CDM1250 PA problem

[Martel]

Hi...

I have a LDMOS 45 watt CDM1250 VHF mobile with a weird PA problem.

The problem resides with the driver LDMOSFET (MRF1518T1) blowing.

I have a channel set at 138 MHz 30 watts and a 168 MHz channel set at 20 watts. When i transmit at 138 MHz, i have a mere 7 watts but the driver works. When i switch to the 167 MHz, no power at all, then i switch back to 138 MHz and no power at all. When i check the MRF1518, it is blown (Gate short-citcuited to Source).

The MOSBIAS 1 is at 2.2 volts and MOSBIAS 2 is at 2 volts. The final (MRF1550) tests okay.

Anyone has got that king of trouble ?

Normand

[d119]

I've never met a series of radio with a more finnicky PA than the CDM series.

My recommendation is a trip to the depot.

[35echo]

Martel,

TP3502 VCNTRL 3.40Vdc tx 0Vdc rx
TP3503 PCIC pin 1 3.61Vdc tx .74 Vdc rx
TP3504 K9V1 9.0Vdc tx 0Vdc rx
TP3506 Mobias2 2.26Vdc tx 0Vdc rx
TP3508 Mobias1 2.53Vdc tx 0Vdc rx
TP3509 Vsense 3.41Vdc tx 0Vdc rx

These readings are from a CDM1250 45W LDMOS IMUD6015B Board with a T12 controller and a P3 PA version
13Vdc supply / 46watts out of radio
Also just because the final doesnt read a short from source to gate or source to drain doesnt mean it is good.
I have seen them vary tx out according to where they are in the range of the radio. I have also seen them kill the driver before.

Regards,

Allen