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SX-737 Tuner issue

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pa_200

Well-Known Member
I picked up a nice SX-737 and want to change all the old caps and transistors before I give to my son.

After I had a successful work with my other SX-828, we made a kind of sound-/tuner check between these two nice receivers.

Bevor I started, we compered the Tuner of the 828 with the 737. My 828 has got an excellent sound and a very good tuner signal, BUT the SX-737 is very weak on the tuner part. For the comparison we tuned to the strongest local station for both receivers with the same station frequency and the same antenna position, the 828 displayed a strong signal above 4 but the 737 got only to a maximum of 1.5 with the tuning meter centered and the stereo light on.

So I need some help especially for the work on the tuner board.

I tried to find as much information here about the SX-737 but still I am not sure what to do for an improvement.

My initial plan was to use the actual BOM-List for the 737 and change all the parts listed.

Then I saw the information not to touch the C38-C40, otherwise I would change the stereo adjustment.

So my question to Mark, Merlyski, Larry and all the other 737-User would be, what shall/can I to on that tuner board to get the best signal and sound one could get?

I have no FM Signal generator for an alignment, but if I can to it without a special equipment, than let’s try it out.
 
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You can certainly change the electrolytics on the Tuner board. They won't mess with the alignment. And that includes C38-39-40 which are most likely Sky Blue Sanyo CSSA types. These are Solid Aluminum caps that breakdown and have increseed resistance. Echowars coined the term.."Capsistors" for these things. Use Nichicon UKL Series caps for these.

My 737 only pulls a max of 1.5 on the meter even with a 50Kw station 5 miles from the house. It should blow the meter out of the cabinet...
 
Some other issue beside the tuner because I will do all the other boards as well.

I did some DC voltage testing on the other boards and ended up at the Main Amp. When I touched the heat sink of the Q7 I got a voltage reading, the same on all three others Q8 – Q10. These are the 2SD357 and 2SB527. What I got there was the collector voltage what I didn't expect. So there was a direct contact between the transistor and the heat sink! But only on these four, all other heat sink have been isolated. Is that OK for that special position or what's your advice?

My initial plan was to change the Q1 - Q6 as well, so my question to you, what shall I do with the Q7 – Q10? Change as well and isolated the heat sink with a proper mounting kit or leave theme as they are?
Just in case one of you recommends a change on the 2SD357 and 2SB527. Which ones are the best replacement for the amp board on the SX-737?
 
Q7 thru Q10 have heatsinks electrically ISOLATED from the board. They DO have Collector voltage on them. This is NORMAL as on some designs the collector voltage is taken off the back of the transistor. You can certainly put a TO-220 ISOLATOR KIT on each of them or leave them be and just renew the grease.

Here's the list of Transistors for the AMP board and the outputs. These are all Mouser Numbers and are all currently in stock.

AWH033 q1 2sa726 512-KSA992FBU
AWH033 q2 2sa726 512-KSA992FBU
AWH033 q3 2sa726 512-KSA992FBU
AWH033 q4 2sa726 512-KSA992FBU
AWH033 q5 2sc1451 512-KSC3503DSTU
AWH033 q6 2sc1451 512-KSC3503DSTU
AWH033 q7 2sd357 512-KSC2690AYS
AWH033 q8 2sc357 512-KSC2690AYS
AWH033 q9 2sb527 512-KSA1220AYS
AWH033 q10 2sb527 512-KSA1220AYS
AWH033 q11 2sd370 863-MJ21194G
AWH033 q12 2sd370 863-MJ21194G
AWH033 q13 2sb530 863-MJ21193G
AWH033 q14 2sb530 863-MJ21193G
 
Thanks’ Larry for your list, much appreciated.
I’m not an electronic or tuner specialist, so I have to work my way through the machine with every help I can get.

My first work on a Pioneer was the SX-828. It came to me in a very bad condition and running only on one channel. Whithout making a longer tuner test or checking the sound, I just started to renew all the major boards, beginning with power supply and finishing with the power amp.
All the work was done with the help of the available BOM-lists for the 828 at AK.

At that point, when I worked on the tuner board, I didn’t even think about FM, MPX or Stereo Alignment, because I just changed the listed caps and transistors. Actually I had no idea what will come out at the end, when everything I could do, was done on every single board.
So it was a very impressive moment after the first power up, to listen to that excellent clear and precise tuner reception and warm sound of that receiver, what I never expected at all.

But that was the SX-828 and now I have the 737 in front of me with the limited tuner reception and sound at this stage.
Maybe I’m lucky a second time and all the new parts will help to improve the two issues I have right now. If not, I will ask for some more help.

But be sure, I keep you informed about all the work and if there is any additional help or advice out there for that particular Pioneer, feel free to write it down for me and all the other SX-737 user.
 
Thank you for the link, I will have to look for the correct cleaning stuff.
I made some pictures from my VC and it looked quite good so far. Maybe one of you can give me a hint if he can so a few spots that need that treatment.
Don’t wonder with the cut cable on pin 29. I dismantled the AM antenna, because we won’t use it any longer.

IMG_20190729_193740.jpg IMG_20190729_211610.jpg
 
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