Pioneer SX-737 Re-Cap

Larry, I saw your #3 post above with good advice on how to start the process and was looking for more details on what order to tackle the remainder of the boards, as well as how to best gain access.

Is this a good place for this request or should I start a new thread?

Or perhaps there's already a good thread on the topic?

I have to say I'm skittish about desoldering wire wrap pins. Seems like a lot of heat stress on the board that might lift a trace and in some cases the insulation of the attached wire is so close to the pin, I see it could melt.

Thanks.
 
In the mean time, a question about the power amp board (AWH-330). Transistors Q5 and Q6 are originally 2SC1451 being replaced by
512-KSC3503DSTU. The originals have a metal ring on the can, like a heat sink, but the part number is stamped on the ring so it appears that the ring is part of the transistor. The replacement is a 220 style, but no heat sink is called for. Is okay?
 
No problem with the TO-220. If you feel better with a small heatsink on the 3503, go ahead and put one on. I've never put one on the 3503's in my units and haven't had a failure in 8-9 years.
 
Is there an updated part list? I'm planning to do it on my 737! :D And what should I replace? Anywhere to start from or should I just go ahead and replace everything on the list?
 
Here's my latest as of the end of February.
Notes:
I cannot guarantee that Mouser has all the parts in stock.
The big filter caps are not listed.
Although the parts for the tuner are listed, most of us don't touch it unless we have the knowhow and the gear to do an alignment. That said, some have had success replacing the electrolytics and no alignment was needed.
Do a board at a time and test before proceeding to the next.
Use a DBT.
When the unit is apart, BE VERY CAREFUL WITH THE DIAL POINTER. It's very delicate and easy to break off.
When in doubt, ask. When you're sure, ask anyway.

Good luck.
 

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  • SX-737 BOM NEW FORMAT 2.27.zip
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Dim Bulb Tester or a Series inline Light Bulb. Google Dim Bulb Tester and you'll get all kinds of ideas on how to build one. If you have a junk box with a light switch, an outlet, and a ceramic lamp socket, you've got 99% of the DBT right there. All you need is an extension cord you can cut the end off of, and a couple of gang boxes. I put a 3way lamp socket on mine and use a 50-100-150 bulb as i use it for Tube gear also. With the 737 a 100W bulb will give you good results. Make sure it's an incandescent as an LED won't limit the current (amps).
 
First question! What about those wire wrap? Do you guys unwrap them to take out the circuit? Unsolder the pin? Or work on the board while it's in the amp itself?
 
I hope I'm asking this question on the right thread. On my Pioneer SX 737, my amp board has C1/C2 using 4.7T/25V, instead of 0.33uF as shown in the SM and on MTF's list. They are two little blue dots, and I measured them at about 5uF each. Also my C1 /C2 are rotated 90° from anything I've seen. Perhaps my board is a very old or the very last version of production for the Pioneer SX 737. I've recapped everything and changed all the transistors except for the tuner board, where I did a full recap but only changed the two recommended transistors, Q8/Q9. DC offset and idle current adjusted to SM specifications..... the sound is spectacular.
My question for my amp board is 1)are those tantalum capacitors? 2) should I just change them to the 0.33uF wima, or just use electrolytic caps at 4.7uF each for C1/C2 to match what was on the board? Those little blue Capacitors look like they came from the factory that way as the solder joints looked undisturbed.

Kindly looking for advice.

Thanks.

Tony
 
https://audiokarma.org/forums/index.php?threads/pioneer-tuning-fork-service-guide.249745/

See in the above thread Post #11 first attachment of 'capacitor' series of Tunng Fork images of classic Tantalums. I think go with the value that's on the board. If you're talking 4.7uF is what's in there -- WIMA 4.7uF in long leads can be had -- I just put some in a Sony STR-7045 -- if there's room -- the following are 7.2mm by 7.2mm. 505-MKS2B044701KJC00 C1/C2 that's a coupling cap no? So you might go with a nice film cap like the aforementioned WIMA, if you can fit 'er in there. There's other film caps. Other folks might have other ideas. Yes the Pioneer SX-737 a sweet soundin' machine 'n' purty, too. Cheers.
-Matt
 
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Would it be beneficial to replace SX-737 two 6800 uF filter caps with 12000 uF?
Can that hurt anything?
 
Having a reasonably greater number of electrons than factory spec loafing to be called upon can be beneficial I think however caps that are too much larger than factory spec can mean a greater-than-healthy current inrush on power-up. From what little I understand. Just a guess but sounds like too much of a bump.
 
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Thanks.
I was not clear posing the question, of course I meant to replace both caps: 6800 uF to 12000 uF.
 
Maybe pose the question whether you should leave what you have in there. Or if you want to replace whether there is something like a long hour high ripple rating maybe 8200uF 63V drop in, or easily adaptable, recommended substitution, where you could leave the factory rectifiers in place. Someone might have an idea.
 
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Ok, maybe better formulated question is this:
How do I know if power supply filter caps (and others as well) need to be replaced?
Measuring capacitances of filter caps (and the 1000 uF one) with DVM showed values greater than nominal but is this a good enough check of the health? Should they all need to be replaced no matter the measured values are?
 
age and future (un)availability guide most choices.

if one cap of a group shows higher AC ripple (dc blocked reading), the group gets it.... (i.e. the others aren't far behind)

justification for age replacement:
an electrolytic cap is a conglomeration of chemistry reactions internally, approximating what we call a capacitor.
chemistry "wears out" eventually, conforming less and less to expectations
So it may grossly measure ok, but start looking for the edges of the performance envelope, and they'll be worse than you expect.

long complex electrolyte formulas are evidenced by the "capacitor plague" when industrial espionage
swiped a great new electrolyte formula, which then showed up all over the place.
but, these caps failed early, vented, exploded and did all kinds of mayhem.

It is strongly surmised that the full formula covered two pages, and the second page was lost. The rest is history - popping caps.

an interesting failure symptom is the measurement of capacitance showing up to 100% excess value, and fluctuating with temperature.
the other would be fluctuating electrical leakage current.

I did a phono preamp with good UPW caps on one side in the "low noise" specified component positions and UKL's (special low leakage caps) on the other.
Leakage translated out into increased background noise. It convinced me....
 
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