SX-626 having problems after complete recap and transistor change

[larryderouin]

S1 3/5 F =
S1, Input Selector
3/5, 3rd wafer of 5 (middle wafer) 1st wafer closest to Front panel, 5th wafer closest to Rear of Unit.
F = FRONT R = REAR

 

[fredlari]

S1 3/5 F =
S1, Input Selector
3/5, 3rd wafer of 5 (middle wafer) 1st wafer closest to Front panel, 5th wafer closest to Rear of Unit.
F = FRONT R = REAR

Thank you Larry!

 

[larryderouin]

The schematic's might seem a bit weird for the 626, but also remember that PIONEER was learning how to draw them out so people could read them. If you look at a SX-1500(from Previous series years) and a SX-636(Next series Years) you'll see a lot of improvements in layout, component ID, and voltages at certain spots. INDIVIDUAL BOARD DRAWINGS are from the SOLDER SIDE, NOT from the component side, so just be aware of the differences when locating parts on the board.

 

[fredlari]

update!

Since the problem on the right side was present on radio and phono, I figured maybe something was wrong with the head amp W21-004. Indeed there was, I changed both the ksc1845 on the right channel and it came alive! So the input selector is perfectly fine.

Now I tackling the power amp wich still blows a fuse on one side and all my transistors are good.

Is HFE testing with a DMM any good and reliable? I'm having doubts about the output transistors even if the HFE checks out.

thanks!

 

[EastPoint]

Just check the outputs for continuity, all 3 ways (pin to pin, each pin to case. If they're shorted or show anything under 800k ohms they're probably bad.

 

[fredlari]

It's finally over! The problem on the amp unit was that C11 was disconnected. As soon as i resoldered it wham. The fuses stopped blowing, I was able to adjust bias and reassemble the unit! Great sound! Thanks sooo much everyone!

 

[fredlari]

UPDATE

this is pathetic, it stopped working after a few hours. So now. I will strip bare the amp board, check every part out of circuit, replace if needed, clean the board with acetone and reassemble everything.

wish me luck, I'm getting tired of this

 

[fredlari]

Ok so I rebuild the power amp, It came back to life, no fuse blowing anywhere. I figured I would let it play radio for the night, to see if it would play in the morning (and not be silent with a blown fuse like before).

7 am, my teenage girl wakes me up and says! Theres a radio playing very loud in the garage! Big scatchy sound, very distorted! I think it's gonna blow! Do something!

So sure enough, the left side is crackly/staticky, very loud, not dependent of the volume and the woofer moves like crazy.

I turned it off and will look into it over the week-end. Will begin by checking of the preamp section is still behaving normally, then I will recheck all the transistors. Maybe a transistor that checked out gave in after all the soldering/resoldering. Worked a few hours then died.

I am not giving up! This SX-626 will work soon and for good, you can be sure of that!

 

[rcs16]

I hate when that happens.
Agree isolate the problem to either pre or power amp section. inspect your work, solder joints can be checked with ohmmeter(DMM), check continuity from one device lead to another device lead, that are connected together, copper trace or wire, (the same net) compare against the schematic, foils.
go over the BOM(parts list) and the placement, semi orientations.
Look for burnt components. Much of my troubleshooting is done with power off and use the DMM in ohms modes.
Then, if above does not detect anything, start checking all your DC bias points with the DMM ( reference to chassis ground), since one channel is working okay? then compare the DC bias points between the schematics and the other channel.
You could use load resistors for testing vs the speakers but you need to monitor the outputs to see what's going on, DMM(ACV) or scope, best to use a steady signal level with a sine wave source rather than music if using the DMM. There you go 40 years of electronics troubleshooting in a nut shell, wish you well.

 

[fredlari]

Hello everyone.

The problem was on the control amp unit, a transistor KSA992 was acting up. I changed it and now everything SEEMS to work fine BUT!

I cannot adjust the bias correctly on the left channel. Voltage is 57V on the casing of Q9 but stays at 21.7V on the casing of Q11 even if I turn VR1 from one side to another. I can change the voltage (15mV) across R31 on the white wire with VR3 though.

Right channel is acting normally. (57V on casing of Q10, 28.5V on casing of Q12 and 15mV across R32)

Also some static appears when the voltage on the casing of Q11 fluctuates (all by itself) then comes back to 21.7V.

Can anybody tell me what could cause this? a bad connection? D1 STV-3 is going bad?

thanks,