WELCOME to the
Madhouse
!!! A lot of us are retired, and want to re-live our youth.
As for the 737, if you haven't got the manual, get it. It's gonna be your favorite reading material for a while. Bookmark
this link for most anything PIONEER. If there is a Regular Definition and a HiDef version, get the HIDEF. Download everything on the 737. The rest is in no particular order but most of what ican think of is there. There's bound to be more, and others will pitch in. Use an incandescent bulb vs the Halogen. I made mine with a 3way socket, and have a jumper plug so i can preset the wattage on any of the 3 wattages (50-100-150) Works well and I use it on both tube and S.S. gear.
BEFORE ANYTHING ELSE, CLEAN ALL POT's , and SWITCHES with Caig DeOxit. Multiple application cycles may be indicated depending on how dirty the unit is. Test after cleaning. Faderlube after testing and either it's working or not.
In the manual is the amplifier adjustment.
The manual is wrong. See
this thread for the info and incorporate it into your manual.
Do the BIAS and OFFSET checks next. If out of spec, adjust using the upgraded instructions. Then listen for a while to see if the problem still exists then get yourself some transistors
There are some Trouble prone transistors in PIONEERS of that era starting with the x3x series (434,535,636,737,838,939, and the 1010.) The #1 culprit is a transistor in the amplifier, 2sc1451. It's encased in a circular heatsink., One or TWO per channel. The preliminary symptoms are what I describe as Rice Krispies. And it gets worse. The 1451's WILL DIE and when they do pretty much figure on rebuilding the amp board. The 2sc1451 is #1 on the PIONEER FORUM TOP TEN WANTED LIST. It's that bad of a transistor at this age (40+). Replace with the
Fairchild KSC3503.
Tied for the #2 spot on the TOP TEN LIST are kissing cousin transistors. 2sa725 and 2sa726. They are
almost used interchangeably. Same symptoms as the 1451 but not as bad WHEN they DO die. Replace with the
Fairchild KSA992.
The 2sc1312& 1313 are troublesome but not as much as the 2sa725/726. However they are the complimentary transistors to the 725/726, and should be replaced.
FAIRCHILD KSC1845
Check the boards to see if anyone has been in it and recapped it. If not This thread with a list of models with Parts lists will help.
http://www.audiokarma.org/forums/index.php?threads/pioneer-recap-lists-sticky-suggestion.457663/ Don't just order what's on the list. IT needs to be vetted. Copy the list here and request a vetting. Mark the Fixer does electronics repairs on audio gear now as a living and has been at it for going on 35-40 years or more. He keeps regularly updated spreadsheets with BOM lists and can check the parts list here and make recommendations on obsolete or out of stock parts. There are others that can do this but most every list out there on audiokarma in the PIONEER Section originated with MARK.
If no work has been done to it, the best thing you can do for it, is to replace all the troubleprone transistors, and do a TOTAL RECAP. This means EVERY SINGLE ELECTROLYTIC, and any tantalum caps in it (maybe 1 or 2). Including the Main Filter caps, but they can be done last unless they are physically leaking from the vents in the bottom plate of the cap (in the center.). Electrolytic caps today of the equivalent Value and voltage, are 1/4 to 1/5 the the size they were in 1974-76 when the 737 was made. You CAN use film caps in place of most electrolytics that are less than 4uf (old mfd) provided there is room. Film caps tend to get very big over 1uf. But they don't dry out like electrolytics. So if you pass this to your grandkids, they won't need to replace the film caps.
When the need to lift a board comes along, DO NOT EVER UNWRAP the posts the wire i attached to. The wirewrap is a special airfree connection and takes a special tool and a lot of experience to use. UN-BIND the wire bundles, and you'll get plenty of slack to flip over most any board (except the tuner board which will only come up 1/2 way. If the board needs to be removed or changed, then unsolder the actual post from the board, and mark the post/wire 1st. Some posts have barbs on the end to grab the board so be careful you don't rip it out and create a larger hole.
I would start with the POWER SUPPLY BOARD. (Don't forget the Zener Diodes on this board. Just replace them. They take a beating.) Recap and replace the transistors and Zener diodes. New Heatsink grease is MANDATORY for those attached to heatsinks. Otherwise when they heat up they die. Having Clean power of the correct voltage to the amps, and other boards is the best way to start.
Then do the protection board, replace the relay (don't bother trying to clean the contacts, they'll just carbonize in 6 months to a year), RELAY
REPLACEMENT THREAD HERE, then work on the AMPLIFIER board, Tone Control board, and eq boards working backwards from the amp to the inputs. Don't forget the Microphone board. It's connected to the EQ board and can cause all kinds of problems.
Get a can or two of CAIG De-Oxit D5 or DN5, Caig Faderlube F-5. The D5/DN5 is the contact cleaner, and the F5 is the cleaner/lubricant. Just using the D5/DN5 and no F-5 will cause gouging of the carbon track in the pots due to lack of lubricant on the tracks. Then you have a non responsive pot. Basically, if the handle or knob goes in-out, up-down, or Round and Round, it gets De-Oxit. There is a good thread on using De-Oxit for the best results. called
"The Idiot's Guide to using De-Oxit (re-visited)!" Suggest you bookmark all of these threads.
Search function in AK is kind of limited. BUT if you type in SX-737, SX737, SX 737 and have a starting date of 5 years previous you should get a whole bunch of threads on repairs, rehab's, etc. for the 737.
I did my SX-737 in 2013, and used Marks recommendations all the way. What you are hearing now is a tired worn out 737. When you get done you'll have what amounts to a new 737 under the hood. And it will sound VERY MUCH BETTER. I started with a 434 in 75 when I was in the Navy. Lusted over a 737 for the next 39 years and finally got one, after having a 1010, and keeping a 939. My feelings are if you want to keep up or beat the Joneses, go for the 1010 just for the bragging rights. If you are more interested in the sound of the music, the 737 is the best of the bunch. Granted it's 35Watts per channel, but for functional features per $, it beats everything in the x3x series. The 939 is just a bigger 737 with a few changes in features. From my ears they all sound the same. The bigger units have more headroom for big dynamics, but the 737 has some too. It's mid sized so it'll fit almost everywhere, and it'll drive fairly in-efficient speakers, but like with every midsized unit, the more efficient the speaker, the better! And it's a simple well put together unit aesthetically. I use mine with Sansui SP-2500's (98db) and I don't have to crank it up to 4 before the windows are rattling. The one feature PIONEER missed, (and they really screwed themselves here) is the PRE-OUT / MAIN-IN Jacks between the preamp section and the amplifiers. And the ONE Feature PIONEER dropped after using it only on the 737 & 838 was the Recording switch setup on the front so you could record directly from FM or other sources while listening to another. They should have put it on more models.
And one final thing. Pictures here of problem areas are worth more than ten thousand words. So take plenty of pictures, different angles, and with good lighting. But don't get ham handed with the lighting as a lot of detail can be washed out.
So what are you waiting for. Get with it, have fun. Ask questions if you get stuck. AND............................................................................
Larry
and the 2073 in the Q2 slot
. In a hurry, working upside down I made a serious error. I did download the data sheets. For the benefit of all who may read this, be sure you download the data sheets for all transistors. Thank you for bringing up that subject. I switched them out and did the adjustment and readings again. 
. I will hook up some components tomorrow and run it for awhile. larryderouin you had it right!
Thanks! I will post my findings after some playtime tomorrow. I have pics of the rebuild...should I post them?
