Avalon VT 737 sp

[punkt]

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.

i have to ask if this was just a bad quality control issue, because the unit didnt got repaired before, and i didnt touched t12, but am happy it's finally solved and i hope it stays that way, i feel like i can open up a repair shop now hahaha just kidding, was a great learning experience tho

haha all credits go to @TheseGoToEleven i just followed your instructions, i was reading all the other threads and also the pdf with the notices from @TheseGoToEleven but i really couldnt could wrap my head around

glad forums are still a thing in these ages of the internet, used to hang out alot in my teens in diverse forums

 

[TheseGoToEleven]

i have to ask if this was just a bad quality control issue, because the unit didnt got repaired before, and i didnt touched t12, but am happy it's finally solved and i hope it stays that way, i feel like i can open up a repair shop now hahaha just kidding, was a great learning experience tho

Well you know a lot more about things that can go wrong in that unit now, that's for sure. I don't know anything about their QC but I don't remember seeing any previous Avalon posts with bad solder joints. Maybe it could have been a break in the wire too, but close enough to the joint that another soldering fixed it. If it happens again, then maybe try replacing the wire.

glad forums are still a thing in these ages of the internet, used to hang out alot in my teens in diverse forums

This one is good and seems surprisingly busy for something so specialized.

 

[punkt]

Well you know a lot more about things that can go wrong in that unit now, that's for sure. I don't know anything about their QC but I don't remember seeing any previous Avalon posts with bad solder joints. Maybe it could have been a break in the wire too, but close enough to the joint that another soldering fixed it. If it happens again, then maybe try replacing the wire.


This one is good and seems surprisingly busy for something so specialized.

We back at it, when pressig EQ>COMP , the Signal gets turned down by more than 40dB, gonna open up it up again later.

Doesnt matter if Comp or EQ are switched on or off, as soon as I press EQ>COMP the signal gets turned out by a large amount.

 

[TheseGoToEleven]

We back at it, when pressig EQ>COMP , the Signal gets turned down by more than 40dB, gonna open up it up again later.

Doesnt matter if Comp or EQ are switched on or off, as soon as I press EQ>COMP the signal gets turned out by a large amount.

Which relays did you replace already? The EQ>COMP relays are K8 and K9 on the motherboard.

 

[punkt]

Which relays did you replace already? The EQ>COMP relays are K8 and K9 on the motherboard.

k1,2 k7,8,9 k 12

opened it up already

 

[TheseGoToEleven]

k1,2 k7,8,9 k 12

opened it up already

Ok so if K8 and K9 are brand new then they probably work fine. Start looking for resistance in the signal path. Measure resistance between:

- T12 and pin 2 of K8
- 64 and pin 2 of K8

 

[punkt]

Ok so if K8 and K9 are brand new then they probably work fine. Start looking for resistance in the signal path. Measure resistance between:

- T12 and pin 2 of K8
- 64 and pin 2 of K8

- T12 and pin 2 of K8 0 OHMS
64 and pin 2 of K8 0,6kOHMS measured likealways on the 200k OHMS setting^^

 

[TheseGoToEleven]

- T12 and pin 2 of K8 0 OHMS
64 and pin 2 of K8 0,6kOHMS measured likealways on the 200k OHMS setting^^

Ok those should have both been zero.

Now check these resistances to see what you can find. They are all supposed to be zero too.
T12 and pin 3 of K7
T12 and pin 8 of K8
T12 and pin 3 of K9
T12 and pin 8 of K12
64 and pin 9 of K9

 

[punkt]

Ok those should have both been zero.

Now check these resistances to see what you can find. They are all supposed to be zero too.
T12 and pin 3 of K7
T12 and pin 8 of K8
T12 and pin 3 of K9
T12 and pin 8 of K12
64 and pin 9 of K9

yup these all have zero resistance

 

[TheseGoToEleven]

yup these all have zero resistance

Ok all that is good. And finally the resistance between pins 2 & 3 of K7? That’s all that is left.

 

[punkt]

Ok all that is good. And finally the resistance between pins 2 & 3 of K7? That’s all that is left.

Also zero same goes for k8,k9,k12

 

[TheseGoToEleven]

Also zero same goes for k8,k9,k12

I forgot one. Only place left is between pins 8 & 9 of K9. Maybe measure between T12 and 64 again to make sure it still isn’t zero? You apparently got 600 ohms somewhere earlier, if the measurement was good.

With the unit unplugged, the signal path starting from the tube stage V2 output and ending at the Output knob goes in this order, and should have zero resistance between any of the steps:

Solder point T12
Pin 2 of K8
Pin 3 of K8
Pin 3 of K7
Pin 2 of K7
Pin 9 of K7
Pin 8 of K7
Pin 8 of K8
Pin 9 of K8
Pin 2 of K9
Pin 3 of K9
Pin 3 of K12
Pin 2 of K12
Pin 9 of K12
Pin 8 of K12
Pin 8 of K9
Pin 9 of K9
Solder point 64

 

[punkt]

I forgot one. Only place left is between pins 8 & 9 of K9. Maybe measure between T12 and 64 again to make sure it still isn’t zero? You apparently got 600 ohms somewhere earlier, if the measurement was good.

With the unit unplugged, the signal path starting from the tube stage V2 output and ending at the Output knob goes in this order, and should have zero resistance between any of the steps:

Solder point T12
Pin 2 of K8
Pin 3 of K8
Pin 3 of K7
Pin 2 of K7
Pin 9 of K7
Pin 8 of K7
Pin 8 of K8
Pin 9 of K8
Pin 2 of K9
Pin 3 of K9
Pin 3 of K12
Pin 2 of K12
Pin 9 of K12
Pin 8 of K12
Pin 8 of K9
Pin 9 of K9
Solder point 64

got a feeling its t12 again, put the multimeter on 200OHMS Setting and i get everywhere around 2,5 Ohms

took a video

just refsolderer 64 and t12, no changes

 

[TheseGoToEleven]

got a feeling its t12 again, put the multimeter on 200OHMS Setting and i get everywhere around 2,5 Ohms

took a video

Ok good video, thanks. Since your meter is set to 200 (not 200k) then the display shows ohms, not kilo ohms like before. Since it is only 2 or 3 ohms between T12 and 64, that isn’t going to affect the audio signal. You had 70k before reflowing T12, big difference. So these measurements are all good.

Maybe check the resistance from 64 to where the red wire connects on the tube board. That might tell you if the wire is bad.

If the unit is off, and the EQ>COMP is also in the off position, and then you turn the unit back on, does it work normally? And then stop working only after you press EQ>COMP?

 

[punkt]

Ok good video, thanks. Since your meter is set to 200 (not 200k) then the display shows ohms, not kilo ohms like before. Since it is only 2 or 3 ohms between T12 and 64, that isn’t going to affect the audio signal. You had 70k before reflowing T12, big difference. So these measurements are all good.

Maybe check the resistance from 64 to where the red wire connects on the tube board. That might tell you if the wire is bad.

If the unit is off, and the EQ>COMP is also in the off position, and then you turn the unit back on, does it work normally? And then stop working only after you press EQ>COMP?

it doesnt stop working, as soon as eq>comp is disengaged everything is fine, but as soon eq>comp, signal gets really quiet

cable is good, only 3ohms between 64 and the red wire

edit: video is uploading

 

[TheseGoToEleven]

it doesnt stop working, as soon as eq>comp is disengaged everything is fine, but as soon eq>comp, signal gets really quiet

cable is good, only 3ohms between 64 and the red wire

Ok got it.

With the EQ>COMP button turned on, measure the DC (not AC) voltage between pins 1 and 10 of K8, and between pins 1 and 10 of K9. Both should show 12 volts.

 

[punkt]

Ok got it.

With the EQ>COMP button turned on, measure the DC (not AC) voltage between pins 1 and 10 of K8, and between pins 1 and 10 of K9.

with the unit off, i get 0 everywhere ehh before measuring with the unit on, dont i bridge these 2 pins when i try to meassure them?
dont wanna do any harm

black cable in the com port and red cable in the v port, right?

 

[TheseGoToEleven]

with the unit off, i get 0 everywhere ehh before measuring with the unit on, dont i bridge these 2 pins when i try to meassure them?
dont wanna do any harm

black cable in the com port and red cable in the v port, right?

Yes, same set up as measuring resistance except the meter dial should point to the white “20V”. You can’t measure resistance when the unit is on but you can measure AC or DC, no problem. I want to see whether the K8 and K9 relays are receiving the proper control signal, which is 12 volts DC when the EQ>COMP button is turned on.

 

[punkt]

Yes, same set up as measuring resistance except the meter dial should point to the white “20V”. You can’t measure resistance when the unit is on but you can measure AC or DC, no problem. I want to see whether the K8 and K9 relays are receiving the proper control signal, which is 12 volts DC when the EQ>COMP button is turned on.

yup about 12v for k8 and k9 0 for k7 with eq>comp on

 

[TheseGoToEleven]

yup about 12v for k8 and k9 0 for k7 with eq>comp on

Ok so K8 and K9 are receiving the correct control signal. That’s good. K7 is fine; it won’t have 12 volts DC across pins 1 & 10 unless the “COMP” button is on.

Try turning EQ and COMP off, but turn EQ>COMP on. Send the sine wave into line in. Set the meter dial to 200V AC. Hold the black probe on any convenient grounded place, such as solder point 12, 15, or T7. Then with the red probe measure the AC at these points:

Solder point T12
K8 pin 2
K8 pin 3
K8 pin 4
K8 pin 7
K8 pin 8
K8 pin 9
All the same pins on K9
Solder point 64

Edit: measure on K8 & K9, not K7