I think I’m finally to the point of being able to say I’ve completed my first conversion of a 900MHz Maxtrac. The radio originally started out as a trunking multi-channel (talkgroup) radio. I replaced the trunking PROM with a conventional PROM and went through the process of blanking the radio and re-aligning it. Details on the process are available here.
The only part of the alignment I was unable to complete was the TX deviation as I had no way to inject audio with the programming cable (non-RIB) that I’m using. I’ve got a schematic and I think I can build a jig to allow me to inject the audio, so I’ll revisit that soon. I also have a few more of these radios to convert. I did not replace the filters as part of this operation. I do have some 915MHz ceramic filters that I was able to track down in the UK, but I’m trying to use those sparingly.
After I’d completed the re-alignment process, I ran the radio on my bench for a day or so and even made a couple of QSOs. Then I took it out to install it in a buddy’s car, and I had no receive. Brought it back to the bench and the problem was still here. On the suggestion of a fellow Ham, I cracked it open and checked the steering voltages for RX/TX. Sure enough, they were low. So I went though the process to bring up the voltages outlined here.
I buttoned the radio back up, including putting the cover back on the VCO, and the radio would neither transmit or receive. At this point, I opened it back up again and checked the steering voltage. It was 8.88VDC on either RX or TX, which is WAY to high. So I cracked up on the VCO again, and removed some of my silver circuit ink. I can only surmise that when I was heating the VCO case to replace the cover, some of the silver “ink” flowed a little bit and raised the voltages. I found that the steering line voltage is extremely sensitive to even the most minute amount of “ink.” After playing around with it a while, I was able to get the voltages in line for both RX and TX. So I reassembled the radio AGAIN, and so far so good.
