Ham Jumbo no TX

[mutley]

Hi all,

Recently bought a Ham Jumbo Mk1 PTB059C0X with a known TX fault.

The radio receives fine but doesn't switch to TX. When Mic is keyed, the relay kicks across and mutes the speaker, but the needle still shows the receiving signals, there's no TX light and zero output.

So I'm fairly sure it's the TX/RX switching area. VCO is fine and have the 10.240 at the PLL.

Just wondering if there are any common faults that cause this?

Cheers

[warhorse]

Hi, cap 11 is known to go faulty - 56 pico on vco board

[warhorse]

Even if your vco had failed you would still if you hook up a test probe around the predrive stages get a reading on a freq counter in Tx!

[mutley]

Thanks Warhorse, will check that first.

Cheers

[bitbang]

Common issue back in the day was the relay itself and bad solder joints on the small relay board. If you have a multimeter check D48 + D49 go low when PTT pressed. If okay check Q40, Q42.

[mutley]

Ah thanks bitbang, good call. I'll have a proper look at the relay board at the weekend.

I've also ordered Q40-43 replacements just in case. Do you know what all the diodes around the TX/RX switching are? Not removed them but see there seem to be two types..

Looking at D44-49 and D52

Cheers

[mutley]

Found a schematic with the parts so can hopefully trace it all out now.

Cheers

[14CS06]

Hello

manual

https://cbtricks.org/radios/ham_interna ... mbo_om.pdf

@+
Claude

[bitbang]

1n4148's or any other similar diode will work in these positions, most scrap CB boards have some if you don't have any new ones to hand.
Also opening up the relay and using a sheet of paper with a drop of switch cleaner on it to clean the contacts was done back in the 80's

[mutley]

Thanks guys,

Getting there slowly... seems it's been hacked about a bit in the past. Wires are different colours and the Roger Beep board's had all wires removed. I think the relay board was wired wrong and after tracing wires and using the schematics i *think* I have it. It TX's now when mic pressed at least, but with very low power, and the modulation light flickers when talking into the mic. Didn't go any further as it was getting late yesterday.

Are there jumper wires on the small relay board as standard? The schematic tells me to wire to pads with no connections to anything so I've improvised.

Since my "improvisation" though, the channel readout's gone funny.. think I've got some extra segments lighting up making it look like 50+ is now 90+ so more troubleshooting necessary

Cheers

Nick

[14CS06]

Hello

Roger Beep

pics of my jumbo I

@+
Claude

[mutley]

Hello

Roger Beep

pics of my jumbo I

@+
Claude

Thank you Claude

[warhorse]

Hi good claude put the beep board up'' roger beep board from left pins 1.2.3.4.5. pin 6 not used! white wire = (1,audio-bleep or mic audio) (2, 13.8v +) (3,tx in, from mic tx pin),

(4, Earth ) (5,tx out which when switched goes low in tx - ) if your beep board isnt working by checking the volts and its not switching you can bypass the beep even in circuit by soldering the tx pin to where the pin 5 blue wire
goes on relay board, the relay works in rx and tx.. top and bottom pins are earthed,) next pins top is 13.8 bottom is ((negative)) next pins along top pin is tx, bottom is rx audio from speaker (( the negetive pin below the 13.8 volt pin of relay coil of the coil in relay is the trigger for the tx pin either from pin 5,(blue wire) of beep board of tx pin on mic socket...if you find even before you get a bleep through your speaker just means the return wire of pin 5 isnt triggering the relay to take audio away from the speaker.....lol