MJE5731A voltage different

[Paul Birkeland]

I would pop a fresh 2N2222 in on the offending side. 

[tintin]

Thanks Paul part is on order- unfortunately I think I may have created another problem while testing; I accidentally shorted the blue wire from terminal 21 to the tab on terminal 28, there was a small spark and now the corresponding MJE5731A reads 170V. Is it possible I have damaged the transistor, or another component? Will wait for your guidance on any further tests and if I should order another part too. Thanks

[Paul Birkeland]

There is no blue wire that goes to terminal 21, do you mean the blue wire on 28 touched something it shouldn't?

I would advise disconnecting the blue wire that leaves that half of the shunt regulator and report the OB and KregB voltages.

[tintin]

Apologies, yes the blue wire from terminal 28 touched terminal 21.

With the blue wire disconnected, OB = 175V, KregB = 0.11V. OA= 220V and KregA=1.9V within range I believe.

[Paul Birkeland]

The 431 regulator on that side appears to be blown.

[tintin]

Thank you for the speedy diagnosis, will order another 431 regulator as well and work from there. Is there reasonable suspicion for any other parts to be ordered in case they may have been affected too? Just trying to save on shipping costs in case.

[tintin]

Just to confirm, will any of these be suitable? The only difference I can see in specs is the operating temperature.

https://www.digikey.com.au/en/products/detail/texas-instruments/LM431AIZ-LFT1/3901932
https://www.digikey.com.au/en/products/detail/texas-instruments/LM431BCZ-NOPB/364136
https://www.digikey.com.au/en/products/detail/texas-instruments/LM431CIZ-NOPB/364143

Thanks again

[Paul Birkeland]

https://www.digikey.com.au/en/products/detail/onsemi/LM431ACZ/1049094

[tintin]

Got it, will update with results when parts arrive. Thanks again for the ongoing support, much appreciated

[tintin]

I have put in a fresh 2N2222A and still have incorrect readings

With the blue wire disconnected, MJE5731A reads 220V correctly, with it connected, it reads 150V. Further:

IB= 150V
OB= 150V
OD= 145V
OkB= 145V
OkD= 0V

I am sure the 2N2222A was installed correctly, as the legs are 0 resistance to other components connected via the PCB.

Am waiting on the LM431 part which should resolve the shunt board, but that is a problem in the other channel.

[Paul Birkeland]

The 0V at 0KD would still make the 2N2222 suspect.  I believe we have also seen similar issues to yours when a trace on that PC board up front has been damaged.