I knew it was a mistake putting the lid on properly.
Having restored the functionality of the frequency display I decided to run the radio for a few hours over the weekend to evaluate performance further. Still no tx, of course or any PLL locking on 28MHz but I knew that already ...
I was listening to a QSO on 7MHz this morning between a very strong Belgian station and a string of UK stations, most of whom I could hear reasonably well when I realised that the frequency seemed to be locked on to 7.150.0MHz. Tuning either side by a kHz or two made no difference to the display. I had a funny feeling about this, so I tuned up and down the band to find that lo and behold that the display was only displaying frequency to a 10kHz resolution!
To see whether this was a heat related issue I switched the radio off and let it cool down for half an hour or so, but on re-powering the fault was still present, so I have concluded that I have ANOTHER dead chip! More than likely a duff 7490 in the counter chain, and that's TTL not CMOS, so another theory goes down the pan.
It is now only sheer stubbornness which is sustaining my interest in this project. In all the years of building and repairing equipment, I don't think I've ever come across a project like this. Trying to fix up a radio with numerous faults is one thing (and what I thought I was dealing with here), but fixing one which keeps breaking seemingly randomly whilst under repair is quite something else. It's a case of either "nolum illigitimus carborundum", or chuck the bloody thing in the (recycling) bin! I don't give up easily though. What kind of trauma has this radio suffered in the past? It's anybody's guess.
Hi Martin, seems that this little blighter has gone through the mill since it had liquid spillage.
ReplyDeleteI like you once upon a time would never give in but it came to a point that i was bashing my head against a brick wall so when a client brought equipment in that had spillage then there was only on e answer and i think you know what that would be, after all all the major manufactures stated that once this had happened then the item was deemed to be unsafe and totally unreliable.
Were do you draw the line??
73
Ken G3SDW
Don't know Ken, it's only sheer cussedness keeping me going now, though I suppose there is always the "self training" aspect, plus the fact that I actually enjoy fixing stuff, normally.
ReplyDeleteA colleague in the pub the other night when appraised of my trials and tribulations wondered whether it's all power supply related as that is common to almost everything, I seriously don't think so but I have to keep an open mind.
At some point I was thinking about re-engineering the AVR board with its dreadful shunt regulators with something more up to date, but hey, I'm getting ahead of myself here!
Somehow i am inclined to agree with your mate, at this stage it must be considered. You like me with a problem like this is like a dog with a bone,won`t let go.
ReplyDeleteIt still gives me great satisfaction to get inside a piece of kit and smile when it is working again. Only this week i picked up off of ebay a non working 30amp Alinco SMPS just to keep my hand in but alas had it going in 10 minutes, all it turned out to be was a very bad joint on the mains input socket. So think i will put it back on ebay at least it is now working.
73
Ken