Bosch HBLP451UC/03 wall oven

[BeaconWoods]

A few weeks ago we installed the above named oven in the kitchen of the house we are building.  We had purchased the entire suite of Bosch kitchen appliances but did not install them right away because building the house, running the farm, and holding down a full time job pushed off the install longer than expected.  Anyway, display lit up just fine for a few days then went out.  Having nearly 50 years in as an electronics tech (although not specializing in appliances) I tore into it.

I have learned a few things:

1. Electronic infant mortality remains a thing.

2. It is extremely hard to access Bosch tech manuals.

3. It is hard to tease out which component is bad without them.

The oven lights work as does the back light of the display.  The display itself goes black after a brief flash of white when the power is cycled.  I have found what I believe to be regulated 5 and 12 volts in the power supply section of the main control board (11020741).  Referenced to pin 1 of the three wire "cable" going from the x3 connector to the display board I find a little over 4 volts on pin 2.  It pulses downward every couple seconds.  I find 12 volts between pins one and three.  Same at the display board (8001210821) end of the cable, so the wires seem fine.  After the power has been on for maybe five minutes  or so, the semiconductor labelled IS501 becomes too hot to touch and the voltage between pins 1 and 2 drops to a steady 1 volt.  Neither of those conditions is affected by disconnecting the cable to the display board.  Given the above, I am fairly confident that the main controller board is the culprit.  I have checked the electrolytic capacitors in the area and they all seem fine as do the semiconductors.  I would love access to a copy of the schematics / tech reference.  I did manage to find a copy of the "Service Manual for Bosch Benchmark Series Built-in Wall Ovens" but it does not address the electronics in sufficient detail.

 

Thoughts?

Thanks,

Gary