Re: MJE5731A voltage different

zachely · **on:** October 08, 2024, 02:56:42 PM

I believe I’m having a similar issue. My Eros was working great and previously passed all voltage tests. After moving the Eros inside and listening to music, I heard a loud pop, which I believe blew the LM431 regulator. I ordered replacement parts and cleaned up some solder points. Now, the B side of the Shunt Regulator reads 220 VDC and the A side reads 263 VDC. Any other parts I should consider replacing? Potentially the MJE5731A transistor?

Paul Birkeland · **Reply #1 on:** October 08, 2024, 05:57:58 PM

What are your Kreg voltages on the regulator board? How did you come to the conclusion that the 431 was blown?

zachely · **Reply #2 on:** October 09, 2024, 02:38:16 PM

Kreg A reads 3.8 VDC. Kreg B reads 6.4 VDC.

Paul Birkeland · **Reply #3 on:** October 09, 2024, 02:54:40 PM

That is enough Kreg voltage for the 431 regulators to draw down and regulate. I would recommend using the continuity setting on your meter to check for shorted transistors on the C4S board above the D socket.

Additionally, these circuits don't generally go pop on their own, so you can continue replacing parts on something like this and it's completely likely that the problem will continue to present itself. What I would be looking for would be adjacent terminals on the D 9 pin socket being shorted together by improperly routed components or debris in the area. The same would go for the C4S board mounted to that socket, as shorts on that board can cause similar problems.

zachely · **Reply #4 on:** October 10, 2024, 03:42:05 PM

Well, I’m feeling a bit defeated. I confirmed that none of the terminals on the D 9-pin socket are touching one another. I’ve resoldered and checked everything on the board above the D socket with no luck. The board is starting to lose its integrity as I’ve soldered and desoldered numerous times.

Is it safe to assume that the problem lies within the D 9-pin socket and the accompanying board above? Should I investigate any other areas?

Paul Birkeland · **Reply #5 on:** October 10, 2024, 06:12:06 PM

I'd imagine there's a shorted transistor on there, either the MJE5731A or PN2907. You can set your meter to beep for continuity and check each pair of leads on each transistor to see if any of them show a dead short.

zachely · **Reply #6 on:** October 11, 2024, 03:24:08 PM

I appreciate your help. The transistors appeared to be in good shape. Although, the board has seen better days so I’m going to rebuild. I’ll report back in a couple of weeks.

Paul Birkeland · **Reply #7 on:** October 12, 2024, 09:20:02 AM

Did you do the shorts test between pairs of leads?