Microwave Modules 144/30 repair - UK Vintage Radio Repair and Restoration Discussion Forum

Malcolm G6ANZ · 3rd Jun 2025, 4:34 pm

I bought a Microwave modules 144MHz power amplifier, 144/30. This will give 30W out for 1W in. Fairly old but interesting. Anyway powered up and went to transmit and....nothing on the output. The built in preamp worked though.
I found a circuit on the net and concluded that one of the changeover relays was not pulling in. I opened up the case and took the top off of the relays so I could see what was happening. Sure enough the changeover relay from RX to TX was not doing anything. Close inspection showed that there was a lot of green stuff near one end and I could just make out a break in the wire. So I unsoldered the relay from the PCB and removed all the contacts to gain access to the coil.
Close look with a magnifying lens showed that there was a break where the green stuff was. I carefully cleaned the area and lifted both ends of the winding clear. The insulating lacquer was scraped and both ends tinned. Then a short heat with the iron and the joint was made.
There was now continuity on the coil. I rebuilt the relay and soldered it back into the board. With new heat-sink compound on the PA transistor I fired it up. With 1W in I now had 25W out into a dummy load.
I could have bought a new relay but where's the fun in that.

Malcolm G8KGH

VT FUSE · 3rd Jun 2025, 7:49 pm

I think you could term that a lucky break!
Great that these M Modules are fixable. Well done to find the problem.

Mike.

Phil G4SPZ · 5th Jul 2025, 5:29 pm

Nicely done!

3rd Jun 2025, 4:34 pm	#1
Malcolm G6ANZ Octode Join Date: Feb 2006 Location: Bristol, UK. Posts: 1,138	Microwave Modules 144/30 repair I bought a Microwave modules 144MHz power amplifier, 144/30. This will give 30W out for 1W in. Fairly old but interesting. Anyway powered up and went to transmit and....nothing on the output. The built in preamp worked though. I found a circuit on the net and concluded that one of the changeover relays was not pulling in. I opened up the case and took the top off of the relays so I could see what was happening. Sure enough the changeover relay from RX to TX was not doing anything. Close inspection showed that there was a lot of green stuff near one end and I could just make out a break in the wire. So I unsoldered the relay from the PCB and removed all the contacts to gain access to the coil. Close look with a magnifying lens showed that there was a break where the green stuff was. I carefully cleaned the area and lifted both ends of the winding clear. The insulating lacquer was scraped and both ends tinned. Then a short heat with the iron and the joint was made. There was now continuity on the coil. I rebuilt the relay and soldered it back into the board. With new heat-sink compound on the PA transistor I fired it up. With 1W in I now had 25W out into a dummy load. I could have bought a new relay but where's the fun in that. Malcolm G8KGH Attached Thumbnails

3rd Jun 2025, 7:49 pm	#2
VT FUSE Heptode Join Date: Aug 2010 Location: Malvern, Worcestershire, UK. Posts: 796	Re: Microwave Modules 144/30 repair I think you could term that a lucky break! Great that these M Modules are fixable. Well done to find the problem. Mike.

5th Jul 2025, 5:29 pm	#3
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,903	Re: Microwave Modules 144/30 repair Nicely done! __________________ Phil Optimist [n]: One who is not in possession of the full facts