Pioneer SX-737 - Original Owner

Well... I've been lurking on AK for several years and have been lusting after my old gear from the '70s. I've picked up a Sherwood S7100 and a Pioneer SX-1050 over the last couple of years. They both work and neither have ever had any work performed on them. But my pride and joy is the SX-737. I purchased it new from Pacific Stereo in Sacramento, CA in 1974 when I was 16. It got me through high-school and college and then I sold it to my Dad for the cash to rebuild the tranny on my first car.... a '67 Mustang GTA fastback. Pictures of car and 737 attached.

I still have the car, restored to showroom condition. And I've been recently reunited with my old SX-737 after 38 years. My goal is to make her purr like new. I re-lamped her and performed an alignment and she sounds and looks great. Only problem is I can tell she's tired and maybe jealous of the car. Her left channel goes out after a few hours of use which indicates a thermal issue. So I bit the bullet and ordered all the parts from Mouser (thank you MTF!) and they will show up next week. If I'm successful with the 737, I'll move on to the 1050.

I'll be sure to take shots and post my findings as so many others have graciously done. I'm a ham radio operator and can find my way around schematics and am able to use the tools. So hopefully I won't be asking too many dumb questions. But I did notice on the re-cap list it doesn't include the two main power supply caps. Anybody know of a current replacement that fits in the brackets? I may not need them, but I'd like to know if someone has experience with ones that fit in the event I do.

Thanks in advance and thanks for being here... and wish me luck!

Craig
 

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Craig; When I did mine 2 years ago, I installed 10K uf 50V Nichicon 647-UVZ1H103MRD in the can's. Used a piece of the 1" gray pipe insulation (look like pool noodles) from Home Depot to shim them in the clamps. You can also cut the original Elna's about 1/2" above the bottom, and stuff the new caps inside, Silicone caulk(clear) the can's back together, and put them back in the clamps. the Nichicon's are 1" x 2", so considerably smaller physically than the originals.

https://www.mouser.com/Search/Produ...RDvirtualkey64700000virtualkey647-UVZ1H103MRD Current price is $4.14 ea.
 
Craig; When I did mine 2 years ago, I installed 10K uf 50V Nichicon 647-UVZ1H103MRD in the can's. Used a piece of the 1" gray pipe insulation (look like pool noodles) from Home Depot to shim them in the clamps. You can also cut the original Elna's about 1/2" above the bottom, and stuff the new caps inside, Silicone caulk(clear) the can's back together, and put them back in the clamps. the Nichicon's are 1" x 2", so considerably smaller physically than the originals.

https://www.mouser.com/Search/Produ...RDvirtualkey64700000virtualkey647-UVZ1H103MRD Current price is $4.14 ea.
Great idea larryderouin! I've done that when re-capping my old zenith console radios from the 1930's to preserve the look. Don't know why I didn't think of it.
 
Performed an alignment???? Do tell....
Mark, I should have been more clear. Aligned the tuner per the service manual. Minor tweaks to the FM section only using my FM SG (Rohde & Schwartz CMS52). Didn't touch the MPX section since I don't have a multiplex signal generator. It seemed to be fine anyway. I did get the caps and transistors to redo the tuner board but I am hesitant to do it given the lack of an MPX SG. Thoughts?
 
Go ahead, on this stereo decoder the only multiplex adjustment is center frequency of the VCO for the PLL. Don't need to set separation or carrier rejection. You have the equipment for the rest, - you didn't mention what distortion analyzer you used to set the FM...

IF no distortion analyzer to set the mono FM, there may be a few caps to avoid. Lower distortion levels (>1%) can't be set (usually) by ear.

The VCO can be set reasonably close by hand while receiving a stereo broadcast, finding the turn ON point (stereo light) for clockwise and turn ON point (stereo light) for counterclockwise and mechanically splitting the difference - IF you don't have a frequency counter. If you have a freq counter, set the VCO while OFF STATION with no stereo reception. All that Lissajous pattern stuff was written in pre-frequency counter time.
 
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Thanks Mark. I don't have a distortion analyzer, but I do have a freq counter. Given this, which caps should I avoid?

Thanks
 
main caps

Hi

I have been using 10k 80V Panasonics which drop straight into the clamps, digikey part P10646-ND

Peter
 
Status Update: Power Supply restoration

I finally got around to starting the restoration. Caps and transistors received from both Mouser and Digi-Key. Even built a Dim Bulb Tester. Pictures of all attached. It took me about 3 hours to go through the power supply and it came back up fine on the DBT and then I heard the satisfying click of the protection circuit. After connecting direct to line voltage, DC voltages at pins 13, 14, 15, 17 and 19 were -13.7V, 34.7V, 30.3V, 22.6V and 13.1V respectively. All good.

I found that a few of the foil pads around the diodes D1, D2, D3 and D4 took a bit of a beating when removing the old ones. Got some pad lifting that I wasn't happy with. I ended up leaving the leads long on the replacements so I could reinforce them by also soldering to another pad on the same trace. Picture also attached. Lesson learned.... make absolutely sure as much solder as possible is off the pad before trying to remove the component. This is a bit tricky since too much heat can cause the pad to lift too!

Something else I learned. I got a little too confident by taking out multiple capacitors at a time and almost put the replacements back in the wrong location. Thankfully I had the service manual with the board layout. In the future, I will do these one at a time.

Thank you MTF for a great service in pulling together the parts lists. I see that C7 on this board is an axial capacitor but the replacement part on the list (647-UPW1H102MHD) is radial. Works fine but sorta looks strange. Stands up instead of laying down. Was there not a suitable axial version? No complaints... just thought I'd ask.

Perhaps I can complete the Protection Circuit and Power Amp this weekend. I'll be listening to my Sherwood S7100 while I work on the SX-737. No need to rush!
 

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The TVX series is axial. It's not a low impedance type like the UPW's used. It won't hurt anything using the UPW, but like you said it does look a little strange sticking up.

Looks good so far. Good lessons you learned. Don't beat yourself on them, we've all BTDT. Take it one board at a time, one component at a time.

A little superglue on the back of any pad that lifts will hold it down enough to solder the piece back on with a little bit more bent over for support.

If your iron is adjustable, raise the heat up some more. Then start counting. If you get to 1000 and 3 and the solder has not liquified, either your iron is not hot enough or you need some added flux or tinner on the joint. Get some Rosin Flux, and for your iron, Radio Shack Tip Cleaner/Tinner. Wipe the tip on a damp sponge, then dip in the tinner rolling the tip in the puddle. Then add a little solder to the tip. Now try the heat/count again. It should liquify by 1000-3 for a normal PCB joint. Have your varaint of solder removal handy. NO MORE THAN a 1000-5 count on a joint at a time and then let it cool down for a minute. But sometimes no matter what you do the pad glue will let go and the pad will lift. Just be prepared for it. SANSUI boards are the worst. Just look at the board and pads start lifting in surrender.

Jsut go slow and methodical. It'll be done before you realize it.

Larry
 
Protection Circuit - AWM-025 - Issue and Question

Caps C1 and C2 on this board are electrolytic 0.22uf 10V but the replacement caps per the "list" (598-DSF050J224) are not. Does this matter in this application? Will work on transistor replacements in the meantime.

Also, the replacement relay is physically different in size and won't fit through the chassis cutout. I'm sure I could find a way to mount it but since the original is working fine and the contacts appear clean, anybody see any reason that I shouldn't just leave it.

Thanks!
Craig
 
The replacements are Film caps. They actually work better than lytics. In sizes below 2.2uf replacing an electrolytic with a film, makes a lot of sense from physical size, and the fact that film caps have no electrolytic fluid to dry out. BUT there are limitations in some circuits where an electrolytic can't be replaced by a film. I haven't learned the in's and out's of the different circuiits and where a film is better than a lytic, so I go with what Mark tells me. He ain't been wrong yet. Also they DO sound better than an electrolytic. As you do more units in the pioneer lines, you'll find that film caps will replace a lot of 'lytics in the smaller sizes. As you go up from 2.2uf films get BIG real fast. So size does matter in some cases here.

If you remove the case from the old one, the new relay should fit very snugly in the old case. I did it in my 737 and 939. You almost have to force it in the case, it's that snug, butit will work. OR look up the "mod" for the realy mounting that MTF and echo came up with using standoff's.
 
Protection Circuit - WOW!

I've finished the Protection Board, changed all transistors and capacitors except for C1 and C2 per my question in the previous post, and WOW! The protection relay clicks about 1 second after powering up. It used to take about 3 seconds. It's been so long since it was new that I can't even remember if it was ever that fast.

Next stop in this odyssey will be the Power Amp
 
Thanks Larry

Good info on the caps, Larry. I'll replace them with the films.

Regarding the relay, the replacement (653-LY4F-DC24) is substantially larger than the original by about 50%. The pin orientation is slightly different as well. I've attached a photo of the replacement relay in proximity to the original. No way could the mechanism be stuffed inside the original housing.

Thanks,
Craig
 

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Happy Protection Circuit

Done w/pics for your viewing pleasure. Thanks Larry for the advice. I'll look into the relay "mod" over the coming days.

Thanks,
Craig
 

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Hold on let me check and see which one I put in mine. Found it. Here's the part #. MY4-02 DC24. This is the recommended one for SX-737,838,939, 1010. I've replaced the original OMRON relays in my 737 and 939 with the MY4-02 DC24 absolutely no problems. They fit in the original case but tightly. The MY4S-02 DC24 is not carried. It would have the bottom mounted bracket on the case and would be the exact one needed. So we make do with the top bracket and standoffs or stuff the original case if you really feel wooly.


The 653-LY4F-DC24 Datasheet http://www.mouser.com/ds/2/307/ly_dsheet_gwj002-e2-10-48034.pdf

MY4-02-DC24 Datasheet http://www.mouser.com/ds/2/307/MY4-02-272832.pdf
 
Also recheck the timing on the click of the relay on the unit. Typical timing is around 4-7 seconds. If it's 1-2 seconds the timing circuit is off and not allowing enough time for the amp to settle down. You'll need to replace, I believe it's C-6 and Q-7. But don't change until Mark verifies the parts. If you already have check pin polarity on the cap, and pin orientation on the transistor. KSC2690AYS replaces Q-7.

Also Add a 1n4007 across pins 9 and 10 on the protection board. Cathode(band) to Pin 10. This keeps the reverse voltage from breaking down the transistor when turning off. PIONEER did this in later models.
 
Thanks Larry.... I will be away from the project for a couple of weeks while on business. Actually it will be good so I get a fresh set of eyes on it. I took pictures of my work as I went along and I can now see I have orientation issues with Q1 and Q2 on the protection board. It seems the pin orientation on the replacement isn't exactly the same as the original. New lesson learned: Never assume the replacement pin configuration is the same as the originals. The Data Sheet is your best friend. Read it early and often!

I'll put the 1N4007 on the board as you suggest. I also ordered the relay you suggested from Mouser. Should be here by the time I am ready to continue.


Thanks,
Craig


Sent from my iPad using Tapatalk HD
 
But my pride and joy is the SX-737. I purchased it new from Pacific Stereo in Sacramento, CA in 1974 when I was 16.
Craig

That's great that you still have your first receiver after all these years. You made a good choice. I really like the SX-737. Just out of curiosity, what speakers did you match with it when you bought your 737?
 
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