Avalon VT 737 sp

[TheseGoToEleven]

Good morning my friends, yea just tried to desolder them, no luck tho, i ordered a cheap desoldergun for bout 30€ in hope this will do the job https://www.amazon.de/dp/B09GV5B1SR?psc=1&smid=A2ROFELMX9359Y&ref_=chk_typ_imgToDp

This should help a lot compared to using separate heat and suction tools.

 

[punkt]

Sometimes it is tricky to get a good connection with the tip of the probe, so that you can get an accurate measurement. Since your measurements are inconsistent, I suggest taking each measurement more than once, until you are confident about the result. And for resistance you can switch the order of the probes too. Like measure first with the red probe on 2 and black on 3, then with black on 3 and red on 2. Make sure they agree.

Expensive probes have this difficulty too, especially if the surface you are measuring is not pristine. I just hope the measurements are accurate because it’s all we have to make the diagnosis.

What to check next incase k7 turns out to be fine, because i get 0 resistance meassuring right at the legs of the relay

k12 is fine, i measured the wrong pins yesterday

yup k7 seems to be also fine

i suspect something is wrong with k9, because on all the other relays i got readings of 0 while k9 doesnt get any readings on 2&3 and 8&9

while all other relays get a measurment of 180 on 3&4, k9 gets 0

 

[pucho812]

just tested again, nope no readings on 63 or 64 whatsoever even when cranking up gain and output and t12 readin 13, no readings on 63&64

just saw that on the tube card c5 and c4 are flipped upside down, never touched these ones, is this normal?

C5 and c4 are not polarized capacitors so yeah that’s ok as far as orientation

 

[TheseGoToEleven]

i suspect something is wrong with k9, because on all the other relays i got readings of 0 while k9 doesnt get any readings on 2&3 and 8&9

while all other relays get a measurment of 180 on 3&4, k9 gets 0

Pins 3 & 4 on K9 will be shorted (zero resistance) when the relay is "on". So it looks like K9 is stuck in the "on" position even though the unit is unplugged. So K9 should be replaced.

K8 and K9 are supposed to always match. Both on or both off. When the unit is plugged in, they receive the same control signal, which comes from the "EQ->Comp" button.

For an experiment you could try operating the unit with the "EQ->Comp" button turned on, and see what happens. If only K9 is bad, your signal might come back.

 

[punkt]

Pins 3 & 4 on K9 will be shorted (zero resistance) when the relay is "on". So it looks like K9 is stuck in the "on" position even though the unit is unplugged. So K9 should be replaced.

K8 and K9 are supposed to always match. Both on or both off. When the unit is plugged in, they receive the same control signal, which comes from the "EQ->Comp" button.

For an experiment you could try operating the unit with the "EQ->Comp" button turned on, and see what happens. If only K9 is bad, your signal might come back.

what would be the next stage to check after die relays are ok and it still doesnt work?

nope no changes

k7 has 0 ohms between 3&4 is that correct?

as k7 is the relay for the compressor i dont think this is right, seems that it also on the on position, turning on every knob doesnt help really only boosting the eq really does an impact on the test sinewave

 

[TheseGoToEleven]

k7 has 0 ohms between 3&4 is that correct?

as k7 is the relay for the compressor i dont think this is right, seems that it also on the on position, turning on every knob doesnt help really only boosting the eq really does an impact on the test sinewave

With the unit unplugged, pins 3 and 4 should be disconnected from each other (infinite resistance) on all relays. If the resistance is zero then it is stuck in the "on" position and needs to be replaced. Pins 2 and 3 should be shorted together (zero resistance). Also just in case... never measure resistance with the unit turned on.

 

[punkt]

With the unit unplugged, pins 3 and 4 should be disconnected from each other (infinite resistance) on all relays. If the resistance is zero then it is stuck in the "on" position and needs to be replaced. Pins 2 and 3 should be shorted together (zero resistance). Also just in case... never measure resistance with the unit turned on.

i messed up a bit, any tipps on how to desolder the bridged pins, no matter what i do i cant get it off

 

[TheseGoToEleven]

i messed up a bit, any tipps on how to desolder the bridged pins, no matter what i do i cant get it off

That’s K2 on the tube board, so it is ok. There is a trace on the PCB that keeps those two pins shorted on purpose. The solder is attracted to that trace, which makes it hard to remove. But you can leave it like this.

 

[punkt]

That’s K2 on the tube board, so it is ok. There is a trace on the PCB that keeps those two pins shorted on purpose. The solder is attracted to that trace, which makes it hard to remove. But you can leave it like this.

replaced all the faulty relays, no changes

k2 and k8 still have infinte resistance between 3&4
k7 has 180 ohms between 3&4 even tho i just replaced it

 

[TheseGoToEleven]

replaced all the faulty relays, no changes

Ok so with the unit off, can you measure the resistance between T12 and 64 again?

 

[punkt]

Ok so with the unit off, can you measure the resistance between T12 and 64 again?

69,5

 

[TheseGoToEleven]

69,5

When the unit is turned off, T12 and 64 should be shorted. Did you replace K7, K8, K9, and K12?

 

[punkt]

When the unit is turned off, T12 and 64 should be shorted. Did you replace K7, K8, K9, and K12?

not k12 but k1 and k2, will replace k12 now

 

[TheseGoToEleven]

not k12 but k1 and k2, will replace k12 now

Well you can check the pins on K7, K8, K9 and K12 for resistance first if you like. One of them must not be working properly. Also the K2 that controls phase is on the motherboard (under IO card 7372), not the tube card. Not sure whether you replaced that one yet but it can wait since it’s not part of the problem right now.

 

[TheseGoToEleven]

A little re

replaced all the faulty relays, no changes

k2 and k8 still have infinte resistance between 3&4
k7 has 180 ohms between 3&4 even tho i just replaced it

With the unit off, test to make sure that 2 & 3 are shorted on K7, K8, K9, and K12. And that 8 & 9 are also shorted on K7, K8, K9, and K12. Don't worry about other pins until you find one where 2 & 3 or 8 & 9 are not shorted.

 

[punkt]

Well you can check the pins on K7, K8, K9 and K12 for resistance first if you like. One of them must not be working properly. Also the K2 that controls phase is on the motherboard (under IO card 7372), not the tube card. Not sure whether you replaced that one yet but it can wait since it’s not part of the problem right now.

all relays show now 0 resistance between 2&3 8&9

resistance between t12 and 64 still persists

 

[TheseGoToEleven]

k10& k11 are faulty ig 2&3 resstiance is 0,

edit: all relays show now 0 resistance between 2&3 8&9

Ok one last time to be super clear: When the unit is off, all relays should have zero resistance (shorted) between pins 2 & 3 and between pins 8 & 9.

So if they all show zero resistance in those places then that is good, and there should also be zero resistance between T12 and 64.

Also, K10 and K11 have nothing to do with your current problem so I wouldn't worry about them for now.

 

[punkt]

Ok one last time to be super clear: When the unit is off, all relays should have zero resistance (shorted) between pins 2 & 3 and between pins 8 & 9.

So if they all show zero resistance in those places then that is good, and there should also be zero resistance between T12 and 64.

Also, K10 and K11 have nothing to do with your current problem so I wouldn't worry about them for now.

my bad, all relays are good now, but the resistance between t12 and 64 is still at 71,5

 

[TheseGoToEleven]

my bad, all relays are good now, but the resistance between t12 and 64 is still at 71,5

Ok let's dig a little deeper. What is the resistance between:

T12 and pin 2 of K8
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

Remember when looking from the bottom, the square solder pad is pin 1 and then they are numbered clockwise like this:

 

[punkt]

Ok let's dig a little deeper. What is the resistance between:

T12 and pin 2 of K8
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

Remember when looking from the bottom, the square solder pad is pin 1 and then they are numbered clockwise like this:
View attachment 147381

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