Smoked D3

[1991blazer]

So I have been running my system for about a year now but still having some VSS issues.

Took out the board and changed a capacitor on my VSS circuit and then hooked it up to my TranStim and D3 got real hot and started smoking. I checked my power supply and it was giving 16.8 volts at the time, been fine in the past but did not check it before using it this time. Got a different one that runs exactly at 12v but MS is dead. Any ideas on if the high voltage did that and what can I do to get it back up? This is the surface mount diode near the upper left corner.

Thanks.

[Bernard Fife]

1991blazer,

Anything near 17 Volts is a potential problem, so that would certainly be my first guess as to a culprit. The GPIO schematics are here: http://www.msgpio.com/manuals/gpiohw.htm. If this is a recent production board, then D3 is a 'safety valve' Zener diode on the power supply, and keep it from rising over 22 Volts (nominally +/- 10%) for brief spikes. Longer exposure to excessive voltage will fry this diode (but should protect components 'downstream'). D3 is the equivalent of the 22V D12 Zener diode on the V3 main board (http://www.megamanual.com/ms2/pcb.htm) or D3 on a microsquirt PCB.

I have never actually fried a D3 diode, but it certainly sounds likely that the input voltage took yours out. You can run a GPIO board without D3 but ONLY if you are absolutely sure the Vref voltage will ever climb above about 15 volts (I wouldn't be tempted to try this unless I had the board on a regulated power supply with a current limiting device on my bench).

Last time I checked, the production part for this item is Diodes Inc. number SMAZ22-13 (http://www.oemsec.com/product-detail/SM ... 43782.html). It's not terribly small for soldering with an iron and a light touch.

Lance.

[1991blazer]

That is what I thought. Replaced and seems to work fine. Thanks.

On a side note, looks like I got my VSS signal to even out on my 4L80E by adding a .04uf capacitor onto the signal coming in. Was having all kinds of problems and seems to have worked. Had a .07 uf on there and it fixed the low speed erratic behavior but started a very unstable speed at exactly 65 mph.

[Bernard Fife]

1991blazer,

I'm glad you are up and running again!

That's very good to know about the VSS signal. Thanks for sharing that. I will add it to the docs.

Lance.