MT2000 Mdl III VHF No Tx Power

[Vercomm]

Hi Guys,

I'm playing with an VHF MT2000 that has no Tx power out of the antenna port. Nothing shows up on service monitor, so Itried a couple other radios to make sure my equipment was okay and it checks out. The receiver on this problem MT2000 works great.

So moving forward into the MT, I checked U105 and all voltages look okay when radio is keyed. I checked all the way up to the backside of CR108 and the DC voltage looks good. I checked the DC voltage coming out of the antenna switch and it seems a bit low as compared to a VHF HT1000. but I don't see what the value should be in my service manual.

Any body else had this kind of an issue with the Jedi, is there a componenet that is usually to blame. Any pointers would be much appreciated!!

Thanks,


Jamie T

[d119]

Did you check the RF level coming off of the side RF adapter port that's used for remote speaker microphones & converacoms? It's possible the RF plunger switch that's engaged by the accessory has gone bad, and is stuck in the "external" position. Try pushing the plunger with a small, flat object in and out a few times to see if you get any resolution.

Granted, this would also affect receive, but it's worth a shot anyhow. The RF PA may be to blame as well, I've seen enough of those go out.

[Vercomm]

The testing I did was without the fron tcover on so the antenna switch was not activated unless there is a physical problem with it. I checked the PA with the values in the manual and they seem to be okay, I even checked them againt an HT1000 and they looked ok.

Any other thoughts?

[d119]

Bad diode somewhere...

[Vercomm]

The voltages are good at CR108 & CR109, which are the two diodes befoe the antenna switch. The both have correct voltages in Tx and Rx. Any other thoughts before I send it away for flat rate repair.

[N9LLO]

Bad PA. The only way to know for sure is with an RF probe.
Do you pick anything up on a nearby scanner set to the TX freq? This will tell you if your VCO is working.

Chris
N9LLO

[Vercomm]

I just checked the radio and yes, it will actually unsquelch another radios receiver if very close. I tested even further and found out you can actually get about half a block away and it still works, but any further and nothing.

What part number do you guys have for the VHF PA. I have it as: U501 - 5105385y36

How would I check the PA with an RF probe? All i have is a service monitor with a built in oscilliscope and probe. Is that what I require? What am I looking for around the PA?

Thanks

Jamie