New member here, 40+ years experience with bench test equipment. My day job is Systems Engineer with automated test systems.
Last weekend I was browsing a guitar show and found a box of various bench test instruments labeled "make an offer". Pulled out a Sencore LC-102 thinking "why does this look familiar?" Included the power supply, test lead (with missing clip), and the test lead adapter (but not the hold down rod). A capacitor analyzer would be useful on my workbench. I opened my wallet to the seller that had less than $60 inside -
he took $50 for the LC-102. He says that it does work.
It was later that night that I realized a) what their value is on the market
b) the demand for these things, and c) from discussions in this forum that these units have a lot of common malfunctions. From pictures of other LC-102 units, the panel on mine has yellow aging so it must had seen a lot of sunlight. As you can see from my website
http://www.analoguediehard.com I am not intimidated by instrument restorations.
Soooo... after printing the manual, schematics, patents, tech tips, calibration procedures, circuit descriptions, references in this forum (THANK YOU!), and organizing them all in a three ring notebook, I reviewed the unit operation and prepared to fire it up - expecting the worse.
Power on self test - PASS
Test Lead zero test - PASS
Test Lead short test - PASS
LCD Display test - PASS
Other than the test lead needing a replacement clip,
this thing is free of defects! I popped the hood - by the datecodes on the ICs and other components, this unit was built in 1996. So it's a fairly late model. There's a bunch of jumper wire modifications combined with floating components, I haven't documented them yet.
Firmware eprom is v17. Expecting to find eight of the Fairchild relays known to fail, I only found five.
In place of three of the Fairchild relays are American Relay Inc substitutes Z051B300R0A (L4) and Z051A550R0B (L1, L9). The relays are cylindrical (you're not prying these puppies open!), are axial pin-for-pin direct replacements, and have 1996 datecodes like the rest of the unit. They show no sign of solder reflow/repair so they must be original from the factory.
Hello...!
Did Sencore identify a more reliable substitute late in the product life?!?American Relays Inc was acquired by Standex Electronics in 2021. I tried various search terms to locate any info on the American Relay "Z" series and came up empty. None of the usual suppliers (Mouser, Digikey) show any available.
One thing I have learned in restorations: if your unit has the 4xxx CMOS ICs made by RCA, replace them with new NS or TI CMOS. The RCA CMOS of the 70s/80s have a history of rotting substrates due to chemical interactions causing a short to ground, and according to my RCA databook they do NOT have overvoltage protection on the input pins now standard on modern CMOS.