Avalon vt-737sp

[chrispbass]

@Jdm5149 I’ll have the unit here for a week or so, so happy to open it back up and take a few readings etc

 

[Jdm5149]

178. 12. +\- 34. 6.29. Pretty much all good. Connected I have the same. Also +\-34 at other suggested points. I see other test points near the preamp gain pot. I just ordered a new set of tubes so that’s next. Will get back to guys end of week when they arrive

 

[pucho812]

You can run the unit with 3 tubes if you don't use the compressor. The other tubes have to be in place though for it pass signal.
From left side of chassis to right it's preamp tube, eq tube, output tube and compressor tube.
Also check the following 5600-7372 card. I think that is the correct card number. it is the one to the left of the PSU chassis. Check it for any failures. recap the 100UF/50V(blue vishay) and 10uF/63V(blue vishay)to extend life of your unit. I usually recap them with Panasonics even though they are not the same footprint, they work well. Come to think of it, that should be done on the eq and compressor cards too.

 

[Jdm5149]

K thanks a lot. Will do

 

[Jdm5149]

I see a T1 on the I/0 board. Should I be getting a reading there. No voltage detected there. I have +/-34 and 14 volts on those top two resistors but really don’t. Know what to test for on that board. Caps were reading high uf when connected but good taken off board.

 

[Jdm5149]

K. Tubes arrived and still no signal. My 6volts was still giving problem. Fluctuating but tinkering around d4 and r11. I think the circuit board pads might be a little suspect. Maybe a cold solder but after tinkering now I have a solid 6.29-6.30. But still no signal. Starting to think that it’s also the i/o card but only see one test point. It reads 0 volts. I get the +/- 34 and 14 volts at those two resistors on top that are always mentioned. The caps and transistors seem to test ok. Only think I saw was when testing caps in circuit they tested high uf. Off the board they tested good.

 

[pucho812]

Hmmmmm.
T1 is most likely for dc offset and uses the trim pot. You should see some signal there unless it was trimmed flat as it should be.
If we test solder point t1, t2 and the others on the main board in reference to ground, what do you get?

 

[Jdm5149]

I will try again tomorrow. But this morning it was T1 179v. T2 6.2v T3 .0056v T4 69v

 

[Jdm5149]

+/-34 good at all mentioned points in prior posts

 

[TheseGoToEleven]

I marked up some photos when I worked on one of these units a while back. Hope they are some use to you for tracing input signal once the power rails are sorted.

 

[pucho812]

+/-34 good at all mentioned points in prior posts

Ok.
Did you replace 10uf and 100uf lytics? They are the blue ones all over the unit.
Recap the input card

 

[Jdm5149]

K. Thanks again. They were reading high in circuit. But off they were testing good. I will try again Friday. Thanks for your help. I will test those points tomorrow

 

[Jdm5149]

No voltages at any of those test points. I get 93v on those orange caps in the middle two points. The outer two points read 0v. The bottom one reads 100v on the right side and a negative small reading on the left. I’ve read on prior posts about replays going bad. Where are those located

 

[pucho812]

Why are the orange caps there?
That’s not standard Avalon at all.
Every switch triggers a relay.
It’s what the 12v from the PSU is for.

 

[Jdm5149]

This is the underside. Should I be reading any voltages at those test points. Maybe TheseGoEleven has a larger pic

 

[pucho812]

Why are the orange drop capacitors installed? That is not factory. Why were they installed?
I am also seeing non factory pots installed. And that yellow cap is also non factory.
Did you install any of that?

 

[Jdm5149]

No. Those pots were definitely put in. In fact it is pushing up on the vu adjustment pot. Gonna replace those after unit is working. I see someone wrote that it was worked on in 2021. All of this was the way I got it

 

[TheseGoToEleven]

Why are the orange caps there?
That’s not standard Avalon at all.

I was wondering that too. Some kind of mod? They were not there at all on the unit I worked on.

 

[TheseGoToEleven]

Here is a larger pic of the underside. The vertical board that houses the push buttons for "high gain", "phase", etc will send a +12V DC or 0V signal to the corresponding relays via the colored wires. I don't remember which wire color matches with each button but you can find out by experimenting.

 

[Jdm5149]

Yup definitely not like mine. K will rest in a bit again. But I think I couldn’t get any voltages from any of those T points