diode damage from inrush current?

[donovas]

im using psu board with dinky 1n4004 diodes in them, double bridge mode. and the tranformer is 200vac EI.

I have two setups like this and only difference is that on setup A the transformer is not varnished, (i meant to do it myself later) and has only one secondary tap of 0,27v, where as setup B has varnished tranformer and secondary taps of 0,9,12,27v.

on setup A, the 1n4004 diodes on the PSU spark and blow whenever i turn on the amp.

setup B runs fine, even when i transfer the PSU from the setup A. so i'm sure the difference of the transformers is causing the issue. board from setup B does the same thing in setup A

What is the issue?
and why is it happening?

thanks in advance.

 

[codewritinfool]

By unvarnished, do you mean that there is no insulation whatsoever?

 

[donovas]

No, no insulation.

Its an Ei transformer

 

[codewritinfool]

Maybe I'm misunderstanding something, but transformers don't work without insulation on the windings.

 

[donovas]

Theyre insulated, just not dipped in varnish

 

[KMossman]

photos?

 

[Pafi]

Is there any capacitors, load, or nothing but the diodes and trafos?

 

[Pafi]

Did you measure secondary voltage and resistance?

Is PSU connected to safety earth in any way?

There are many possibilities...

 

[Pafi]

27V 1A=>27 W. With 200 VA trafo. Something is missing.

 

[Mooly]

I guess the wording in post #1 is open to interpretation but this reads like 'Amp A has fault that is blowing the PSU'.

PSU A and PSU B boards are proved OK in amplifier B. Q.E.D. amplifier B obviously works.

PSU A and PSU B boards self destruct powering amplifier A. What about amplifier A ? Has that been proved good.

 

[cbdb]

Are both transformers 200va?
A 1 amp diode looks too small for that 200va tranny. Try a 3 amp. The first cap charging pulse pulls full short circuit current. Measure these from the transformer to see the difference.

 

[Sorento]

on setup A, the 1n4004 diodes on the PSU spark and blow whenever i turn on the amp ...

where exactly is the power switch located ?
- in front of trafo between mains and trafo
- between trafo and rectifier
- between rectifier and reservoir cap
- between caps and amp ... ?

double bridge mode is what ? ... 4 diode Graetz ... ?

how many microfarads behind bridge ? maybe 0.x ohm requ'd if 1000's of uF

any connectors involved - maybe different between setups or wire gauge different ?

 

[Pafi]

I guess the wording in post #1 is open to interpretation but this reads like 'Amp A has fault that is blowing the PSU'.

PSU A and PSU B boards are proved OK in amplifier B. Q.E.D. amplifier B obviously works.

PSU A and PSU B boards self destruct powering amplifier A. What about amplifier A ? Has that been proved good.

Is there any amplifier? I see nothing referring to them.

 

[Mooly]

Post #1

the 1n4004 diodes on the PSU spark and blow whenever i turn on the amp.