Avalon vt-737sp

[pucho812]

well I may have access to that part of a drawing that is the PSU, keep me posted.

 

[Jdm5149]

K. Thanks. I’ve seen the one for the +-34. With 350t off the supply I read normal 5-600 on one pin. But other reads in the 200’s.

 

[Jdm5149]

Replaced c23 with 4700/16v. Voltage starts around 5.5v then after a minute or two it drop to 2-3v. Everything else ok

 

[Jdm5149]

K. Tried tracing from bottom of power supply. Seems it looks like 13 v making it to 350t. Again I accidentally shorted out Q12 (546b). Replaced and now still 2.9-3 v. Also T4 is now reading 12v. It was 68 this morning.

 

[pucho812]

Let me draw you something.
Will take a minute and be sloppy

 

[Jdm5149]

Thanks

 

[Jdm5149]

Well I think I messed up the board a bit. Some pads are totally burnt from all the soldering. I found that c8 was reading 26uf while in circuit. I think I’m finally done trying to repair. I learnt a lot in the process and will continue to look for a power supply. Any suggestions for continuing will be great. If anyone want to try and salvage this supply I would pay

 

[pucho812]

That's a shame. Sorry you had so much trouble.
C8 is part of the 6V line. What vale is in there?
I was about to send you a drawing of the entire 6VDC PSU starting at the KBU6D

 

[Jdm5149]

Send it I guess. Maybe one more try

 

[pucho812]

Check your messages.

 

[chrispbass]

OK, so finally got this on the bench. Quick visual inspection and have a partially melted molex connector from the TX to the board on the heater secondaries. The bridge rectifier is partially shorted, C23 seems out of spec. Aside from that, nothing else looks burnt out on the board. Desoldered the 10 way molex connector, all transformer secondaries seem fine, so I'm going to order a new KBU6D bridge, C23 (4700uf 16v cap) and may get a new LM350T reg to be on the safe side.

As tempted as I am to just solder the wires straight to the board, can anyone please point me in the right direction regarding a mouser part number for the 10 way molex connectors as they're welded together. Will be the male/female housings and crimps needed.

Will pop up some pics over the next day or so.

cheers

Chris

 

[Jdm5149]

I ordered from mouser. 538-39-28-1103. 538-39-01-2100. 538-39-00-0039. 538-39-00-0047. Those were for the molex Diff gauge socket. Think I went with the smaller ones Let me know if these are correct

 

[chrispbass]

I ordered from mouser. 538-39-28-1103. 538-39-01-2100. 538-39-00-0039. 538-39-00-0047. Those were for the molex Diff gauge socket. Think I went with the smaller ones Let me know if these are correct

Perfect, thanks very much for that. I'll order a few of each crimp type to be safe.

 

[Jdm5149]

redid again and was hopeful. Was testing 5.6v then after awhile I tested and it went down to 2-3v. All other voltage correct. Even got 68v at T5. I’m thinking maybe the board might of gotten damaged by all my soldering. I might try and hardwire some pcs

 

[Jdm5149]

Well. Started her up this morning and after letting it sit for a few minutes. Lo and behold. I have 6.29 at T2. Hopefully I have power supply going correctly now. But, still no input with a mic or line in instrument. I see other test points near the preamp. And ideas on values ?? I guess power supply was maybe half the issue.

 

[pucho812]

are the tubes good?
Test and replace.

 

[Jdm5149]

They are all lighting up. K. Gonna have to learn how to test

 

[chrispbass]

Had a couple of hours tonight to have a go at this.

A fair bit of burning around the tx connector.



Desoldered the 10way connector. Unfortunately the trace had lifted, so scraped away any carbon and carefully glued it back down and cleaned it up.



Decided to beef it up by soldering a solid copper wire from the molex to the bridge, but had just finished that then got distracted by a phone call, and when I got back, forgot to take a pic.

Anyway, replaced the capacitor, took out the voltage reg to test…it was ok, but I’d bought a new one just in case, so fitted that.

Had to hack the molex plug to separate it and recrimped the majority of the cables.



Quick test with the power supply cable disconnected from the main board and now all voltages present and correct.

Connected up the signal gen and scope and all good, so hopefully all will be well for a good few years.

Big thank you to all contributors on this thread. @Jdm5149 for pointing me in the right direction with the mouser part numbers and of course, the Avalon whisperer himself - @pucho812.

 

[Jdm5149]

Congrats !!

 

[chrispbass]

Well. Started her up this morning and after letting it sit for a few minutes. Lo and behold. I have 6.29 at T2. Hopefully I have power supply going correctly now. But, still no input with a mic or line in instrument. I see other test points near the preamp. And ideas on values ?? I guess power supply was maybe half the issue.

What voltages have you got with the psu plug disconnected?