SX-626 having problems after complete recap and transistor change

fredlari

New Member
Hello to you!

I hope I am not bothering you in any way but I need your help:

I purchased an SX-626 (1971 MODEL) for 40$, it did not work but was incredibly clean. I figured I would recap it and also change transistors and power resistors.

I did all the work and still have a few problems:

1. The power supply (awr-006) gives me only 15vdc on the 30v output (pin 5) (the KSC945 I did solder incorrectly as EBC but was actually ECB). It did output 30vdc for a few minutes after I correctly connect the KSC945 but now only 15v. The diodes are all new as well. I get 57V, 12V and 24V on other outputs (pins 3, 7 and 10)

2. I have no sound in the left channel when I listen on the preamp output, and crackling in the right, no music but crackling. Except on input AUX , I can hear sound (very faint) on that input, the balance, volume, bass/treble all work, but only on the right. Both channel work when I press mono/stereo.

3. The 57V 2A fuse on (awh-002) left chanel blows when I power up the unit (with speakers connected), I did replace everything on the power amp board except the 1/4w resistors. The variable resistors were replaced by bourns units and set to very low resistance.

The tuner seems to work, fm stereo lights up when on a channel and the meters move accordingly.

I know it's probably something minor so if any of you could give me a hint, you would make me very happy.

I have only a DMM to work with so I am limited.

thanks in advance.
 
1. the ksc945 (awr-006, awr-012, awr-029?? q2) was probably damaged, and took a few minutes to die when correctly installed - it COULD have taken the series pass element power transistor Q1 along with it. I would replace them both because current that went through and damaged Q2 HAD to flow through Q1 to get to Q2.. OR Q1 was damaged and took out Q2 when Q2 was put in correctly.

I haven't specified replacement transistors for the 626, and I tend to avoid the ksc945 BECAUSE it has TWO pinouts, ebc and eCb if the KSC-945 is followed immediately by a "C"...

Since I haven't specified them, PLEASE list the substitutions you used. ALL of them. It will take me some time to answer.


your hint: - you made the mistake of incorrect transistor installation once - recheck ALL with FRESH eyes - attack it from the attitude of "proving it's in there correctly". It stings less when one can quietly find ones mistakes. Use the DATASHEETS!!! And the layout diagrams - check which other components are connected to that transistor's lead's pc board trace for proof.

edit - VR1 is 30k center point voltage adjust. 0 ohms on that one may not be good. VR2 50 ohms idle current adjust can start from 0 ohms, but turn up vr1 to 15k - halfway. Then adjust the center point voltage to 1/2 the +b voltage.

edit2 - I gotta break off for a day or three.... just a head's up. Already stolen too much time and I'm trying to beat the oncoming cold snap.
 
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Thanks Mark!

I will verify all of this tonight and change the KSC945 with a KSC2383YTA.

Also, I saw smoke a few days ago when I tried to power up the unit, it came from the heatsink of the main amp unit. I checked the resistors but they are all good. could it be the varistor, the STV-3? Would a toasted varistor cause the fuse to blow? What would be the replacement for this?

I will post the complete list I used soon. Thanks for your help!
 
Seems like a classic case of doing too much work all at once. Perhaps the best approach would have been to isolate the problem preventing it from working in the first place and then, once running, go about the recap.

It will be tricky working with only a DMM. Have you made yourself a dim bulb tester at least, rather than plugging straight into the mains?

I find my autoranging DMM, signal generator / tracer and cheap old oscilloscope are invaluable tools.

Best of luck with the repair :)
 
Good day!

Yes I did too much work at once, must learn from this!

Here are the parts I ordered and where I placed them:


equalizer amp
W21-004 C1 10 16 CEA 10 25 647-UPW1E100MDD6
W21-004 C2 10 16 CEA 10 25 647-UPW1E100MDD6
W21-004 C7 0.47 25 CSSA 0.47 50 647-QYX1H474KTP
W21-004 C8 0.47 25 CSSA 0.47 50 647-QYX1H474KTP
W21-004 C9 3.3 25 CEA 3.3 50 647-UKL1H3R3MDD1TA
W21-004 C10 3.3 25 CEA 3.3 50 647-UKL1H3R3MDD1TA
W21-004 C15 100 35 CEA 100 50 647-UPW1H101MPD
W21-004 C16 100 35 CEA 100 50 647-UPW1H101MPD
Q1: 2SC871: 512-KSC1845FTA
Q2: 2SC871: 512-KSC1845FTA
Q3: 2SC870: 512-KSC1845FTA
Q4: 2SC870: 512-KSC1845FTA

control amp
AWG-008 C3 47 50 CEA 47 50 UPW1H470MED1TD
AWG-008 C4 47 50 CEA 47 50 UPW1H470MED1TD
AWG-008 C7 47 6 CEA 47 50 UPW1H470MED1TD
AWG-008 C8 47 6 CEA 47 50 UPW1H470MED1TD
AWG-008 C11 4.7 25 CEA 4.7 50 647-UPW1H4R7MDD
AWG-008 C12 4.7 25 CEA 4.7 50 647-UPW1H4R7MDD
AWG-008 C19 10 25 CEA 10 25 647-UPW1E100MDD6
AWG-008 C20 10 25 CEA 10 25 647-UPW1E100MDD6
AWG-008 C23 100 6 CEA 100 50 647-UPW1H101MPD
AWG-008 C24 100 6 CEA 100 50 647-UPW1H101MPD
AWG-008 C25 47 50 CEA 47 50 UPW1H470MED1TD
AWG-008 C26 47 50 CEA 47 50 UPW1H470MED1TD
AWG-008 C27 2.2 25 CSSA 2.2 50 647-UKL1H2R2MDDANA
AWG-008 C28 2.2 25 CSSA 2.2 50 647-UKL1H2R2MDDANA
Q3: 2SA572: 512-KSA992FBU
Q4: 2SA572: 512-KSA992FBU
Q5: 2SC1000: 512-KSC1845FTA
Q6: 2SC1000: 512-KSC1845FTA

power amp
AWH-002 C1 3.3 10 CEA 3.3 50 647-UKL1H3R3MDD1TA
AWH-002 C2 3.3 10 CEA 3.3 50 647-UKL1H3R3MDD1TA
AWH-002 C3 100 50 CEA 100 50 647-UPW1H101MPD
AWH-002 C4 100 50 CEA 100 50 647-UPW1H101MPD
AWH-002 C5 3.3 25 CEA 3.3 50 647-UKL1H3R3MDD1TA
AWH-002 C6 3.3 25 CEA 3.3 50 647-UKL1H3R3MDD1TA
AWH-002 C7 100 50 CEA 100 50 647-UPW1H101MPD
AWH-002 C8 100 50 CEA 100 50 647-UPW1H101MPD
AWH-002 C11 100 6 CEA 100 50 647-UPW1H101MPD
AWH-002 C12 100 6 CEA 100 50 647-UPW1H101MPD
AWH-002 C13 2200 25 ACH-004 2200 35 UPW1V222MHD
AWH-002 C14 2200 25 ACH-004 2200 35 UPW1V222MHD
AWH-002 C21 100 50 CEA 100 50 647-UPW1H101MPD
Q1, Q2 2sc732: 512-KSC1845FTA
Q3, Q4, Q5, Q6 2sc497: 512-KSC2383OTA
Q7, Q8 2sa497: 512-KSA1013YTA
Q9, Q10, Q11, Q12 2sc793: 863-MJ21194G, with new mica insulators and thermal paste applied.
Q13 2sc938: 512-KSC2383OTA


power supply
AWR-006 C5 100 35 CEA 100 50 647-UPW1H101MPD
AWR-006 C9 330 25 CEA 330 50 647-UPW1H331MPD1TD
AWR-006 C10 330 25 CEA 330 50 647-UPW1H331MPD1TD
AWR-006 C12 100 16 CEA 100 50 647-UPW1H101MPD
Q1, Q3 2SD313: KSC2073TU
Q2 2SC945: KSC945CGTA

tuner
AWE-011 C23 4.7 25 CEA 4.7 50 647-UPW1H4R7MDD
AWE-011 C27 1 50 CEA 1 50 647-USV1H010MFD
AWE-011 C29 4.7 25 CEA 4.7 50 647-UPW1H4R7MDD
AWE-011 C30 1 50 CEA 1 50 647-USV1H010MFD
AWE-011 C33 100 16 CEA 100 50 UKZ1H101MHM1TO
AWE-011 C36 10 16 CEA 10 25 647-UPW1E100MDD6
AWE-011 C38 0.47 50 CEA 0.47 50 647-QYX1H474KTP
AWE-011 C45 10 16 CEA 10 25 647-UPW1E100MDD6
AWE-011 C53 0.47 25 CSSA 0.47 50 647-QYX1H474KTP
AWE-011 C54 4.7 25 CEA 4.7 50 647-UPW1H4R7MDD
AWE-011 C55 3.3 16 CSSA 100 50 647-UKL1H3R3MDD1TA
AWE-011 C57 3.3 16 CSSA 100 50 647-UKL1H3R3MDD1TA
AWE-011 C58 1 50 CEA 1 50 647-USV1H010MFD
AWE-011 C61 0.47 50 CEA 0.47 50 647-QYX1H474KTP
AWE-011 C65 100 16 CEA 100 50 UKZ1H101MHM1TO
AWE-011 C66 2.2 16 CSSA 2.2 50 647-UKL1H2R2MDDANA
AWE-011 C67 2.2 16 CSSA 2.2 50 647-UKL1H2R2MDDANA
AWE-011 C73 47 16 CEA 47 50 UPW1H470MED1TD


main power cap 3300 63v 6800 63 647-LLS1J682MELC

if anything is wrong and you have the time and kindness of heart to look, please let me know!

again, thank you!
 
That's a very comprehensive list. You've probably replaced 75 - 80% of parts that really had nothing wrong with them.
 
Without being the technician or otherwise the person doing the work, it might be difficult to diagnose over the internet so to speak. My advice would be to pull the fuses for both the power supply channels, and get the preamp section working first. Start with getting the correct voltages at the power supply board, then check that there are no transistors installed wrongly. I'm not sure where the power amp bias and center presets should be for a starting position, it may be that one of them is turned all the way up. Certainly pull the outputs and check these, you can do this with your meter.

I would disagree with replacing parts that had nothing wrong with them. These old Pioneer receivers (and amps, etc.) often have transistors where the legs corrode, the corrosion travels up inside the transistor, and then it becomes noisy or just plain goes bad and takes out a lot of other stuff with it. 992s and 1845s are cheap enough to keep in stock to replace as and when.

Lee.
 
That's a very comprehensive list. You've probably replaced 75 - 80% of parts that really had nothing wrong with them.

That series of Pioneer is old enough that I'd do the same thing. All the sky-blue caps are bad, most of the transistors are iffy, bad, or heading that way, and the other electrolytics are heading downhill. Parts are cheap, and if you have the time, why not do it right?
 
That series of Pioneer is old enough that I'd do the same thing. All the sky-blue caps are bad, most of the transistors are iffy, bad, or heading that way, and the other electrolytics are heading downhill. Parts are cheap, and if you have the time, why not do it right?

Yeah I do agree with you but I'm looking at it more from a position of fix the fault before doing a full restoration. Some times its hard to see the wood for the trees :)
 
No one has said it explicitly: #1 fix the pin 5 30v regulator, new q1 and q2 (if you have it use a ksc2383).
The 13v zener is ok because pin 7 has ~ 13v on it. Do BOTH q1 and q2 at the same time. One old can hurt the other new transistor.

DBT only marginally useful on this model, and you are past it's usefulness here.

Dumb question: You have deoxited all the switches and knobs(pots)?
If not, deoxit!!

THEN reevaluate. EVERYTHING.
 
No one has said it explicitly: #1 fix the pin 5 30v regulator, new q1 and q2 (if you have it use a ksc2383).
The 13v zener is ok because pin 7 has ~ 13v on it. Do BOTH q1 and q2 at the same time. One old can hurt the other new transistor.

DBT only marginally useful on this model, and you are past it's usefulness here.

Dumb question: You have deoxited all the switches and knobs(pots)?
If not, deoxit!!

THEN reevaluate. EVERYTHING.

Deoxit was the fist thing I did.

Yesterday, I plugged in the unit and the power supply gave me 29V on pin 5. Let it alone for while then returned to see 13-15V fluctuating! Checked everything on the power supply (left a leg on the diodes and checked them also), I changed the KSC945 but the ksc2073 I did not have a brand new one, the HFE checks out. Still the same,

57 OK
30 NOT OK fluctuates from 13-15V
12V OK
24V OK

Could it be a faulty capacitor? That power supply is not complex at all, this is a mistery to me.

EDIT: I did change the ceramic 0.01uF capacitors with these R75RI21004030J DC Film Capacitor, 10000 pF, 1.25 kV, PP (Polypropylene), ± 5%, R75 Series
 
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UPDATE!

I have checked the preamp output on the unit and the FM/PHONOS/AUX all work. The sound is distorted because the supply to the preamp board is fluctuating from 13 to 17V. As the voltage increases, the stero separation increases and distortion disappears. So now I need my 30V.

I will go and buy some new transistors tonight for the power supply and remove all components from it, clean all the solder and also clean with acetone and then check all the traces to see if all checks out, test all parts en then reinstall the parts.

Wish me luck!

Then I will tackle the power amps, testing Everything!!!

Thank you all for your help, I will post my development.
 
Nice find! It sounds like you now know where the problem is. Good luck!
 
SUCCESS!

I removed everything for the Power supply board, removed the solder and cleaned it with acetone, then I tested all the parts et reassembled the power supply again. Bam! all 4 voltages are spot on! (must have been a short or a cold solder joint).

The sound in the right channel is still iffy on radio and phono, but not on tape and aux. So i will investigate the input selector switch, I shot deoxit 3 times in that thing but I think it is problematic. I will try to bypass the switch with cocodile plugs and post my findings.

As soon as the premap section is perfect, I will do the power amp section.

HAVE A NICE WEEK-END!
 
if you have d100 apply and let it set a few days before you flush and lube. the 626 i did,i did all the switches and the tuner shaft wipers in the begining and let it set all through the rebuild. its easier to see on the brass shaft wiper's but they were solid black in the beginning but after a week came to clean brass with a shot of contact cleaner
 
Thanks john stumpf, I will do that.

Now I have more questions. The balance pot on the unit (part number acv-104-0) is damaged but still working. What would be a replacement for this? I know it's a dual 500K but anything else I should know?

And I'd like to know the function of the Head amp unit, I know it serves as a phono preamp but I think the AM an FM are connected to it also. So does it modify these signals as well?

If I want to bypass the input selector and verify Radio, I jump pin 1 and 11 of w21-004 to 5 and 4 of the R-unit awx-007 (and phono inputs to 1 and 11 of w21-004 for phono?). And then pins 3/4/5 7/8/9 (two a a time) on w21-004 to 1 and 2 of aws-014? sorry this can be confusing.

Since aux and tape input are perfect, I figure everything after the input switch unit is working?!? Or am I mistaking?

Honestly, those round selector symbols with numbers confuse the hell out of me, S1 3/5F, for example, what does it mean?

thanks again, I hope I am not getting on the nerves of anybody.

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