Hello guys I repairing my HP3632a power supply and need to find a replacement thyristor for CR28 on the schematic, it's a MCR264-4 , closest I can find on Digikey is a S4040RQ3TP .. I am quite new to the electronics hobby and have done quite well finding replacement transistors but some are a little more challenging and I could really use some help with this .. The problem I'm finding is knowing how far I can deviate from spec on a transistor ..
That looks like a good substitute. The SCR is for over-voltage protection and normally does not turn on until there is a fault in the power supply that causes excess output voltage. If the SCR is shorted it is clear that it needs to be replaced. Determining what caused that failure is important so you don't get continuing over-voltage faults. What fault exists in the SCR?
Thanks Bill .I am going through it now checking to make sure all the components that were replaced prior to me purchasing it meet or exceed specs , I had no Idea that CR28 was missing when I purchased so I have no Idea what was wrong with it prior to my purchase . The supply seemed to be working fine when I purchased it . In hindsight I guess I should have checked it over when I got it , One day I smelt the magic smoke and it dropped to 1/2 power . It would read the correct voltage but would only output exactly 1/2 of the set voltage . When I inspected it rectifier CR3 was burnt out and lifted from the board explaining the voltage drop.. I found the caps in the path of CR3 are down 30% and are only reading 60 on the phase angle so will replace those too.. I will install some parts and power it up slowly while watching the current draw to make sure it does not have another short .. thanks so much on the verification of my part choice .. cheers Roger