CA-1000 - Calling Yamaha techs - Help!

Macdude

Hi /on/ Fidelity
A few weeks back I found this CA-1000 in the trash down the street. I found it had a toasted resistor on the right channel and someone had replaced a 5a fuse with a 14a, leading to further damage. Upon further investigation, I found the outputs and drivers on the right amp board were shorted. Fusistors tested close to spec except for one on the power board that was open. Replaced them all to be safe. Found a burned up ground/earth trace on the function board and fixed it (this was throwing off my rail voltage very badly). Now I'm down to the last problem.

On the right amp board, I have good +/- rail voltage on both ends, however, I get no measurement between TP 3 and 4 (idle current adjustment cannot be performed). I also only get 11.6vdc between TP 1 and 2 (15v adjustment). I can't go any higher than 11.6vdc.

The amp comes out of protect every time. I replaced the Class A/B microswitches early on. Voltages are off the same amount in A/B mode. As of this post, I have replaced every transistor and electrolytic on that amp board except for the K34 with no noticeable change. All resistors on this board test in spec out of circuit. I'm running in circles.

All measurements are in vdc in Normal mode

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All measurements vdc in Normal mode

TR607:
E: .036
C: 1.2
B: .036

TR608:
E: -.036
C: -.07
B: -.47

TR609:
E: .70
C: .70
B: 1.3

TR610:
E: .10
C: .50
B: .05

TR611:
E: -.04
C: 50.5
B: .13

TR612:
E: -.04
C: -50.5
B: -.01
 
Hello !

I have replaced every transistor and electrolytic on that amp board except for the K34 with no noticeable change

Why did you replace them if you don't know if they are good or bad ?

How can you replace these transistors with new type ? Do you have original in stock (30 years old unit ! )

If you used sub can you tel us what sub you used ? and at what place ?

Waiting to read your answer ....
 
I'm no tech, but I see a cracked resistor right next to the fuses. That checked out ok as well?
And have you checked that the trimpots are okay?
 
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The resistor with the mark checked out fine. I'll have to pull the trim pots and check them out. I've never seen one go bad, just seen them get dirty.
 
Hello !

I have replaced every transistor and electrolytic on that amp board except for the K34 with no noticeable change

Why did you replace them if you don't know if they are good or bad ?

How can you replace these transistors with new type ? Do you have original in stock (30 years old unit ! )

If you used sub can you tel us what sub you used ? and at what place ?

Waiting to read your answer ....

The outputs and drivers tested bad when I removed them. The unit drew too much current with the originals in. I bought substitutes that I researched on this forum. I bought everything I would need worst case scenario to avoid future shipping costs. I'll be putting the good originals back in. Here is a list of what I used:

TR607/608: KSC1845FTA
TR604/605: 2SC3902S
TR611/612: MJ15016G/MJ15015G
TR609/610: MJE15034G/MJE15033G

All from Mouser. I didn't want to replace everything if I didn't have to, but I got tired of having no progress so I tried shooting in the dark and replacing everything to see if I'd make any progress. I didn't, so the originals will go back in once I figure this out.
 
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I'm certainly no expert tech either..it's a hobby. However, normally I do pretty well. This unit just has me a little lost. I had a hard time finding subs for the drivers and they may not be 100% correct. The amp wouldn't work at all with the originals, so the replacements could be the source of the problem.
 
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On the right amp board, I have good +/- rail voltage on both ends, however, I get no measurement between TP 3 and 4 (idle current adjustment cannot be performed). I also only get 11.6vdc between TP 1 and 2 (15v adjustment). I can't go any higher than 11.6vdc.
Have you pulled and tested the emitter resistors R633 and 634 ? (.47 ohm/5watt)
 
Ohm out the Class A/Normal slide switch at test points A,B,S & C on the driver boards. The slide switch is located between the two micro-switches.
 
Have you pulled and tested the emitter resistors R633 and 634 ? (.47 ohm/5watt)

They were out of spec so I replaced them early on. Forgot to mention that.

I'll check out the slide switch. That switch is almost completely hidden in there.
 
TR609:
E: .70
C: .70
B: 1.3

TR610:
E: .10
C: .50
B: .05

You should have rail voltage on the collectors of these two driver transistors.
Like + / - 51 vdc. Same as the output collector voltages.(TR611 & 612 )
Check for proper installation , solder connections , solder pad integrity, broken traces on the PCB. .:scratch2:
 
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I figured it out, and you're exactly right, avionic. When I installed the new drivers, I put a lead through a mounting hole for the old TO-66 style drivers. Turns out the hole I used (because it was closest) doesn't tie into the trace with rail voltage like the other hole. I bridged the gap and I was then able to bias the unit correctly. Still didn't have that 15 volts I needed between TP1 and 2. I removed and tested the trim pot.. fine. Everything else in the vicinity checked out, so I decided to swap the 2SK34 from the left amp board. Low and behold, the left side had been replaced before with a 2SK30A. The problem followed the newer part. Right amp is now at 15v, left side is down to 11.6. Looks like I need a 2SK34 or 2SK30. Probably completely NLA.

I've got it biased, offset down to 1mV. Sounds pretty damn nice!

Thanks for the help. I hope I don't need more. :D
 
Hello !

I see on your picture a 2,7K resistor who look "strange" closer to the 5,6K resistor .

Did you check it ?
 
Hello !

I see on your picture a 2,7K resistor who look "strange" closer to the 5,6K resistor .

Did you check it ?

Yes. I checked every resistor on the board with one leg removed. The charred one and the emitter resistors were the only ones out of spec. I replaced the fusistors as well for piece of mind. I have two NOS 2SK30A FETs in the mail.
 
Just as an update, the amp is up and running with two NOS 2SK30's installed. I put the good 1124's back in and dialed in all the adjustments. This is a wonderful sounding unit.
 
Just as an update, the amp is up and running with two NOS 2SK30's installed. I put the good 1124's back in and dialed in all the adjustments. This is a wonderful sounding unit.

Oh very good news. I was just about to enquire about the dry-looking solder joint for the black "E" wire on the bottom left of that pic, but you got it working!
 
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