Well, I needed to get back to my recently repaired Kenwood TS-790 as it developed a new problem... first ATV label (yes, there is an ATV label !) blinked from time to time, with no apparent reason and, sometimes, it kept lit for a long period. I checked schematics and got lost when trying to find the origin of the signal...
But eventually it got worse: yesterday, while talking in a local QSO in 2m FM with the 790, I found a very curious thing. My 790 was SLOW to react to key presses, frequency change and even PTT!. Yes, there was a variable delay, from zero to some seconds, for the unit to execute what it was asked to do... Having worked for years in digital electronics, I thought the CPU was receiving some kind of interruption which made it work slow and even lose some commands or inputs to it. Immediately I thought of a backup battery leak damaging the circuit...
Here you have a low quality video of what happened. Sometimes dial is not updated but frequency changes. Also, F key is erratic:
So I got the 790 back to the workbench and, yes, there it was!. Battery, which measured a perfect 3.32V, had leaked and damaged some PCB traces below it. I don't know how I missed this when I fixed the unit!
This is what was below the battery...
I got the bad battery out, cleaned the acid residue and added a battery socket and a 2032 3V battery which is smaller capacity than the original one but lots easier to locate and, with the socket, a breeze to replace next time. I used Renata swiss made battery and holder as they are IMHO one of the best batteries available.
Note that the battery holder was not a perfect fit so I needed to add some wire to connect one of the poles to the PCB. But, all in all, it is lots better than the original soldered battery.
I tested the rig and it worked almost flawlessly. Yes, there is now a different fault which I need to further investigate... Now ATV icon does not light and rig reacts fastly to keypresses, PTT and such. But now ON AIR LED is sometimes behaving strangely: it sometimes does not light and sometimes keeps on even when PTT is not active (but rigs go to TX and RX as it should). So I need to check carefully how ON AIR LED is activated and check the unit to locate the fault. I will do it when I install the UT-10 1.2GHz module I recently bought... so keep tuned for a further update :-)!