The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Radio Make = Ham International
Radio Model = Jumbo Mk1
PCB number = PTBM059COX - Main board
PTOS006AOX - VCO\Crystal board
PTPW007COX - Power Supply board
PLL number = PLL02A

Test gear available: TRIO FC 756 frequency counter (yes I finally upgraded from the zetagi c57! lol), basic scope, swr/power meters, dummyloads


The radio was down on power and was slightly off frequency, so i decided to do a full realignment on it. I got to where it said:
"set radio to AM, set channel selector to 60 (mid band), adjust RV-8 for 5W RF power"

When I adjust RV-8 nothing happens, no change in power at all. I also notice that there is no swing on external meter, and very little swing showing on internal meter whilst modulating on AM. I have tried 2 external power meters and replaced the pot at RV-8 with no change.

Upon looking at the schematic, it appears that RV-8 is part of the SSB AGC circuit and not related to AM carrier power at all... so, is the service manual wrong or is the schematic wrong or am i just mis-reading them both?

Other than this radio appears to be working fine, although i notice that SSB PEP is also low at around 4 watts as opposed to 12 watts on FM. however i havent finnished the allignment yet so that may not be related to this issue.

Anything else that may be of help?: This radio had been previously owned by a "mod-jocky" and there are mods all over the place... there is an eprom to give uk40, extra crystal added to give lo-lo, variable power mod, beep switched, fm audio mod, K40 microphone mod and other little mods i dont recognise. not all mods were done neatly, some could have been done by a trained monkey

Norm,
You said it's got variable power, so the adjusters two large white pots may have been removed, they are the pots for high and low power in AM and FM mode and I think one is VR8. The VR8 your talking about is on the main 059 board the other two are fitted on the chassis left side in front of the PSU.
Don't worry I know, I've been there before that's how I know about them.
If it's got an Eprom then why didn't they just add more bands with the Eprom instead of fitting more crystals
Dave.

Hi Dave, thanks for your quick reply.

Yes the radio still has the 2 large wirewound pots on the underside near the power supply board... they are both set at maximum at the moment... i had been wondering what they are for, so thanks for that info.

It has me puzzled also, why with an eprom the guy would have added an extra crystal to get lo-lo... the only thing i can think of is that the lo-lo mod was done before the eprom conversion and so it was left in? who knows?

The standard hi/low power switch has been cut and bridged on permanant full power, with the new variable power pot drilled into the rear of the radio alongside the beep switch.
The wires have been removed from the "tune" pull switch for some unknown reason and nothing uses that switch (i wondered if that had anything to do with the eprom conversion) the rotary tune control works still.

Basically this radio is in a hell of a mess and is gonna take a bit of sorting to put it completely right, but i cant complain coz i got it for free

I'll post some pics of the wonderful mods sometime and then we can all see just how not to mod a jumbo..lol!

If it were me, I would undo everything and return it to original first (apart from the EPROM board), and then go from there, possibly re-modding anything that is needed.

Hi Scott,
Thats a good plan, removing all the mods and putting the radio back to standard i may end up doing that eventually if i cant work around the mods and get the radio working properly.

I've already had to re-wire the beep switch because it was wired wrong and had just cut the audio, so the delay was still there and I've also re-done the variable power mod as that was faulty...

I plan to re-wire the "Tune" pull switch too at some point and certainly tidy up all the mods ect

Would be good if I could talk to the Guy i got the radio off and ask "why did you do it like that?", but unfortunately i cant, so i'm working blind. oh well, I do love problem solving

Also i've just found out that the service manual i've been following to align this radio (PTBM059COX/PTOS006AOX) is not the correct one for the Jumbo (although it is very similar). The Jumbo service manual i've just found has a couple of differences, which makes a heck of a lot more sense.

UPDATE: Thanks Guys! After a long day in shed, radio is now aligned and a few more of the mods have been tidied up. Please now see my new topic "Ham Jumbo No swing AM"
http://www.radiomods.co.nz/forum/viewto ... f=1&t=2914
once the swing problem is fixed, this radio is pretty much sorted (apart from just needing to tidy things up)