SQLGuy
Member
Hi folks,
I was thinking of building an SQ decoder, but had a number of disruptive things come up, and, the other day decided to see what was on eBay. There was a guy with an "as found", only known to light up, SQ-W. I negotiated and bought it for $220 + $18 shipping, rather than the $350 + $18 he was asking. Sadly, but not surprisingly, it's not working. No sound in most modes, pass-through discrete gives a pulsing bass thump with a lot of noise. And the power lamp seems to have lasted only long enough to light up once.
Opened it up and found a bad solder joint on the main capacitor, but resoldering it didn't help. First look at voltages didn't look right... will take another look at that.
The good news is that it's in good shape - doesn't look like anyone has worked on it before - physically just a couple of scratches and missing feet. The other good news is that all the components are generic, discrete, devices, with the exception of the four prehistoric ICs. They are Motorola SFC6043 devices... which I couldn't find anything about... but the schematic says, "MFC6043 or MFC6040." The MFC6040 does have some info online, and those seem to be available from eBay. Apparently, they're not exactly op-amps, but voltage-controlled attenuators.
So, first question is whether anyone has experience repair or overhauling these. The electrolytic caps are all Matsushitas. I've have very good experience with their caps, but these ones are still 44 years old. I'm thinking to pretty much shotgun the caps in favor of some 21st century Nichicons. Any ideas on a suitable 6.3V lamp for the power indicator?
Any other ideas on what else typically goes bad in these things?
Thanks,
Paul
I was thinking of building an SQ decoder, but had a number of disruptive things come up, and, the other day decided to see what was on eBay. There was a guy with an "as found", only known to light up, SQ-W. I negotiated and bought it for $220 + $18 shipping, rather than the $350 + $18 he was asking. Sadly, but not surprisingly, it's not working. No sound in most modes, pass-through discrete gives a pulsing bass thump with a lot of noise. And the power lamp seems to have lasted only long enough to light up once.
Opened it up and found a bad solder joint on the main capacitor, but resoldering it didn't help. First look at voltages didn't look right... will take another look at that.
The good news is that it's in good shape - doesn't look like anyone has worked on it before - physically just a couple of scratches and missing feet. The other good news is that all the components are generic, discrete, devices, with the exception of the four prehistoric ICs. They are Motorola SFC6043 devices... which I couldn't find anything about... but the schematic says, "MFC6043 or MFC6040." The MFC6040 does have some info online, and those seem to be available from eBay. Apparently, they're not exactly op-amps, but voltage-controlled attenuators.
So, first question is whether anyone has experience repair or overhauling these. The electrolytic caps are all Matsushitas. I've have very good experience with their caps, but these ones are still 44 years old. I'm thinking to pretty much shotgun the caps in favor of some 21st century Nichicons. Any ideas on a suitable 6.3V lamp for the power indicator?
Any other ideas on what else typically goes bad in these things?
Thanks,
Paul