Midland 7001 PTDM121D4x no AM or FM TX?
Posted: 18 Oct 2023, 14:08
Hello all
I wonder if anyone can help with this one.
I have an AM/FM/SSB Lo/Mid/Hi Midland 7001 that uses the PTBM121D4x chassis and it will not TX on AM or FM, it will on both USB and LSB at a bit higher than normal power (which could just be simple alignment) but no AM or FM TX.
Rx and Rx audio on all modes and channels is fine and SSB TX audio seems to be fine.
I replaced Q36 the 2SD837 as a matter of course and the one that came out measures fine but after I replaced it with a brand new one, the radio will tx on AM and FM at low power (say 2w) for a very short period where the output will decrease until it drops off completely. the voltages around Q36 are very low (as in 2V at best on emitter and base) and not very stable (ie continually dropping as it stops transmitting), apart from the collector which is stable at 13.6V whether in TX or RX on AM or FM and before and after it stops transmitting, I haven't checked on SSB.
I'm not sure this is particularly relevant but when I fired it up originally it had no TX and I thought I'd replace the VCO with a wide band version as I was intending some other mods and again TX came back at low power and then promptly faded off in exactly the same way as when I started digging a bit deeper and replaced Q36. I hadn't checked any voltages around Q36 at this time.
I have seen mention of the through holes on the board being an issue and the board on this one is very clean indeed so I will see if I can see any issues here, and I also saw someone ask what the voltage on post 11 was on a similar thread when in TX so what voltage should I be seeing there in TX?
Apart from the through holes I'm going to replace C181 but other than that any other suggestions would be a great help as I'd love to get this one going again, the skips in so I want to use this one mobile if I can. I've also got a misbehaving Nato to get to after the Midland but one job at a time as they say.
Thanks in advance.
I wonder if anyone can help with this one.
I have an AM/FM/SSB Lo/Mid/Hi Midland 7001 that uses the PTBM121D4x chassis and it will not TX on AM or FM, it will on both USB and LSB at a bit higher than normal power (which could just be simple alignment) but no AM or FM TX.
Rx and Rx audio on all modes and channels is fine and SSB TX audio seems to be fine.
I replaced Q36 the 2SD837 as a matter of course and the one that came out measures fine but after I replaced it with a brand new one, the radio will tx on AM and FM at low power (say 2w) for a very short period where the output will decrease until it drops off completely. the voltages around Q36 are very low (as in 2V at best on emitter and base) and not very stable (ie continually dropping as it stops transmitting), apart from the collector which is stable at 13.6V whether in TX or RX on AM or FM and before and after it stops transmitting, I haven't checked on SSB.
I'm not sure this is particularly relevant but when I fired it up originally it had no TX and I thought I'd replace the VCO with a wide band version as I was intending some other mods and again TX came back at low power and then promptly faded off in exactly the same way as when I started digging a bit deeper and replaced Q36. I hadn't checked any voltages around Q36 at this time.
I have seen mention of the through holes on the board being an issue and the board on this one is very clean indeed so I will see if I can see any issues here, and I also saw someone ask what the voltage on post 11 was on a similar thread when in TX so what voltage should I be seeing there in TX?
Apart from the through holes I'm going to replace C181 but other than that any other suggestions would be a great help as I'd love to get this one going again, the skips in so I want to use this one mobile if I can. I've also got a misbehaving Nato to get to after the Midland but one job at a time as they say.
Thanks in advance.