MCS2000 PA Woes

[KE7JFF]

So I have a VHF MCS2000 Model 1; it was given to me from a friend who was clearing out a bunch of radio gear he no longer uses. I finally got around to program it up and of course I noticed its not putting out any significant RF Power; you can hear it on a nearby handheld of course, but not that far out. And this is both in the ham and public safety bands.

Whatever power it is throwing out, its not even registering on my crappy SWR/power meter. So I am thinking the PA has failed. I've haven't worked under the hood yet with a MCS2000 but even considering its a single board is there any hope in getting to TX full power again? It receives just great; I just don't want to trash it.

[fineshot1]

More info please.

There should be a label on the bottom.

Need "ID No" below Model No or at least tell us what power level(TX Wattage output)
and possibly the MFG Code or Flash Code(depending what the label says).

[KE7JFF]

Oh, oops sorry. Its a 25W unit. Flashcode is 000004-000000-6.

[fineshot1]

ok - make sure you did not make any errors in making your power measurement,
such as possibly a bad cable or like you said use a good quality power meter such
as a bird or telewave or equivelant.

If you still have no power out measured then your gonna have to take the head,
and cover, and shields off. Then with everything on the pcb exposed push the
head back on gently and hook up power and a dummy load and mic. Power up
the radio and turn to a simplex channel that you can key up on and not disturb
any users nearby. Using a millivolt meter during keyups your gonna have to
measure the millivolt output on the driver and final transistors on the rear
part of the pcb and determine if you driver or final transistors are bad. I am
not sure of the exact arrangement of driver & final transistors for vhf as we
only have uhf models but once you determine which one is bad then you will
have to get a replacement and they are not too hard to remove from the pcb
assembly.

Re-assembly requires you to tork down the torx screws in a certain sequence
via the numbered screws but I don't know the exact details without a manual
and don't forget to use a thermal compound on the transistor heatsinks before
torking down the screws to the main heatsink casing.

EDIT: I forgot to mention that it would be best to only snug and not tighten
the torx screws as they are only supposed to be torked to about 12 in lbs.

[KE7JFF]

Thanks!

I'll see what I can do with this thing; though surface mount components are kind of no fun lol.

[motorola_otaku]

Do the VHF units not use hybrid power blocks? I've only worked on 800 and 900 radios and their power blocks were super-easy to remove and replace.

[d119]

IIRC it's driver + final on the V/U units.

[fineshot1]

IIRC it's driver + final on the V/U units.

That is correct, the vhf & uhf MCS2000 radios use RF PA transistors and the 800/900
models use RF PA bricks.