[Heathkit] Heathkit uMatic SA-5010 Memory Keyer - fun n games

[Bill Cromwell]

Hi,

Long ago a SA-5010 keyer followed me home from a hamfest and I used it 
for a long time. One day it just plain stopped working and I supposed it 
might be the internal batteries (no way). I set it aside temporarily 
(for several years). I got it out and took it apart. I do have the 
original manual that I got with it. I already had purchased new button 
cells for the memory backup. I seemed to not be getting power and the 
manual and the troubleshooting hints I found online suggested the bridge 
diodes. I unsoldered one end of each one to determine which one was bad. 
They were all good. I put the bridge all back together.

I noticed at the far end of the circuit board there was a lot of 
corrosion and one of the ICs there had pins that were green with 
tarnish! I cleaned them all up and did the same for each and every IC 
even if they looked clean. I cleaned up around where the touch paddles 
go (I never had those). Put it all back together and fired it up. It 
came on but sent continuous dits. I took it back apart and cleaned 
around the touch paddle contacts more thoroughly. I reassembled it but 
this time it didn't come on.

I disassembled it yet again and found one of the wires had come 
'unglued'. I resoldered that and reassembled. It came on! No dits! I 
selected code practice at 18 wpm and it started spewing out code 
practice at what seemd to be about 18 wpm. Sweet. I picked it up to 
change the pitch and volume (screwdriver adjustments underneath). The CW 
stopped and smoke issued out of a slot in the case :(

I redisassembled it or did I unreassemble it. The previous undisassembly 
I had installed the cardboard insulation sheet *backward*. The collector 
+ got shorted to collector - through the cast aluminum housing and 
burned a hole in a circuit trace. Rats! A solder bridge restored the 
trace. Back together one more time. It worked again. This time I changed 
the pitch a little and slightly increased the sidetone volume. When I 
set it down it stopped again but this time at least there was no smoke. 
I know now that I will have something to do tomorrow or Tuesday. I am 
getting too familiar with the inside of that gizmo. I expect to find yet 
another wire has come unhitched. I probably will never, ever put that 
cardboard insulator in backward again <evil grin>.

Aside from what I have already found do any of you have some gotcha's or 
hot spots to watch for with those keyers?

73,

Bill  KU8H