Avalon VT 737 sp

[TheseGoToEleven]

they all have about 71 restistance except for 64 and pin 9 of K9 am readin 20ohm

Ok, what is the resistance between 64 and pin 2 of K8?

 

[punkt]

a

Ok, what is the resistance between 64 and pin 2 of K8?

also 20

 

[TheseGoToEleven]

also 20

Ohms or kilo Ohms? How about a picture of the meter when you are measuring between 64 and pin 2 of K8. And another picture measuring between T12 and pin 2 of K8.

 

[punkt]

Ohms or kilo Ohms? How about a picture of the meter when you are measuring between 64 and pin 2 of K8. And another picture measuring between T12 and pin 2 of K8.

meter is set to 200k like always

 

[TheseGoToEleven]

Ok so the meter is showing 69.9k between T12 and pin 2 of K8. But on the other measurement, the probe is not on 64, it is somewhere else. I have circled 64 in the pic below. Measure again between 64 and pin 2 of K8.

 

[punkt]

Ok so the meter is showing 69.9k between T12 and pin 2 of K8. But on the other measurement, the probe is not on 64, it is somewhere else. I have circled 64 in the pic below. Measure again between 64 and pin 2 of K8.
View attachment 147385

It’s zero

64 and pin9 of k9 are also 0

 

[TheseGoToEleven]

It’s zero

64 and pin2 of k9 are also 0

Ok that's perfect. The signal path through the relays to the Output knob looks good. I really wish the bottom of the board was labeled like the top. That would be SO NICE for doing repairs.

I don't know why it is showing 69.9k ohms between T12 and pin 2 of K8. I thought that should be zero but maybe there is some part in between that I'm forgetting, and I don't have a good unit here to check that. Do you have any pictures of the bottom of the motherboard with the tube card removed?

If not, then turn on the unit and let's go back to checking AC voltages at T12, 64, 63, and T15. Hopefully now we see audio signal reaching them all.

 

[punkt]

Ok that's perfect. The signal path through the relays to the Output knob looks good. I really wish the bottom of the board was labeled like the top. That would be SO NICE for doing repairs.

I don't know why it is showing 69.9k ohms between T12 and pin 2 of K8. I thought that should be zero but maybe there is some part in between that I'm forgetting, and I don't have a good unit here to check that. Do you have any pictures of the bottom of the motherboard with the tube card removed?

If not, then turn on the unit and let's go back to checking AC voltages at T12, 64, 63, and T15. Hopefully now we see audio signal reaching them all.

i got u in the meantime i will get it ready to test it with ac

 

[punkt]

Ok that's perfect. The signal path through the relays to the Output knob looks good. I really wish the bottom of the board was labeled like the top. That would be SO NICE for doing repairs.

I don't know why it is showing 69.9k ohms between T12 and pin 2 of K8. I thought that should be zero but maybe there is some part in between that I'm forgetting, and I don't have a good unit here to check that. Do you have any pictures of the bottom of the motherboard with the tube card removed?

If not, then turn on the unit and let's go back to checking AC voltages at T12, 64, 63, and T15. Hopefully now we see audio signal reaching them all.

no readings on 64,63 t12 still at bout 4 and t15 at 1

 

[TheseGoToEleven]

i got u in the meantime i will get it ready to test it with ac

Ok, that photo isn't sharp enough for me to see the path between T12 and the relays but it's great to have it here anyway. Should help someone else in the future.

 

[TheseGoToEleven]

no readings on 64,63 t12 still at bout 4 and t15 at 1

Ok, so the signal still doesn't reach 64 even though the path through the relays is good. It seems the signal at T12 is getting killed going through the 70k of resistance between T12 and pin 2 of relay K8. If there are really no parts in between (I don't have a schematic) then it would have to be a problem with the trace itself, the T12 pad, or the soldering.

@pucho812 Any idea where the 70k of resistance might be coming from?

 

[TheseGoToEleven]

no readings on 64,63 t12 still at bout 4 and t15 at 1

You could try reflowing the solder on T12. Maybe the red wire and the PCB trace are not connecting properly through the T12 pad. Couldn’t hurt.

 

[punkt]

I uploaded the Picture right from my phone, this should help with the details

 

[punkt]

he

You could try reflowing the solder on T12. Maybe the red wire and the PCB trace are not connecting properly through the T12 pad. Couldn’t hurt.

WE DID IT GUYS, i reflowed it and it works again

 

[TheseGoToEleven]

WE DID IT GUYS, i reflowed it and it works again

Bravo! Now if you still get weird noises when you press the phase button, I would suggest replacing K2 on the motherboard, under the 7372 card, since you already bought some new relays.

 

[punkt]

Bravo! Now if you still get weird noises when you press the phase button, I would suggest replacing K2 on the motherboard, under the 7372 card, since you already bought some new relays.

Thank you so much for your patience and time, can i send you some coffeemoney over paypal?

 

[pucho812]

Solved.
Brilliant.

 

[TheseGoToEleven]

Thank you so much for your patience and time, can i send you some coffeemoney over paypal?

All good! Glad it is solved and hope this time it is a lasting fix. It looks like you had at least one bad relay, but before the signal could even get there, it was getting killed by a bad solder joint at T12.

Just for fun here is a picture of the bottom of the 7372 line level I/O card with component labels added. Might come in handy for someone reading this thread later, but hopefully you'll never need it!

 

[punkt]

All good! Glad it is solved and hope this time it is a lasting fix. It looks like you had at least one bad relay, but before the signal could even get there, it was getting killed by a bad solder joint at T12.

Just for fun here is a picture of the bottom of the 7372 line level I/O card with component labels added. Might come in handy for someone reading this thread later, but hopefully you'll never need it!

I really hope our diagnosing helps people in the future,

 

[pucho812]

so take away was joint went bad/cold. in turn doing so caused to go HR, high resistance. that's where the 70K come from would be my guess. You guys are so smart and sadly I can't always be around to answer questions.
rock on.