Ham International Jumbo repair project

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Lektroid
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Call Sign: ID808

Ham International Jumbo repair project

Post by Lektroid »

Hi all, I have a rather ill Ham International Jumbo, It's never worked since I've owned it so no idea what casued the problem. The radio appears to have been modified since it has a larger Vreg and a 3 pin crystal filter soldered to the back of the main pcb. A couple of wires were off, one of which I managed to trace from various photos I've looked at, the other was a purple wire going to somewhere near the middle of the main PCB (solderside), although I'm not sure if the removal of the wires was part of a mod?

Basically when I switch it on, it beeps breifly but very loudly, lights up, makes the expected white/pink noise, but does not transmit or receive anything. It also only does the straight 40ch in all modes & freq ranges instead of the 80 in mid band. The LEDs work as expected, but nothing shows on the meters.

I've connected the frequency counter on my oscilloscope into the freq out socket, but it has a very weak signal, also tried connecting my freq counter to TP1 as per service manual, which also has a very weak out with with +25V DC offset, after aligning the trigger, I'm getting readings closer to what's in the service manual, except the high band, which gives spurious readings, although I personally think the problem is further back though, as the PSU was set to chuck out just over 15V instead of 13.8V, I've tweaked it down now, but I'm wondering if it's taken out one or some of the weaker components in its wake?

I wonder if anyone can help me get this radio working, even if I can just get the sidebands working I'd be happy.

Many thanks in advance & 73's
normal
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Re: Ham International Jumbo repair project

Post by normal »

Which board is in it? PTBMxxx
Pinksnake
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Re: Ham International Jumbo repair project

Post by Pinksnake »

Hi fella remember that u have another jumbo there for helping u trace the wires and such like.. Good luck tho.
Lektroid
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Re: Ham International Jumbo repair project

Post by Lektroid »

Pinksnake wrote: 28 Jan 2022, 15:02 Hi fella remember that u have another jumbo there for helping u trace the wires and such like.. Good luck tho.
After comparing with the other Jumbo (which you can see is factory soldered), seems some clown decided to rewire it completely wrong. basically about 30% of the wires are connected to the wrong places, also the diodes and resistors which were soldered to some of the wires have been removed.

Time to get amongst the spaghetti...
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14CS06
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Re: Ham International Jumbo repair project

Post by 14CS06 »

Photo Collector CB RADIO
Lektroid
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Call Sign: ID808

Re: Ham International Jumbo repair project

Post by Lektroid »

Here's the latest, I've wired mine up to the factory wiring copied from the donor jumbo (you can tell from the solder joints that all wires were factory), but it still didn't work. I looked at the 2166 which tested fine on my Peak DCA, I then checked the 1969 which was reading as a diode, so I replaced it, but it is still not working. I've also replaced the TA7205AP as I'd read somewhere these are troublesome. Other than that I have no idea where to look. the static noise increases when the antenna is plugged in, so it seems like it should be working, but no Rx or Tx. There is a very weak signal coming from the Freq. out, and when I hooked it up to the freq counter on my scope it gives spurious readings.

If anyone knows this radio and might have an idea what could be wrong, it would be great to hear from you...
Many thanks in advance & 73s
lbcomms
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Re: Ham International Jumbo repair project

Post by lbcomms »

Lektroid wrote: 08 Feb 2022, 18:11 There is a very weak signal coming from the Freq. out, and when I hooked it up to the freq counter on my scope it gives spurious readings
Sounds like the PLL / VCO is either faulty (very common fault with this radio) or way out of alignment after an attack of the golden screwdrivers.

In the 2nd post before this one, the second link is for to the manual that has servicing / alignment instructions (see page 12).
Can you achieve the voltages and frequencies listed, and if not, what voltages / frequencies do you see at the stated points?
John555
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Re: Ham International Jumbo repair project

Post by John555 »

lbcomms wrote: 09 Feb 2022, 10:33
Lektroid wrote: 08 Feb 2022, 18:11 There is a very weak signal coming from the Freq. out, and when I hooked it up to the freq counter on my scope it gives spurious readings
Sounds like the PLL / VCO is either faulty (very common fault with this radio) or way out of alignment after an attack of the golden screwdrivers.

In the 2nd post before this one, the second link is for to the manual that has servicing / alignment instructions (see page 12).
Can you achieve the voltages and frequencies listed, and if not, what voltages / frequencies do you see at the stated points?
I agree, have you checked the VCO voltages? assuming this is the mk1 (059 board) they should be 3.6, 3.7 & 3.8 on ch 1 in low mid and high respectfully. have a good look at the VCO core but be careful they are very fragile and quite often cracked etc. spectrum communications to a replacement for the green block VCO - solders straight in, ive used a few and the work fine

Also worth checking TP4, adjusting T1 for max signal to make sure the mixer oscillator is good.

Good luck! ive also got a sick jumbo ive never quite been able to drag on frequency so I know how frustrating it can be...
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