caldog20

13V Zenner Diode - https://www.digikey.com/en/products/detail/diodes-incorporated/BZX84C13-7-F/775729 10V Zenner Diode - https://www.digikey.com/en/products/detail/good-ark-semiconductor/BZX84C10/18648842

When I get back home I can give you exact links from Digikey to order parts. As far as picture it really looks no different. Just unsoldered old diodes, cleaned pads, resoldered new diodes and done.

I just wanted to report back with my results. I replaced 13V Zenner Diode D3 and 10V Zenner Diode D7, and the problem has been resolved. The board is working properly now, reporting proper temperatures, and toggling the heater on/off at set temperature. Thanks, Caleb

Once my parts come in and I replace the diodes I will report back with my results in case anyone else has the same issue. No disrespect to the board repair people out there, but I prefer to fix these things myself if possible.

I had to put an LED flashlight under the board to actually see how hot it got. From looking at D3 and the colorization, it looks like it got hot. Also the trace between D7 and R32 is darker, same as mine, probably due to overcurrent in that area. You can see on your board D7 has taken some damage. I am replacing D7 and D3 on my board. I also checked the 2 resistors that were darkened but they both checkout out at 150 ohms which matches their code. This area must have something to do with the sensor circuit for readings/comparisons between the sensors for checking for flow. If you look on the back of the board in that area, you will probably see where D3 got really hot and made a square mark due to heat on the board. I have read this can be caused by a stuck heater relay, causing resistance in the temperature sensors to drastically reduce, which can cause overcurrent in the sensor circuit when the temperature stays too hot for too long. Might be a good idea to verify heater relays as well.

D3 is a burnt diode for sure. If it had markings on it I could identify it's voltage at least for replacement. Edit: Found markings after cleaning with ~pure Isoprop. D3 is a 13V Zenner Diode and D7 is a 10V Zenner Diode. I am going to go ahead and replace both. I will update if that fixes the problem.

I think I may have found the failure point. It looks like this area got extremely hot at some point. The resistors here look fried and possibly the 2 diodes.

One thing I did notice is that even though it consistently blinks OHH, if I short the sensor leads on it displays SnA or SnB depending on which one I short. I checked each sensor and they are reading proper resistance based on water temperature. So it seems the logic is working to some extent for the sensor readings.

I tested them and each tested okay. Are you talking about the black line on the heater relay? That is a shadow from the picture. From what I understand the heater relay being shorted won't immediately throw an OHH code immediately on bootup?

Hi, I have a Balboa EL2001 Mach 3 board that is immediately displaying an OHH flashing code. It has the same behavior whether topside is connected or disconnected. I have done some research and came to the conclusion it is more than likely a bad component on the board. I have done some testing and possibly found a bad diode but it has no markings for identification. I can't order replacements to repair without proper identification of the bad components. Does anyone have detailed schematics or information on these boards? The diode at D7 seems to be bad but it has either gotten too hot and the markings are gone, or just faded.