MCS2000 Reversed Polarity

[Param-A-Dic]

K, so a friend of mine recently dumped a good chunk of change on a model 2, vhf, 110watt MCS2000 only to have some shmuck do the install job for him and wire the power backwards...yeah, red to black and black to red...who knows.
i'm not too familiar with these, i'ved used 'em and programmed 'em, but never worked on and or repaired them.
so the first thing i found is part number 1705876X01 (MOL calls it a resistor shunt) looked as if it got real hot...practically seperated it from the board. so i reseated/soldered that.
the PA/power management board now seems to pass power to the 12 pin connector that interfaces to the main logic board. (good continuity, 12vdc present on pin one, if counting left to right with power/antenna connectors facing you). Radio is still a no go. won't power on.
so is there a fuse and/or diode around somewhere that i'm missing? is this thing fried...is it a job for the extremely over-priced Depot? should i tell him to dump $600 on a new logic board?
any thoughts
thanks
-jonathan

[jackhackett]

Depot it and make the installer pay, they have insurance, right?

There is a protection diode, underneath the PA board held in with a spring I believe.. I'm guessing they also didn't use any fuse and that diode blew open, which allowed the damage to go further.

I'm not positive what that resistor shunt you mentioned is without checking, but if it's what I think, it's the PA current measuring shunt, if that overheated the PA transistors are likely to be toast also.

Sounds like this one falls under the category of "You can pay us now, or you can pay us later"

[wa2zdy]

If there had been a fuse in there as Jack mentioned, it would have blown before any damage had resulted. The protection diode, like any diode, conducts only when the anode is positive. It's installed so the anode is on the negative power lead. So it only conducts if the supply is connected backwards, as apparently happened in this case. When connected backwards, the diode is like a short and pops the fuse. Of course if there's no fuse, the diode merely nukes itself and reverse polarity current continues to flow, taking the radio with it.

Yep, time for the installer to make file a claim against his insurance carrier. If he isn't insured . . . an expensive lesson for either him or your friend. Then the installer needs a pair of glasses to help him tell black from red. It's not that tough.