Mark V

RX&Audio

Problems

Receiver Won't Receive

Problem: My MarkV would not receive. I got back into town last night after a week away from home on business and continued digging into my MkV to troubleshoot the lack of RX.

Solution:  As said last week, there is a T/R circuit at the antenna input to the rig that employs three transistors, a pin diode switch, and a relay. The relay wasn't being activated. I was able to make the relay work by supplying 12V to it and the rig received fine. Today I did some troubleshooting and found that Q6451 was bad. I replaced it, and while I was at it, I also replaced Q6450. I verified correct operation of the circuit and the rig works FB now.

Troubleshooting the problem and replacing the transistors was relatively straight forward. Digging into the rig and getting the main antenna tuner board out was pretty tricky. If you have any questions, don't hesitate to ask.

Lou W7HV
 

Deaf Receiver (Mark V)

Problem: "During contests, anything can happen. For me it happened. Two radios + amp end up to same freq, and just few VOX TX clicks made the receiving radio deaf. by Jussi-Pekka, OH6RX

Solution: I assumed (from block diagram) that the tuner main unit didn't fail and that it has be to related to RF-unit. I followed schematic from input (from tuner main unit) until to BPF section and measured all semiconductors which were connected to input signal path. I found only one PIN diode had failed (disconnect), D1056, 1SV271 Toshiba pin diode. IRmax (reverse) with VR 50V only 0,1uA.    VF 50V and IF 50mA. Just in case I measured the whole BPF section PIN diodes, to be sure that it was working. Opening/closing the radio takes quite a lot of time. No other failed components. For checks, you don't have to close all screws and blocks, just make sure that loosen parts wont make any more damage."

                PICTURE OF THIS REPAIR. CLICK ON ANY PICTURE TO DOWNLOAD A HIGH RESOLUTION PICTURE