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I'm a noob - SX-737 Rebuild (follow along?)

YoSeth

YoSeth

New Member
Ok, so not a total noob. A few years ago I successfully replaced all the 2SA725s and 2SC1313s. Decided to carry on and do a full recap since nothing else has ever been touched. I purchased the recap kit from eBay and opened her up today, starting with testing the output transistors per the kit's recommendation. The output transistors read:

2SB370 - 358kohms
2SB530 - 330kohms
2SB370 - 337kohms
2SB530 - 329kohms

It appears they are all bad and should be measuring at least 900k. Placing my mouser order now!
 
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Bipolar Junction Transistor Testing Basics

Get a lot of Q's on this, so I thought I'd put together a post. First you need a decent digital meter with a diode test function. Forget about using the ohmmeter part of your meter, it is way too unreliable for this. Almost all digital meters nowadays have a diode test included, and it is...
audiokarma.org
 
Hi again! After a long break, I began the rebuild. I started with the protection board. Didn't have any issues replacing anything. But I hooked her up to my Dim Bulb Tester and the bulb glows very bright. And the receiver doesn't power up on the DBT. So....Where should my troubleshooting start?

BTW: my DBT has a 100w bulb. That'll suffice, right?
 
75 watt would be better until you get use to using the DBT.
Start by looking over all the work you did. Solder bridges?
If all you did was the protection and it was working before you tackled it, I would check Q6 and Q7 for installation correctness.
Pull fuse F2 and F3, see if the set lets the DBT dim. That would be a clue to the Protection board causing issues.
 
zebulon1 said:
75 watt would be better until you get use to using the DBT.
Start by looking over all the work you did. Solder bridges?
If all you did was the protection and it was working before you tackled it, I would check Q6 and Q7 for installation correctness.
Pull fuse F2 and F3, see if the set lets the DBT dim. That would be a clue to the Protection board causing issues.
Click to expand...
Thanks. I tried a different bulb and got some usable results. The receiver now powers up, and the bulb glows bright briefly before becoming dim. But the receiver lights flicker a bit and I don't hear the relay engaging.
 
Check your amp settings.
Dial the Idles down to zero. Dial them up and back down making sure they respond to the trimmers.
Set the DC balance. Set them to Zero volts.
You can’t run the receiver on the DBT. It will get strangled without the correct current. Volume at min, balance knob at center.
You can check the amp settings and the power supply voltages.
Make sure the idles are at zero before you remove the receiver from the DBT.
If the bulb was dim and the amp can be adjusted, the PS voltages are good, go to full line voltage and set the idles to service manual for the last time.
 
zebulon1 said:
Check your amp settings.
Dial the Idles down to zero. Dial them up and back down making sure they respond to the trimmers.
Set the DC balance. Set them to Zero volts.
You can’t run the receiver on the DBT. It will get strangled without the correct current. Volume at min, balance knob at center.
You can check the amp settings and the power supply voltages.
Make sure the idles are at zero before you remove the receiver from the DBT.
If the bulb was dim and the amp can be adjusted, the PS voltages are good, go to full line voltage and set the idles to service manual for the last time.
Click to expand...
Was about to check the idles when I smelled something and noticed a little smoke near one of the output transistors. Quickly unplugged everything and noticed the transistor near where the smoke was coming from was sitting crooked on the heatsink. I took it out and reinstalled correctly. But now, is doesn't power on at all and the bulb is very bright. So....where do I go from here?
 
Does it power on or powers on and stays bright in DBT?
Shorted outputs (maybe) and some resistors i guess. Did you check if the mica insulator for the outputs is not cracked. Pull all outputs and test them one by one. Reinstall with new mica insulator and thermal paste. Test all the emitter resistors/driver transistors
 
soccerfan said:
Does it power on or powers on and stays bright in DBT?
Shorted outputs (maybe) and some resistors i guess. Did you check if the mica insulator for the outputs is not cracked. Pull all outputs and test them one by one. Reinstall with new mica insulator and thermal paste. Test all the emitter resistors/driver transistors
Click to expand...
Doesn’t power on at all
 
I have yet to see a mica behind the opt transistors unless the output's have been changed on the x3x series PIONEERS. Pioneer used some kind of clear insulation spray or dip on the heatsinks and attached the transistors directly. Best practice is to remove OPT's 1 at a time and wipe down the heatsink area behind OPT with Acetone to remove the insulation, then standard practice of Heatsink grease and mica's (grease both sides very lightly (opaque layers), then attach OPT with screws, ensuring screw is centered in hole without touching sides. Other than that mod, go with what YoSeth said.
 
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