View Full Version : Pioneer SX-636 no output from left channel


nadude98
08-05-2009, 07:36 PM
I have my son's SX-636, it was working fine and then the left channel just quit. I have now given it a thorough DeOxit and cleaning...

Still no output from the left channel, it's dead.

nadude98
08-05-2009, 07:46 PM
I checked the Amplifier Adjustment on the left channel and I have -1.3v with an 8ohm dummy load and no input

nadude98
08-05-2009, 07:53 PM
Oh, it would probably be a good idea for me to at least recap the power supply and amp boards at least wouldn't it.

nadude98
08-05-2009, 09:09 PM
I did a search and found the transistor replacement on another thread. I replaced transistors Q 1,3,5,7 and 9. Left channel is now working again, however on the amp adjustment I cannot get down to 20mV on the left channel. The best I could achieve is 23mV. ????

Any thoughts?:D:scratch2:

markthefixer
08-06-2009, 12:20 AM
I did a search and found the transistor replacement on another thread. I replaced transistors Q 1,3,5,7 and 9. Left channel is now working again, however on the amp adjustment I cannot get down to 20mV on the left channel. The best I could achieve is 23mV. ????

Any thoughts?:D:scratch2:

another thread? what parts were used as replacements?

Come ON, I'm working blind here....

adjustment? bias I hope?

nadude98
08-06-2009, 02:14 AM
Here is the list from the other thread:

q1 & Q3 2sa763
512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

Q5 2sc1451
512-KSC2310YBU to-92 ecb 150v .05a .8w 100mhz 40-240hfe $0.11 ea

Those above are the most likely suspects, Q5 primarily. The rest are included for completeness....

2sa777,2sc1509 80v 0.5a 0.75w 50-220hfe 120mhz
512-KSA1220AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.39
512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40


2sb531,2sd371 100v 6a 20w 40-240hfe 5mhz
863-MJ21193G pnp to-3 250v 16A 250W 4mhz 8-75hfe $3.83
863-MJ21194G npn to-3 250v 16A 250W 4mhz 8-75hfe $3.83

mouser.com parts numbers....

markthefixer
08-06-2009, 03:34 AM
Ok, you are still running the original outputs?

WE need to read the base to base voltages at the output transistors at minimum bias on the pot on both channels, and at the correct bias point on the good channel. Red dmm probe on one base, the black probe on the other base of the output transistors for each channel.

Should be around 1 volt. The variations around 1 volt as you adjust the bias pot are critical.

I am assuming that you ARE talking about bias current.

I'm also surprised you didn't swap out the power output transistors.

nadude98
08-06-2009, 11:45 AM
I did not have output transisitors on hand, but I did have the rest. I will check those later today.

Thanks,

nadude98
08-06-2009, 02:22 PM
Ok, you are still running the original outputs?

WE need to read the base to base voltages at the output transistors at minimum bias on the pot on both channels, and at the correct bias point on the good channel. Red dmm probe on one base, the black probe on the other base of the output transistors for each channel.

Should be around 1 volt. The variations around 1 volt as you adjust the bias pot are critical.
1.11v right channel and 1.18v left channel and 1.16v with bias adjusted correctly on the right channel

I am assuming that you ARE talking about bias current.

I'm also surprised you didn't swap out the power output transistors.

If and when I do a cap order I will order outputs. It's just after ordering so many times I order quite a few extra of the transistors that seemed to be used a lot...:D

nadude98
08-08-2009, 12:16 AM
No Mas?

What could be causing the idle current to be so high I can't get it down to spec?

markthefixer
08-08-2009, 01:25 AM
No Mas?

What could be causing the idle current to be so high I can't get it down to spec?

The voltages are in the correct range, so there could be a fault with the power transistors. Too much leakage perhaps, maybe partially fried junctions.

Transistors of this type are cheap enough to just replace...

nadude98
08-08-2009, 02:55 AM
The voltages are in the correct range, so there could be a fault with the power transistors. Too much leakage perhaps, maybe partially fried junctions.

Transistors of this type are cheap enough to just replace...

Okay, is the list I have correct? Is there a recap list for the 636?

A little off the subject, I saw a Manual today that had schematics and circuit board layouts for all the Pioneer models of receiver, amps and shortwave receivers from the early 70's. How handy would something like that be? As far as receivers I noticed it had everything from the SX-424 to the SX-1010 plus the quads, just everything..... It was cool and looked almost brand new!