Pioneer SX-727 Crackle and pop

[grindfix]

First, let me thank everyone who helped me rebuild my SX-1280. Special thank you Markthefixer for providing BOM and detailed guidance. I got about 4 months of 1-2 hrs/day on it and it performs and sounds awesome. At first, I wasn't impressed, but I knew that all new capacitors need time to break-in. Sound eventually opened-up and I think it still gets better and better every day!

New project (one of many) is SX-727 with it's common crackle. Cleaned pots, switches and trim pots on Amp board. Set Bias to 20ma/DC to 0mv. Left channel was initially dropping out sounding like cough then eventually cleared. I suspect weak capacitor somewhere. Now it's been playing for several hours and occasionally, there is a crackle. My plan is to rebuild Power Supply and replace all small transistors and e-caps on the Amp board AWH-011.
I found some old threads with info. Does anyone have current parts list for this receiver?
Thanks

 

[markthefixer]

I haven't done a reverse engineer for the replacement transistors.
The caps are almost up to date (just checked) , 2 values for a total of 7 caps have gone obsolete or problematic.
one is 0.47uf film cap
other is 1uf 50v or greater.
No time to figure out replacements right now, others probably have. They'll chime in (I hope).

 

[larryderouin]

PRELIMINARY!!! DO NOT USE UNTIL VETTED BY MARK!


Mark; Take your pick. Probably others but I used your guidelines for this.

0.47uf 50V
Nichicon... http://www.mouser.com/ProductDetail...=sGAEpiMZZMv1cc3ydrPrF652zNprbYwMkWvn1Y212qE=
WIMA........ http://www.mouser.com/ProductDetail...=sGAEpiMZZMv1cc3ydrPrF7l45uRd9dVhExePEl6XCE8=

1uf 50V Film
Nichicon.... http://www.mouser.com/ProductDetail/Nichicon/UMA1H010MCD2TP/?qs=QB0ovJDgFgtHTr1B4NGuNA==

1uf 50v Lytics
Nichicon
UHE Series... http://www.mouser.com/ProductDetail...=sGAEpiMZZMtZ1n0r9vR22e0BBN1kF1oiuvGryroGz0U=
UKL Series... http://www.mouser.com/ProductDetail...GAEpiMZZMtZ1n0r9vR22RPm77sS3Lwx%2bcPhT4OlSXQ=

GRINDFIX: DO NOT USE THIS UNTIL VETTED BY MARK.

 

[larryderouin]

grindfix; This is INFO ONLY. Don't order any until Mark Vetts the list. Personally of the two brands, I would go with the Nichicon's in the film types due to longer leads. Most of the WIMA's have very short leads and very often need lead extensions.

As for the Lytic's, The UHE series would go in the Power Supply Section while the UKL go in the signal path.

If Mark says go with the Films for everything, then that makes it a lot easier.

Larry

 

[grindfix]

Mark
Have you had a chance to look into this?
Thanks

 

[larryderouin]

GRINDFIX; Mark is super busy this time of year, so go with the Nichicon's. I use them in my PIONEER gear (sx-737,939,790 and 434) so they are proven in at least 4 receivers.

Larry

 

[zebulon1]

Replace the transistors that appear in this post. All others should be fine.
The Head amp and AF unit probably will be where the noisy transistors lay.
The AF Unit uses the JEFT's (Q1,Q2) stay clear of them. No current replacements, should be OK.
It's a shotgun approach to troubleshooting but with a high fix'n probability.

Top 10 worst 70's transistors.
Vintage HiFi Transistor Replacement Table

Type Replacement(s) Failure notes
--------------- ----------------------------------------------- ------------------------------
2SA720 KSA1013
2SA725 KSA992 or BC327 Shot noise
2SA726 KSA992F or KSA992E or BC327 Shot noise
2SA798 (2x) BC560B or (2x) KSA992
2SA809 KSA1381 Poor heat dissipation
2SC458 2SC2240 or KSC1845F or KSC1845E Leakage, noise, static
2SC631 KSC1845 (but test for hfe 350+) Prone to failure or noise
2SC632 KSC1845 (but test for hfe 350+) Prone to failure or noise
2SC871 KSC1845F or BC550C Leakage, noise, static
2SC1000 KSC1815Y Leakage, noise, static
2SC1312 2SC2240 or KSC1845 or BC337
2SC1313 2SC2240 or KSC1845 or BC337
2SC1318 KSC2383Y or KSC2690AY Thermal stress, thermal flex
2SC1344 2SC2240 or KSC1845 Static burst
2SC1451 KSC3503 Static burst, open circuit faults

 

[jj1977]

I just had my transistors replaced and fully cleaned my SX-727 played for about and hour and the static pops and crackle noises returned again as before it was repaired now it comes and goes what is causing this thanks

 

[larryderouin]

jj, most likely capacitors, if they weren't replaced. Start with the POWER SUPPLY. Then do the main amp(s) board(s), and work back until the EQ board.

 

[zebulon1]

What transistors?
Are the pops and crackle in both channels?

 

[jj1977]

What transistors?
Are the pops and crackle in both channels?

It appears to be on the right side also pressing the fm mute high/low filters seems to disturb it even more making the static Even worse frustration

 

[jj1977]

It appears to be on the right side also pressing the fm mute high/low filters seems to disturb it even more making the static Even worse frustration

I have had the SX1500td for a month 3rd trip back and this SX-727 less than two weeks and back to the tech again

 

[jj1977]

I have had the SX1500td for a month 3rd trip back and this SX-727 less than two weeks and back to the tech again

Hopefully it’s the Capacitors the transistors have been replaced on the SX727 well we’ll see wish I new how to work on these