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SX626 no sound

qprhooligan

qprhooligan

Well-Known Member
I have a SX626 and here is what I know about it so far. The main fuse is good. The unit powers up and lights work but there is no click a few seconds after turning it on. The 2A right and left fuses are blown. I was told by the person i got it from that they replaced the 2A fuses but they just blow again. So I am not sure what the first thing I should do to try and get this working again. I have a DMM and downloaded a manual and will do what I can.

Any help?

Thanks.
 
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Easiest to just replace the transistors... although you could look for the bad ones, but marginal ones can slip through.

mouser.com parts numbers:

Q13 2sc938 150v 0.05a 0.6w
512-KSC2383YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17

Q1, Q2 2sc732 50v 0.15a 0.4w 200-700hfe 150mhz
512-KSC1845EBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

Q7, Q8 2sa497 100v 0.8a 0.6w 40-240hfe 50mhz
512-KSA1013YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17


Q3, Q4, Q5, Q6 2sc497 100v 0.8a 0.6w 40-240hfe 50mhz
512-KSC2383YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17

Q9, Q10, Q11, Q12 2sc793 100v 7a 60w 20-300hfe 9mhz
863-MJ21194G npn to-3 250v 16/30A 250W 8-75hfe 4mhz $4.23


before replacing them but after you have them, talk to us about how to get the transistors connected correctly, the replacement's layout can be DIFFERENT than the originals.

caps:
awh-002 c1 3.3 10 cea 3.3 50 647-UPW1H3R3MDD $0.14
awh-002 c2 3.3 10 cea 3.3 50 647-UPW1H3R3MDD $0.14
awh-002 c3 100 50 cea 100 50 647-UPW1H101MPD $0.28
awh-002 c4 100 50 cea 100 50 647-UPW1H101MPD $0.28
awh-002 c5 3.3 50 cea 3.3 50 647-UPW1H3R3MDD $0.14
awh-002 c6 3.3 50 cea 3.3 50 647-UPW1H3R3MDD $0.14
awh-002 c7 100 50 cea 100 50 647-UPW1H101MPD $0.28
awh-002 c8 100 50 cea 100 50 647-UPW1H101MPD $0.28
awh-002 c11 100 6 cea 100 10 647-UPW1A101MDD6 $0.15
awh-002 c12 100 6 cea 100 10 647-UPW1A101MDD6 $0.15
awh-002 c13 2200 35 ach-004 2200 35 647-UPW1V222MHD #1.34
awh-002 c14 2200 35 ach-004 2200 35 647-UPW1V222MHD #1.34
awh-002 c21 100 50 cea 100 50 647-UPW1H101MPD $0.28
 
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Ok, so basically rebuild the AWH-002 board. I ordered the parts today and I will let you know when they arrive.

Thanks again for the help Mark.
 
Fedex just dropped off the parts. I guess I'll be replacing the transistors and caps. Should I remove the board from the receiver to work on it? I know I have to unscrew the mount brackets to move it around to get access but I could leave the wires connected and still do the solder work I think.

I will wait for instructions.
 
Leave the wires connected to the board. They are wire wrapped around pins. Mechanically and electrically a stronger joint than solder. Be very careful moving the board, and lift the wires out of the retainers to give all the slack you can give to the wires. This will make it easier to move the board around. The wire is solid and breaks very easily if mishandled.

I'm doing a QX-747A right now and the wiring is a Gold Plated ___________!!!

Larry
 
Q13 2sc938 150v 0.05a 0.6w
512-KSC2383YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17
Click to expand...

My manual lists this as 2sc983 and I guess its just a typo.
Original(ECB) - KSC2383(ECB)
Q1, Q2 2sc732 50v 0.15a 0.4w 200-700hfe 150mhz
512-KSC1845EBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea
Click to expand...

Original(ECB) - KSC1845(ECB)
Q7, Q8 2sa497 100v 0.8a 0.6w 40-240hfe 50mhz
512-KSA1013YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17
Click to expand...

Original(EBC) - KSA1013(ECB)
Q3, Q4, Q5, Q6 2sc497 100v 0.8a 0.6w 40-240hfe 50mhz
512-KSC2383YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17
Click to expand...

Original(EBC) - KSC2383(ECB)
Q9, Q10, Q11, Q12 2sc793 100v 7a 60w 20-300hfe 9mhz
863-MJ21194G npn to-3 250v 16/30A 250W 8-75hfe 4mhz $4.23
Click to expand...

Original(PIN 1. BASE, 2. EMITTER, CASE: COLLECTOR) - MJ21194G(PIN 1. BASE, 2. EMITTER, CASE: COLLECTOR)

before replacing them but after you have them, talk to us about how to get the transistors connected correctly, the replacement's layout can be DIFFERENT than the originals.

caps:
awh-002 c1 3.3 10 cea 3.3 50 647-UPW1H3R3MDD $0.14
awh-002 c2 3.3 10 cea 3.3 50 647-UPW1H3R3MDD $0.14
awh-002 c3 100 50 cea 100 50 647-UPW1H101MPD $0.28
awh-002 c4 100 50 cea 100 50 647-UPW1H101MPD $0.28
awh-002 c5 3.3 50 cea 3.3 50 647-UPW1H3R3MDD $0.14
awh-002 c6 3.3 50 cea 3.3 50 647-UPW1H3R3MDD $0.14
awh-002 c7 100 50 cea 100 50 647-UPW1H101MPD $0.28
awh-002 c8 100 50 cea 100 50 647-UPW1H101MPD $0.28
awh-002 c11 100 6 cea 100 10 647-UPW1A101MDD6 $0.15
awh-002 c12 100 6 cea 100 10 647-UPW1A101MDD6 $0.15
awh-002 c13 2200 35 ach-004 2200 35 647-UPW1V222MHD #1.34
awh-002 c14 2200 35 ach-004 2200 35 647-UPW1V222MHD #1.34
awh-002 c21 100 50 cea 100 50 647-UPW1H101MPD $0.28
Click to expand...

I also have all the caps. Should I go ahead with replacing all the caps and transistors noting the new pin layouts I got from the manual and from the data sheets for the new parts? Or is there some other bugaboo you needed to warn me about?

Thanks.
 
Looks good, pay close attention to the electrolytic capacitor's polarity as you remove them, replacing each with the new one - ONE AT A TIME!!

Sometimes the polarity can be mismarked on the board.
 
Replaced all the caps and transistors listed. I did test the big transistors for shits and giggles and Q9 and Q10 were OK while Q11 and Q12 were bad. I didn't test anything else.

I broke one of the wire wrapped wires while soldering and I reattached it it seems OK.

Have built a dim bulb tester. (what watt bulb should I use?)

It is all back together now and I'm ready for the next step.

Thanks.
 
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did you replace the bad Q11 & Q12? Make sure they were greased ok and NOT shorted to ground or anything? If so we can proceed.

re: DBT ... 60 watt's ok, maybe 100's... if the 60 starts to glow a lot when bringing up the idle current - but for this power level of receiver, it shouldn't be an issue.

The bulb causes a brownout condition, the higher the wattage the less the brownout. Sometimes the brownout causes the protection to stay out because it doesn't "look turned on", depending upon the model and the circuitry.

Bring it up on the dim bulb, with the two VRx's on the amps at zero ohms.

Listen for audio.

Then we TEST set the idle current on the DBT, leaving it at zero when going off the DBT (it would be too high when plugged straight into the wall). and then off the DBT set it for real.

the setting / reading is 15 millivolts across an 0.5 ohm emitter resistor for that channel. need more detail?
 
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qprhooligan said:
I see 4 VRx's and I'm not sure which 2 to set to 0 ohms.

And not sure where the 0.5 ohm emitter resistor is.
Click to expand...


sigh..... not gonna get much bench time in today.... :tears:

vr1 and vr2 set an internal voltage in the amp for halfway between 0v and the 58 v (or so) power, vr3 and vr4 set the idle current in the output transistor stages, which flows from + 58v through Q10, R32 (0.5 ohms), q12 & R34 (0.5 ohms) to ground or zero volts.

Set VR3 and VR4 to zero ohms for zero or minimum idle current since work was done to either the power supply or the amplifier.

measure the voltage on the metal case of Q10 (to ground), then use VR2 to set the voltage on the metal case of Q12 (to ground) to half of Q10's measured voltage.

measure the voltage ACROSS (one dmm lead on each side of the resistor) R32 and use VR4 to set it to 15 millivolts.

transpose the numbers for the other channel.Q9, R31 (0.5 ohms), q11 & R33 and VR1, Vr3.
 
Well I may have messed something up. I turned on the unit with the dim bulb tester and the bulb glows bright all the time. I guess that means there is a short somewhere? I went back over it and double checked that I put in all the parts correctly and it seems I did. I'm not sure what to check now.
 
qprhooligan said:
Well I may have messed something up. I turned on the unit with the dim bulb tester and the bulb glows bright all the time. I guess that means there is a short somewhere? I went back over it and double checked that I put in all the parts correctly and it seems I did. I'm not sure what to check now.
Click to expand...


When you installed the power transistors, you were careful to align the bump in the socket with the recess in the heat sink, so that the holes, leads and screws were centered and not shorting to the heat sink?

Also you used the mica insulator with white thermal paste on all 4 output transistors?
 
markthefixer said:
When you installed the power transistors, you were careful to align the bump in the socket with the recess in the heat sink, so that the holes, leads and screws were centered and not shorting to the heat sink?

Also you used the mica insulator with white thermal paste on all 4 output transistors?
Click to expand...

I used the paste and mica insulators but I didn't align them with any bumps. I will remove them, test them to see if I fried them and reinstall them checking for bumps this time.

Would it hurt anything if I powered it on with the power transistors removed to see if the bulb dims?
 
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The Transistor mounts are the bakelite units the wires attach to. They have raised "bumps" on the ends where the encased nuts are. They fit into the holes on the heatsinks, centering the mount and the transistor, so no shorts occur hopefully.

If they are offset, you can short out the outputs in a flash........
Make sure the mount is FLAT against the heatsink, press the transistor to it thru the heatsink, then tighten the screws.

Larry
 
Would it hurt anything if I powered it on with the power transistors removed to see if the bulb dims?
Click to expand...

In this case, the sx-626 has a feedback path with the output transistors removed, so, you CAN power it up with the output transistors removed, and NOT hurt anything.
 
OK I think I have it figured out now. I need to order new mica insulators because I damaged mine when I kept remove the transistors.
 
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From the picture, there is no socket - instead the pins are soldered to the board???? Is this correct?

........534-4662 to-3 mica insulators $0.16 each.................
mouser.com

I keep on forgetting to include that number, as well as a number for a small quantity of thermal paste.
 
markthefixer said:
From the picture, there is no socket - instead the pins are soldered to the board???? Is this correct?

........534-4662 to-3 mica insulators $0.16 each.................
mouser.com

I keep on forgetting to include that number, as well as a number for a small quantity of thermal paste.
Click to expand...

That is correct, there is no socket and the pins are soldered to the board. The reason I couldn't see the little nylon shoulder that the transistors fit over at the end holes is because the heat sink was too far away from the circuit board and I have to push it closer to see them.

As for the insulators I already ordered the 534-4636 to-3 mica insulators. I hope those will work.
 
The socket has the "bumps".

In this case care has to be taken so the leads are only making the intended contacts, and not shorting out to something else.
 
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