beginning of this thread :-) Am I looking for a ripple?
 
mbz said:
Thinking out loud...
Regulated supply (both rails) are being dragged down even though
the current (F704) is not excessive. Maybe D701, D702 failing
under load? F701, 702? Current actually decreases when load
(1->2 power amps) increases... transformer??

Amp responds to bias adjustment, can set to 47mV and 940mV.

Bright DBT though F704 current is not abnormal. So(?) high
current from unregulatd supply driven by high TR606Vbe, ie, high
current through R617? or TR605 intermittent (c-e short?)

Will sleep on it.
Click to expand...

TR604 in right amp is running extremely hot. One can smell the heat. Not so on the left. Bias zero (In class A before warning!)
In AB smoking hot!
 
Last edited:
What I am going to do. Take right main amp out, recap, replace TR606 and check TR604 en 605, new VR multi-turns, take drivers and endtransistors out en check. As posted before TR605 is getting steaming hot, only in right amp. (bias in normal 0,001). I will check +/-50vdc for ripple with scope. Replace the two diodes D701 and D702 if needed. I will check R619 again. OK?
 
mbz said:
The transistors should be tested, maybe TR605 failed short c-e, or "someone" is asking it to work hard.
Check/replace parts and check regulated supply wave, check ac and dc
Click to expand...
I will just do that. Something else, is on the schematic TP1/TP2 correctly drawn? They are between 50v en R610, but should T1 not be at the 1.3v site of TR601?
 
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