Avalon vt-737sp

[chrispbass]

Test with power transformer not connected in circuit.
Test with PSU not connected. In circuit but connected to power transformer.

Check rectifiers.

Thanks Pucho…appreciated. The unit has been lent out to a friend of my friend, so I need to get it in the bench to take a proper look. Would it be ok to PM you if needs be?

 

[pucho812]

Thanks Pucho…appreciated. The unit has been lent out to a friend of my friend, so I need to get it in the bench to take a proper look. Would it be ok to PM you if needs be?

Sure

 

[chrispbass]

Sure

Thank you. When I mentioned I was interested, it was the possibility of a common fault which I suppose would only be noticed by someone familiar with time served repair/product familiarity of these. Not the case for me, but competent enough to sort it and an experienced helping hand would be perfect. Thank you

 

[pucho812]

Thank you. When I mentioned I was interested, it was the possibility of a common fault which I suppose would only be noticed by someone familiar with time served repair/product familiarity of these. Not the case for me, but competent enough to sort it and an experienced helping hand would be perfect. Thank you

Well the best way to trouble shoot that is with a variac and monitor current draw. When on a variac from 0vac to mains, current will increase but eventually level off in a working unit. But in a faulty unit current keeps increasing until the fuse pops. The variac gives you a few seconds to probe before the fuse pops. In that time you can feel the rectifiers and see which one is too hot to touch and that’s your faulty one.

 

[chrispbass]

Well the best way to trouble shoot that is with a variac and monitor current draw. When I’m a variac from 0vac to mains, current will increase but eventually level off in a working unit. But in a faulty unit current keeps increasing until the fuse pops. But the variac gives you a few seconds to probe before the fuse pops. In that time you can feel the rectifiers and see which one is too hot to touch and that’s your faulty one.

I’ll be getting it here in a couple of weeks, so will be interesting to see if there is indeed a typical fault on these. Cheers

 

[Jdm5149]

Hi again. Replaced that resistor and still no luck. Are all the diodes on board same value. I replaced all with same value. Can D2 and D3 be different.

 

[pucho812]

Hi again. Replaced that resistor and still no luck. Are all the diodes on board same value. I replaced all with same value. Can D2 and D3 be different.

Yes highly possible. As I don't have a power supply schematic I don't have those values off hand. As you did talk with Greg at audio rehab, I would ask him about that. As an authorized service center he would have those.

 

[Jdm5149]

Haha. Greg is tired of me I think. He wants me to ship but I’m really into tinkering and learning how to fix things. I’ve built a few hairball 1176’s. A LA2A that is so great. A SSL clone. On this one I would go to local elec store and I just brought in one diode. He gave me like 20 of same value and I replaced all onboard with those. Since I’m a newbie I didn’t realize there are diff values. I picked up an assorted pack today. Now I think that’s when the 180 disappeared. K. Guess I’ll do Alittle more research. Thanks for all your help !!

 

[Jdm5149]

R10 is 100R it should connect between B of Q4 and C of Q3

Hi. Would u know the values of D2 and D3 Or part number

 

[a soBer Newt]

Hi. Would u know the values of D2 and D3 Or part number

ZD2/3 Are 51V 1W D2/3 Are 1N4004

 

[Jdm5149]

ZD2/3 Are 51V 1W D2/3 Are 1N4004

Great. Like I said I replaced all diodes with exact value without knowing. Newbie. I’m hoping that is why the 180v is now 77. Gonna swap out Monday. Thanks a lot for the info.

 

[Jdm5149]

I noticed someone stated 1n4004 in an old post and I was gonna put them in. Now I know for sure

 

[pucho812]

Great. Like I said I replaced all diodes with exact value without knowing. Newbie. I’m hoping that is why the 180v is now 77. Gonna swap out Monday. Thanks a lot for the info.

Shotgunning parts will not get you any closer to being solved.

Isolate the psu

 

[Jdm5149]

ZD2/3 Are 51V 1W D2/3 Are 1N4004

Shotgunning parts will not get you any closer to being solved.

Isolate the psu

Isolate?? Take out and put on bench or test separated from main board. That’s what I’ve been doing. Unplugged from main board. Testing at end of molex. Im just assuming because I’m thinking that when the 180v went down to 77. I didn’t change ZD2/3. Only the regular diodes. Newbie so I didn’t check if they were different values.

 

[Jdm5149]

I’ll be installing the 1n4004 Monday morning. I’ll let the group know.

 

[Jdm5149]

K. Still no good. All the diodes I installed were 4007. Does anybody know each diode value and would it make a difference since 4007 is 1000v. Newbie question. I still get my 12v. +-34v at every point in unit where pucho812 stated. 6v now is around 5. B+ is 77.

 

[Jdm5149]

Also part U2. My original read 350T QAN351. Is that a specific regulator. Thanks for any help

 

[a soBer Newt]

What voltages do you have at pin 2 of Q8 and Q7 TIP48?

 

[pucho812]

K. Still no good. All the diodes I installed were 4007. Does anybody know each diode value and would it make a difference since 4007 is 1000v. Newbie question. I still get my 12v. +-34v at every point in unit where pucho812 stated. 6v now is around 5. B+ is 77.

|4004 vs 4007 is negligible can use either or IIRC

What voltages do you have at pin 2 of Q8 and Q7 TIP48?

Excellent question. I wish I had copy of the PSU schema but alas, no schematics here.

 

[Jdm5149]

K. I’m burnt like a f’ing transistor. lol will try again on Wednesday. It’s so frustrating. Like I said. I got the unit missing the 6.3 volts. Had everything else. I fix the 6.3 and the 34’s had problem. Now all good except for the B+. Thanks everyone for all your help so far. I will try again on Wednesday. The 350t I’ve been putting in have t12 on it. I see others that have t220.