[Hammarlund] SP-600 Mystery Solved

[Bob Young]

I think finding a finishing nail in a radio's circuitry is always cause to 
give it a closer look,

Bob young
Millbury, Ma
KB1OKL


>From: Carole White-Connor <carolew at bellatlantic.net>
>CC: hammarlund at mailman.qth.net
>Subject: [Hammarlund] SP-600 Mystery Solved
>Date: Sat, 17 Mar 2007 19:50:26 -0500
>
>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
>
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