[Hammarlund] SP-600 Mystery Solved

[Carole White-Connor]

I found and repaired the mysterious problem that was causing Bands 4 and 5 to go
deaf on the upper parts of the band. The troubleshooting was definitely strange.

1. When I first got this set, I gave it a careful visual inspection (for hidden
treasure, dead bodies, rodent effluvia, burned resistors and charred
capacitors). I saw that S-71, a 680-ohm resistor from the Frequency Control Unit
to S-3, was hanging loose. I re-soldered it before I even powered up the set. .

2. Today, I found out that S-71 was hanging loose for a reason. S-3 is the
switch that switches from variable frequency to fixed frequency operation. The
linkage between S-3 and the Frequency Control Unit shaft was malfuctionining. A
prior owner had tried to fix/frig rig it with a finishing nail. The fix/frig rig
didn't cause the linkage to work properly. It just prevented it from falling
apart.

3. If I understand the schematic correctly, S-71 is in the circuit when the set
is operating on a fixed frequency. Because of the linkage problem, it was in the
circuit at all times. Once I disconnected it, the set came to life on all bands
and on the upper parts of all bands. It now sounds like an SP-600 is supposed to
sound.

4. Moral of the story: visual inspection can be as valuable as test equipment.
If I hadn't noticed that finishing nail, I would have never figured it out.

Thank you all for you help!


Joe Connor