Avalon vt-737sp

[a soBer Newt]

Q8 and Q7 Should be TIP48, these are pass elements for the 180V rail. I ran into the issue in production where the screw insulator would get damaged or the sil pad would get messed up and the back tab was then making contact with the heatsink and could cause havoc. U2 is a 350T and is for the 6.3V.

 

[Jdm5149]

K. Will check in a few days. When I tested supply pulled out of unit I would get 258v off of bridge rectifier near transformer. Then traced to Q8 and Q7 and would get similar voltage. The rectifiers are new. I have resoldered the heat sink because I felt it was compromised from taking supply in and out so many times. It is a tight squeeze. K.

 

[Jdm5149]

Will order new pads and screw insulators. Also.

 

[Jdm5149]

Replaced the sil pads on the Q7 and Q8 heatsink. Measured Q7 with 256v. Think I accidentally shorted it while reading. When I connected to motherboard ZD2 and R10 blew. Q1,3,4,7,8 damaged. U2 (350t) damaged also. The 12v and +-34 circuit still ok. Uggh. Anywhere I can just get a new power supply or board.

 

[Jdm5149]

Gotta order more parts. Does anyone know the voltages off the transformer. Each wire going to molex. Last week I did measure 256 coming off bridge rectifier

 

[pucho812]

Gotta order more parts. Does anyone know the voltages off the transformer. Each wire going to molex. Last week I did measure 256 coming off bridge rectifier

Why are you ordering a new power transformer?
Is something wrong with the one in there?
In all my bench time on those units, which would be upwards of thousands of units, the power transformer was replaced maybe once.
Those usually are fine.
Let me see if I have the color code for those to get proper measurements

 

[Jdm5149]

Yeah. Don’t think it’s the transformer. Just wanted to know the values. I replaced the molex connector in the beginning Pretty sure I got the two white wires on correct pin. I replaced all 4 bridge connectors. Pretty sure the 3 smaller rectifiers were same part number. I have to order the zen diodes 2/3. 2 was shorted after this last failure. Also w42 and 48 parts. Are these how these 2 parts are connected to board ?

 

[Jdm5149]

K update. New parts arrived and now I have the original condition. Have 183v. 12v. +-34. But the 6v is sliding down. When I test 350t with supply out of the unit. One side reads 530 and other 235. It’s a new 350t. Even when not placed in board the pins read the same. Any ideas.

 

[Jdm5149]

T1 - 183v
T2 - 2.9v
T3 - .049v
T4 - 35v
+-34 tests good at all points.

 

[Jdm5149]

I also notice that c23 is 3300uf 24v. Isn’t it suppose to be 4700uf 16v. That is how I got the unit so I just replaced with the 24v. Ordered a 4700/16 so …..

 

[pucho812]

Very nice.
So far so good although it looks like your 6v is having an issue again.
Che on your kbu6d and c23.
Replace as necessary.
I forget the c23 value off hand.

 

[Jdm5149]

Yeah. I saw one of your old post and it was 4700/16. The c23 I originally replaced was 3300/24. It looked like it had been replaced at least once. Also I don’t know if it matters but r12 is missing. Is that also normal.

 

[Jdm5149]

R12

 

[melmsmidth]

I had problems with the 6V in the past too, be sure to solder the kbu6d properly and check the tracks on the 4 pins. In my case the problem was one of the tracks from the diode bridge was damaged so check continuity between components to be sure that the voltage is reaching the next pad.

 

[Jdm5149]

Hi there. I spoke to u on another thread. I replaced the rectifier and molex connection. It did seem to work when I did that but while testing I damaged the 180v somehow. So now it’s back to the original state in which I got it. I will continue. lol!

 

[melmsmidth]

Hi there. I spoke to u on another thread. I replaced the rectifier and molex connection. It did seem to work when I did that but while testing I damaged the 180v somehow. So now it’s back to the original state in which I got it. I will continue. lol!

Sorry I missed your post! (Or not, I’m a little distracted lately) Hope you find the fault but once again check track continuity. I had a lot of head schatching because of that!

 

[pucho812]

R12

How is R11? It looks to toasted.
R12, on drawings I have it’s listed as a 15k resistor but there seems to be some debate there as originally it was listed as a value of rx and then someone updated it with 15k

 

[Jdm5149]

Yes. That was an old pic. Already replaced. So r12 should have a resistor there ? There was never one there.

 

[pucho812]

Yes. That was an old pic. Already replaced. So r12 should have a resistor there ? There was never one there.

It might be dni, do not install. If your unit came without it and was working, don’t put it in. Hard to keep track of revisions.

 

[Jdm5149]

Agree. 4700/16 arriving today. But I think it’s something else in that circuit. K. I’ll let u know