Yamaha CA-810 repair

avionic said:
Just replacing a fusible resistor will not clear the short. The resistor is just a fuse. There is a possibility of a shorted transistor, diode or capacitor causing the fusible to burn open.
Click to expand...
I thought that might be a possibility still. Both of the driver transistors tested fine, and I am getting good sound through headphones with the left output transistors pulled. I ordered all new caps, so I will test as I go and replace all of those. I want to get it working before just shotgunning a bunch of caps in there.

If I am getting good output through headphones, doesn't that mean that the left channel main amp is doing its job? It only shorts with the output transistors in, so are there any components that would only show a short with the outputs installed and not short without them?

I guess if the fusible resistor and new caps don't fix that channel, then I will have to pull all of the components and test them until I find the bad part.
 
bberkom said:
I thought that might be a possibility still. Both of the driver transistors tested fine, and I am getting good sound through headphones with the left output transistors pulled. I ordered all new caps, so I will test as I go and replace all of those. I want to get it working before just shotgunning a bunch of caps in there.

If I am getting good output through headphones, doesn't that mean that the left channel main amp is doing its job? It only shorts with the output transistors in, so are there any components that would only show a short with the outputs installed and not short without them?

I guess if the fusible resistor and new caps don't fix that channel, then I will have to pull all of the components and test them until I find the bad part.
Click to expand...
Hopefully it was the output that burnt the fusible.
 
Well, I replaced FR409, the bad fusible in the left amp. I also replaced a couple of caps that I had to pull to confirm values for my order including the purple C603, but they weren't the problem. I fired it up on the DBT, and it passed with a relay click too, but I haven't installed the left output transistors yet.

I was going to test it with headphones before installing the output transistors, so I plugged it into full mains voltage. I turned it on and was about to turn up the volume, but the new 68 ohm FR409 immediately started smoking profusely! It was a new 1/2 watt metal film resistor. Something around that resistor is still shorting out even though it passed the DBT with no left channel outputs installed.

I tested the drivers TR421 and TR423 previously, and they checked out fine. And it worked fine with headphones with the old bad 68ohm FR409. The new 68ohm resistor got smoked just like the last one. I pulled and measured D417 out of circuit, and it tests fine.

Any advice on what else I should be looking at in the left channel amp?

Edit: I am using a 100w rated bulb in my DBT. Do I need to up the wattage of the bulb?
 
avionic said:
No.. You need to find the actual problem.
Click to expand...
Yeah, I guess that's the idea. I'm just not very good at that part of it yet when it's not obvious. I guess I'm going to pull the drivers again, test them, then keep going backwards with the rest of the transistors, diodes, and caps on that side.
 
Check C427 for possible short. Measure resistance of FR401 and FR403.(390Ω) .Check diodes D405,407,409 and 411.
 
C427 was not shorted, but I replaced it anyways with a new cap. FR401 measures 248 ohms. FR403 measures 328 ohms. Both a little low, but nothing crazy. I have 1/2 watt replacements for those as well.

FR405 measured 688 ohms, FR407 measured 690 ohms, and I went ahead and replaced them too since I have replacements.

I retested TR421 and TR423 while I was at it, and they're still fine. Diodes also test good, with approx DMM readings below.
D405 - 635
D407 - 638
D409 - 604
D411 - 608
D413 - 608

I am out of time today, but there is some brown glue around TR409 that looks pretty nasty, so I am going to pull it and test a couple of resistors around it that have glue on them. I'll pull the rest of the caps and test for shorts and replace them as well.
 
Those were actually measured out of circuit. I also thought it was strange that they were low since these usually climb higher.
 
I have 1/2 watt flameproof for them and already replaced them. They need to be 1/4 watt?
 
About C603 according to Holye. Its a 220µf @10volt (Z). When I see the (Z) suffix I use a low impedance capacitor ie. Nichicon PW.
 
avionic said:
About C603 according to Holye. Its a 220µf @10volt (Z). When I see the (Z) suffix I use a low impedance capacitor ie. Nichicon PW.
Click to expand...
I put a Nichicon UKL in there for C603. I could get a PW when I order more 1/4 watt fusibles and any other parts I end up needing if it will make a difference.
 
Z is the electronic symbol for impedance... Will it make a difference? UKL is a low leakage. Its probably better than the OEM one you removed.
 
Ill leave it for now but may order a PW eventually once it’s at least working again.
 
You must log in or register to reply here.

Similar threads

lucky5115
CR-1020 Transistor Replace
Replies
4
Views
666
brutal
brutal
lucky5115
Yam CR-1020 recommendation
Replies
9
Views
1K
lucky5115
lucky5115
gcgst
Yamaha CA-810 - protection relay question
Replies
2
Views
2K
gcgst
gcgst
gort69
2SB554/2SD424 and 2SB555/2SD425
Replies
4
Views
824
gort69
gort69
Willy6
ca-810
6 7 8
Replies
157
Views
6K
EvilDingo
EvilDingo
Back
Top Bottom