Ham Jumbo MK1 Channel change switch wiring info

[26DW429]

Hi all I have a MK1 Jumbo PTMB059COX with sub board PTOS006AOX. There was an eprom & it went wrong so i removed it & put it back to standard. With a lot of perseverance I eventually got the 6 PLL02 programming connections right pin 10 to 15 PLL02 & the channel switch common.

It works perfectly missing the 5 Alpha channels as it should & correctly stepping the odd channel spacing in between channels 22-26. I bought a UK 40 EPROM from spectrum & fitted it, but only so many of the channels are correct. I have been wondering if there is another way of wiring the channel selector to obtain the correct channels as it is now but will work correctly with the UK 40 EPROM. On the small channel board PTSW026COX there are connections marked P1 to P8 & PB which is the common connection 5Volt & on the PLL sub board there are connections P1 to P6 & M (mixer) but M hasn't been touched. Most match up P number to P number ect.

I would expect if the channel switch is working correctly with the PLL02 I would have thought it would program the EPROM correctly too. BTW I returned the EPROM for test & was sent back reported OK. I have done a lot of work on this Radio in the past almost 8 Years making Her sound great on FM/SSB & other improvements. I have modded Her now with a 6 way band switch at the moment LO MID HI HI HI & I am waiting for 2 custom made Crystals from Quartslab both in the 9 MHZ range to give Triple Lo & Super LO giving 25.615-28.305. Anyone know if there is a different way of wiring as I would be most grateful. Info or Images if possible. Thanks 26DW429 David.

[Mitch]

I guess nobody does this sort of thing anymore by the lack of response, I used to do this sort of thing nearly 40 years ago now and found the limits of these chassis. While I admire your determination and enthusiasm and we all need a hobby, you are going to struggle with all these channels tbh.
You might want to put the kettle on for this

The legal board can only be wired one way correctly so you'll have to check all the pin wiring in the radio and jumper pad settings on the PCB, they could be wrong and even if the wiring is right it still won't work properly with wrong PLL code setting. You will have to check that the PLL and channel changer codes tally too, you may even have a whisker or solder blob somewhere it shouldn't be, you need to check it all in 'UK off' mode, normal channels, pin by pin, channel by channel. That's how I'd do it anyway. Hint: Ch1 mid all PLL pins are on (+5v), pin 15 changes most and pin 10 the least when changing channels.

Channel expansions for low bands are going to be a pain as well, for several reasons. One is the rigs bandwidth limitations, it is after all basically only a modified 40 channel radio (think Colt Black Shadow 485 board) and struggles to do 120 channels as it is. Then there's the VCO, the band switch voltage change won't help locking range either, the best option is replacement with a Spectrum VCO block and disconnect band/volt swithing (switch wire goes to 5v PLL supply). The output is a problem too. The final output stage isn't designed for 120 let alone 200 channels so performance will be compromised and lower power over the channel spread. The biggest problem here though is the mixer outputs (T2, T3, T4 & T5), you will have to put switched trimmer caps across them the same way they do it in Supertar/NATO 2000 (PTBM125/131A4X) type board so they switch in on low bands and then tune the trimmers for low channels band spread, tune the cans first for mid and hi bands though. Get a circuit diagram for reference and just solder the bits PCB side, it'll work. On a side note, the Spectrum eprom will do -40 low channels but you have to cut more PLL tracks (7, 8 & 9) and put links in, so in theory you can get 6 bands with 3 crystals. It's a lot of effort though.

Now we come to the crystals, mmmm. Not the best circuit by a long way, poorly designed but kinda works. The biggest problem here is the wires, the crystals themselves, and the trimmers, are connected directly to the band switch so wire lengths, switch contacts, nearby parts and stray RF can all affect tuning and stability. Putting extra crystals in will affect the ones already there and tuning can become difficult or even out of range. The varicap diodes are also not in the best place for the tune/clarifier circuit and LSB switching (though you can use LSB switching for UK band shift with some diodes added). I used to make my own PCB's back in the day and I made a copy of a later PTOS012AOX board for 6 crystals + clarifier and tune, using the 20 (&19) Mhz crystals then switched bands using volts like later radios, much more stable and tune range can be easily extended with low value chokes (2.7-3.3uH) as well. But that's another story....

Hope that's some help (if you haven't fallen asleep yet) so good luck with the mods. I don't have any pictures (too long ago) and I've probably forgot most of what I knew back then (1980's) but it was interesting at the time and spares were readily available then as well.

[26DW429]

Cheers i installed the spectrum VCO block recently & i know what you mean about the trimmers going through the band switch viia ground. Could do with seeing pics of channel selector wiring