Diodes without a cap cant be good for the other semiconductors.

When removed the big cap and measured around under power nothing popped however could I have damaged something else? I saw no signs of anything going wrong tho.

 

I am looking for LM393, however I see almost all of them have an additional digit at the end "LM393P" Are those just revisions is it still just a LM393?

 

Tantalum caps are notorious to short and/or catch fire easily.

I will check them.

 

LM393-X is a Low Power Low Offset Voltage Dual Comparators which is a bit unusual and why I asked as to the schematic to see just what is going on with this PCB. Ignore the -X as it is usually an updated model and typically not an issue. Yes, diodes are current limited devices and increasing their current capacity with a higher rated diode would/could cause problems downstream without having the schematic to analyze. Contact the mfg and see if a schematic is available. How long did this board operate before giving problems? As to the XFMR being soldered onto the board, I wouldn't remove it but trace down to the next component, remove at that point to test. Do you have a Variac available to test with using lower input voltages to the XFMR? Start @ ~30VAC input to the XFMR and check polarities as you go. If everything OK @ 30VAC then keep bumping up the voltage until you reach the rated 120VAC and if no problems, go to the next stage @ 30VAC and repeat the procedure. You need to find out just how the LM393 is being used. That is something not familiar to me.

 

They are all LM393 but there may be some subtil differences look at the datasheets.

I did look in the datasheets for what I could put together there are new revisions with newer whatever they add but I was unsure if they all were LM393 interchangable. For what I can see they are.

 

LM393-X is a Low Power Low Offset Voltage Dual Comparators which is a bit unusual and why I asked as to the schematic to see just what is going on with this PCB. Ignore the -X as it is usually an updated model and typically not an issue. Yes, diodes are current limited devices and increasing their current capacity with a higher rated diode would/could cause problems downstream without having the schematic to analyze. Contact the mfg and see if a schematic is available. How long did this board operate before giving problems? As to the XFMR being soldered onto the board, I wouldn't remove it but trace down to the next component, remove at that point to test. Do you have a Variac available to test with using lower input voltages to the XFMR? Start @ ~30VAC input to the XFMR and check polarities as you go. If everything OK @ 30VAC then keep bumping up the voltage until you reach the rated 120VAC and if no problems, go to the next stage @ 30VAC and repeat the procedure. You need to find out just how the LM393 is being used. That is something not familiar to me.

Thank you very much Sam, I'll reach out to Fadal that is the maker of the card with that said I am unsure if they will help since this card is very old 20+ years. I do not have a Variac unfortunately but everything you say makes sense I am going to have to get creative

 

Probably is, your circuit looks simple enough.

I put my order in

 

Hi gents, I finally received the LM393, and to my disappointment the board does the same after I swapped it
I think there is not much left to change, I doubt it is the resistors so if I am correct it is down to the tantalum caps or the transformer.
I have 2 tantalum caps a +K 10u 35 and +A 047 35, I am thinking that is a 10uf 35v and a 0.47uf 35v am I correct? Could you folks please confirm?
Also the 0.47uf 35v is turning to be difficult to find, could I use a 10uf 35v in its place?
Anyhow folks I do appreciate your input and guidance, I am hoping it is the tantalum caps. Thank you!

 

I removed the tantalum cap from the board and power it and still the same diode starts to overheat without the cap, could it be that the tantalum cap is regulating the power to the diodes? I know it might be a really dumb question, apologies in advance.

 

And I almost forgot to post the back of the board.

 

You are powering the PCB with nothing else attached, right?

That is correct Anniel, I will find a local shop to take it. Thank you!

 

Anyone can recommend a shop in Las Vegas Nevada? I did a search for electronics repair it seems all I can find is computer and cellphone repair, I called a few places no one that could take a peek at my board