SX-525 - loud pop when turning speakers on

[PapaGino]

I'm having an issue with my receiver - in any stage and at any volume, theres a large crackling POP over the speakers when they are switched on. Its less dramatic when I power the unit on, and let it set in 'speaker off' for a few minutes - but there is always a pop.

Switched out many of the transistors on this unit a couple years ago, with the help of Mark the Fixer. Various diagnostic measurements look ok last i checked - I've pasted a list of what was replaced to date. Any ideas where the issue could lie?


As of May 21, 2016 - Parts list and replacements - items marked in green were replaced:


Power Supply
AWR-007 C5 220uF 50v CEA: 647-UPW1H221MPD6
AWR-007 C6 47uF 16v CEA: 667-EEU-FM1E470 47uF 25v
AWR-007 C7 330uF 35v CEA: 667-EEU-FM1V331 330uF 35v
AWR-007 C8 470uF 25v CEA: 647-UPW1V471MPD 470uF 35v
AWR-007 C9 220uF 25v CEA: 647-UPW1E221MPD

AWR-007 Q1- 2SD313- E or D: 512-KSC2073TU

AWR-007 D1 - FR2-02: 512-1N4004
AWR-007 D2 - FR2-02: 512-1N4004
AWR-007 D3 - SIBO1-02: 512-1N4004
AWR-007 D4 - SIBO1-02: 512-1N4004
AWR-007 D5 - SIBO1-02: 512-1N4004
AWR-007 D6 - WZ-320: 512-1N5257B

Main Amp
AWH-006 C1 1uf 25v CSSA: 539-SN010M025ST
AWH-006 C2 1uf 25v CSSA: 539-SN010M025ST
AWH-006 C7 220uF 35v CEA: 647-UPW1V221MPD6TD 220uF 35 Volts
AWH-006 C8 220uF 35v CEA: 647-UPW1V221MPD6TD 220uF 35 Volts
AWH-006 C9 47uF 50v CEA: 647-UPW1H470MED
AWH-006 C10 47uF 50v CEA: 647-UPW1H470MED
AWH-006 C17 2.2uF 50v CEA: 647-UPW1H2R2MDD
AWH-006 C18 2.2uF 50v CEA: 647-UPW1H2R2MDD
AWH-006 C21 10uF 16v CEA: 647-UPW1E100MDD 10uF 25v
AWH-006 C22 220uF 50v CEA: 647-UPW1H221MPD
AWH-006 C23 100uF 50v CEA: 647-UPW1H101MPD
AWH-006 C24 47uF 50v CEA: 647-UPW1H470MED

AWH-006 Q1 - 2SA572- 4B, 5A, or 5B: 512-KSA992FBU
AWH-006 Q2 - 2SA572- 4B, 5A, or 5B: 512-KSA992FBU
AWH-006 Q3 - 2SA572- 4B, 5A, or 5B: 512-KSA992FBU
AWH-006 Q4 - 2SA572- 4B, 5A, or 5B: 512-KSA992FBU
AWH-006 Q5 - 2SC1318- R or Q: 512-KSC2383YTA
AWH-006 Q6 - 2SC1318- R or Q: 512-KSC2383YTA
AWH-006 Q7 - 2SC1318- R or Q: 512-KSC2383YTA
AWH-006 Q8 - 2SC1318- R or Q: 512-KSC2383YTA
AWH-006 Q9 - 2SA720- R or S: 512-KSA1013YBU
AWH-006 Q10 - 2SA720- R or S: 512-KSA1013YBU
AWH-006 Q11 - 2SC789-O: 512-KSD526Y
AWH-006 Q12 - 2SC789-O: 512-KSD526Y
AWH-006 Q13 - 2SA489-O: 512-KSB596Y
AWH-006 Q14 - 2SA489-O: 512-KSB596Y
AWH-006 Q15 - 2SC1318 R or S: 512-KSC2383YTA
AWH-006 Q16 - 2SC1318 R or S: 512-KSC2383YTA

AWH-006 D1 - 1S2O76:
AWH-006 D2 - 1S2O76:
AWH-006 D3 - SV-4A:
AWH-006 D4 - SV-4A:
AWH-006 D5 - 1S2076:
AWH-006 D6 - SIBO1-02: 512-1N4004 (?)

Head Amp
AWF-003 C1 3.3uF 16v CSSA: 647-UKL1H3R3KDDANA 3.3uF 50v
AWF-003 C2 3.3uF 16v CSSA: 647-UKL1H3R3KDDANA 3.3uF 50v
AWF-003 C7 .47uF 25v CSSA
AWF-003 C8 .47uF 25v CSSA
AWF-003 C9 3.3uF 25v CEA: 647-UPW1H3R3MDD 3.3uf 50v
AWF-003 C10 3.3uF 25v CEA: 647-UPW1H3R3MDD 3.3uf 50v
AWF-003 C15 100uF 35v CEA: 647-UPW1V101MPD
AWF-003 C16 100uF 35v CEA: 647-UPW1V101MPD

AWF-003 Q1 2sc871 E or F: KSC1845FTA
AWF-003 Q2 2sc871 E or F: KSC1845FTA
AWF-003 Q3 2sc870 E or F: KSC1845FTA
AWF-003 Q4 2sc870 E or F: KSC1845FTA

Control Amp
AWG-011 C1 .47uF 25v CSSA:
AWG-011 C2 .47uF 25v CSSA:
AWG-011 C5 100uF 6v CEA: 647-UPW1A101MDD 100uf 10v
AWG-011 C6 100uF 6v CEA: 647-UPW1A101MDD 100uf 10v
AWG-011 C7 1uf 25v CSSA: 539-SN010M025ST
AWG-011 C8 1uf 25v CSSA: 539-SN010M025ST
AWG-011 C19 47uF 50v CEA: 647-UPW1H470MED
AWG-011 C20 47uF 50v CEA: 647-UPW1H470MED

AWG-011 Q1- 2SC1000- GR or BL: 512-KSC1815YTA
AWG-011 Q2- 2SC1000- GR or BL: 512-KSC1815YTA

 

[ConradH]

Have the two big output caps been changed? (C6/7 ?) The symptom is leaky output caps. Put a DVM on the outputs, no speakers, and see if there's a large voltage on turn-on that takes near forever to come down. Normally there should be some bleeder resistors that hasten the matter, but not if the DC leakage is very high. Or, I could be completely wrong- troubleshooting at a distance is a dart game.

 

[larryderouin]

Conrad's on the mark. The Main Filter Cap (C5 on Schematic) and the OUTPUT CAPS (C6 & C7 on Schematic), should have been replaced. If they are original, replace.

 

[PapaGino]

Will do, thanks all!

 

[larryderouin]

Do NOTE that the replacements will be approx 25% to 40% smaller than the original can caps. You can either remove the CAN CAP and replace it with the new one in the clamp using some self stick window weatherstripping, OR (this is a neater option) gut the can and fit the new cap inside.

 

[ConradH]

Don't know the size, but sometimes you can find snap caps of the same diameter, but way shorter than the originals, that fit the clamps.

 

[PapaGino]

Theres no clamps, the old caps were glued to the board, looks like this pic:

In that case, am I clear to replace directly?

 

[larryderouin]

Yep. The UPW's should drop right in. No Glue needed, but DO scrape off the old glue.