Repairing then restoring my SX 737

snpcracklpop

New Member
Hi everybody! My 737 is cutting in and out with super loud popping and crackles (hence my name) if it sits for a long period it wil come on and work for about 5 minutes and then pretty much not work at all with occasional resurfacing for 10 secs. After reading through some posts I tried the tape monitor switches and they do have an effect while the receiver is making noise (its usual state is powered up with no sound).
I just ordered my deoxit and it clearly needs it, but I was wondering if there was any way to test the switches, or bypass them to troubleshoot? And do these switches interact with the protection board, which was what I thought was the issue and may still be?
I do plan to follow markthefixer's guide and restore for sound quality, but i would like to know the issue before the parts swapping begins.
 

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Lots of baddies in the 737. 2SA725 / 2SA726, 2SC1312 / 2SC1313 in the phono, preamp, and amp. If I recall this has 2SC1451 for bias in the amplifier as well. All of these need to be replaced and it may quiet the unit right down. While your at it replace the capacitors too.

737 is an excellent receiver well worth the time to fix it up.
 
Lots of baddies in the 737. 2SA725 / 2SA726, 2SC1312 / 2SC1313 in the phono, preamp, and amp. If I recall this has 2SC1451 for bias in the amplifier as well. All of these need to be replaced and it may quiet the unit right down. While your at it replace the capacitors too.

Replace which caps? Thanks for your input!

737 is an excellent receiver well worth the time to fix it up.
 
I just finished cleaning, recapping and replacing the troublesome transistors in my SX-737. It's a unit I bought at my work's salvage sale for $20 because it had a dead channel. (I work at UC Irvine, and sometimes the Professors offices have nice old vintage gear they get rid of when it stops working. Normally stuff like that gets scrapped but the guys save them for me, I pay by the pound for the salvage! :beatnik:

So, back to answering your question about replacing all the caps:
I have an old Tegam 252 Inductance tester that can measure capacitance and ESR on caps up to 200uF. Many of the 220uf caps measured out around 185 uF, as did one of the 330uf caps! The 100uF caps were mostly down to around 85uF. The worst caps were in the power supply. but surprisingly, the tuner had some bad ESR caps, too. ESR on some of the low value orange Sanyo caps was 90 Ohms! Most of the other caps read between 2-7 ohms ESR. Only a few of the caps measured at spec with good ESR.

So yes, replace them all! The unit sounds MUCH better! Almost no noise on the mic,aux phono and tuner where it had major static, before.
 
Thanks for the data! I've seen a lot of discussions about changing the caps for sound quality and some saying it made little, or no difference to them and it's not worth the effort, but those numbers don't lie! And greetings from Ohio State!
 
Replace the 2sc1451's on the Amplifier board 1st, along with the 2sa725/726's on the amplifier board. I've been using the "Rice Krispie's" term for this behavior in the sx-x3x series since I got my sx-1010 back in 2010. And it's an appropriate term. Both my 939 and 737 had the Rice Krispie's. IT was caused by the 1451's in the 939 and the 726/725's in the 737. You'll need to eventually do all of the boards, (caps and transistors) but only the transistors listed in the Mark The Fixer List. 99% of all PIONEER lists originated from him years ago and have been constantly updated. All the caps will need to be redone. The POWER SUPPLY needs to be done BEFORE ANYTHING ELSE. If the voltages aren't up to snuff, nothing else will be. Search thru the forum for 737 threads (and there are tons of them lately for a list of parts by MARK THE FIXER.) Copy and paste to this thread for vetting to get the latest parts & availability from Mouser. This will include all caps for all boards, plus all needed and required transistors. Once vetted, then you can order it. One stop shopping save a bunch on shipping.

There are powder Blue Sanyo Caps that are solid aluminum electrolytic's that turn to resistors eventually. ECHOWAR'S coined the term "Capsistors" for them. Replace all of them. They are usually 4.7uf or smaller. If there is room use a film cap of the same value but 50V. These will be in the list.

The Main Filter caps will be the last to be done, if at all. The originals are still in mine, and running quite well. Hold off on them until after final testing after the recap.
 
When I said orange caps in my post above, I meant the light blue Sanyos, I was testing the old caps from both the 737 and a 780 I was working on! Note that the orange "low leakage" Elna ones from the SX-780 were just as bad as the 737's "low leakage" light blue Sanyos, by the way! On average the three year newer 780's regular caps were only marginally better than the 737 caps.

IIRC, I was short two 22uf 50V caps in the list above and had to pick them up local. It pays to check your boards for what's actually on them BEFORE you order! Also, the relay that they shipped me from Mouser was too large to fit, I have a post at the bottom of the Relay Replacements link that explains it. Must be mis-packaged from Mouser???
 
Hey thanks! I'm getting my parts lists togethor as I write this, The list I just added to my cart from"PIONEER SX-737 REBUILD PARTS LIST 9/16/2016"
didn't have a totals summary (that I could find) so maybe I'll make an updated version with totals for ordering. All the part numbers are still good, the prices all seemed slightly lower than the listed ones (not that it differed much).
Ive been basing most of what I'm going to be doing from your threads, thanks for all the info, it is appreciated!
 
When I said orange caps in my post above, I meant the light blue Sanyos, I was testing the old caps from both the 737 and a 780 I was working on! Note that the orange "low leakage" Elna ones from the SX-780 were just as bad as the 737's "low leakage" light blue Sanyos, by the way! On average the three year newer 780's regular caps were only marginally better than the 737 caps.

IIRC, I was short two 22uf 50V caps in the list above and had to pick them up local. It pays to check your boards for what's actually on them BEFORE you order! Also, the relay that they shipped me from Mouser was too large to fit, I have a post at the bottom of the Relay Replacements link that explains it. Must be mis-packaged from Mouser???

This is good advice I will go through and double check the lists with what is on my boards! I'd like to know what happens with your relay situation, thanks for your help!
 
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