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Yamaha CA-1000/CA1000II Power Supply and Protection Circuit Diagnostics, & Lower SNR values with the QA403

mbz said:
Point to the above, rather than just posting voltages, diy your own analysis and post what you think is happening, sure we get it wrong some times but that's how we learn rather than being spoon fed...
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I have been begging for explanations as you have just posted for three years now, I can learn from such explanations! All this other BS that others have provided goes into that DOG FOOD pile you explained last night! :bigok:
 
I can tell you at this moment that TR601 - TR612 are not shorted or open and the hfe #'s are as specified.
 
mbz said:
Plz, 1 step at a time so I can follow your thinking, may get to TR601,2 later.
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Yep, TR604 and 605 are "reverse biased" Ve > Vb so the transistor is off, need Vb > Ve for current floe/on condition.

Next step in the thought process should be "ok, which voltage is wrong/ at fault."
Since both transistors are off there is no e-c current flow so no current/volt drop through R619 so would expect Ve to be about -50 rail
so...
 
I am seeing Vbe on TR604 & TR605 to be greater than 0.6v, I think?
I am seeing a voltage drop across R619, I think?
 
Yamaha5000 said:
I am seeing Vbe on TR604 & TR605 to be greater than 0.6v, I think?
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TR604 and 605 are "reverse biased" Ve > Vb so the transistor is off, need Vb > Ve for current flow/on condition.

Yamaha5000 said:
I am seeing a voltage drop across R619, I think?
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So, under the circumstances, what does that tell you?

Happy to admit I may have the analysis wrong, certainly TR604,5 base voltages look like a key symptom however for the moment would like to understand R619 volt drop, approx 8Vdc / 68ohms approx 110mA, R619 is a 85mA fusible. You probably have a metal film, in any case I'd measure R619, has it drifted high?

edit the other possibility being either TR604,5 is breaking down e-c allowing a leakage current through R619
 
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Nashou66 said:
That is not a cement resistor. It's a fusible resistor. These types have fuses in them and no longer are used . If you used too much heat to remove it you may have caused it to go open .
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That is very good information, Thank You
With the voltage measurements that I was getting, I would think it was blown prior to removal. I don't know when it blew since it was fine yesterday. Maybe Gremlins! :eek:
 
FYI: I replaced the R619 and now everything is working as it should to conduct the AMP Board Calibration. Now I will button it back up and see if it continues to hold. Will keep you posted. :beerchug:
 
FR704 became very hot and has a black burn mark around it's center but still measures 3.9ohms. PL and protection has stopped working. Tested some of the components in the PS and haven't found anything defective so far. Will pick it up again tomorrow.
 
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