Perhaps one or more of you more knowledgeable folks are able and willing to assist me! I have had an AR-1500A for many years, I built it in 1974. A couple of years ago, I decided to replace all of the caps, and did so. i inadvertently reversed the power supply caps, which of course blew, taking the four rectifier diodes and one transistor with them. I replaced all of the burned items, and now the power supply is fine. However, there are now other problems! When using a 60 Watt light bulb in series with the AC mains, the bulb burns brightly. I removed each PC board, using the process of elimination, and learned that with the Multiplex board and the FM IF board removed, the bulb now glows normally. Of course, I have no FM, that is to be expected. I then temporarily replaced each of the two boards, with known good boards from another AR-1500A, and ditto, no FM, so I now also suspect a problem with the FM tuner additionally. I thought I'd work on the boards first. I began with the IF board, checked each resister and transistor, removing each from the board. All check good, with the exception of Q204 and Q205. Both have been burned. Nothing else appears to be burned. Nothing appears burned on the Multiplex board, but I have not as of yet checked any components. I did remove the six electrolytic caps from the Multiplex board, and with them out of the PC board, I can reinsert the board into the AR-1500A, and no excessive current draw, but of course, not FM either. And with both Q204 and Q205 removed from the FM IF board, I can also reinsert that board as well, with the same outcome, no FM. Amplifier sections works normally, as does AM. I only have a variety of multimeters for testing, perhaps one or more of you could direct me to a suitable capacitor tester for purchase. I see many advertised, most require 1-2 months from China to be received. Any comments at all would be appreciated. Thanks much
Howard Spivak
Howard Spivak
I have attached schematics for the AR-1500, rather than the AR-1500A, as this is what I have in PDF format, however, with regards to the two PC boards about which I'm inquiring, the two are virtually identical.
Capacitor testers are useful for determining capacitance at 1-2 v test voltage perhaps, but do not tell you a thing about shorts occuring at higher voltages. I bought mine from parts-express, but after the burglar carried it and everything electronic off, they have not been supplying them again. Newark wants like $600 for a B&K, sort of overkill for an amateur shop.
I say, all those unique early 70's parts in the AR1500 FM area make this a difficult candidate for restoration if FM is where the problem is. Dual gate Nfets 40673, Ua703 amp, MC3017 decoder, CA3012 quad long tail pairs? Where would you buy those? Even the Jfets, conveniently n channel, there is no idle current spec on them. I've had decent luck with old receivers containing only bjt's. A major power supply surge at the start makes this repair somewhat of a unicorn hunt. And there is a whole list of test equipment required to work on FM decoders if there are any major replacements. I limit my FM repairs to replacing the 0.47 uf and 1 uf electrolytic caps and maybe cleaning some interboard contacts. Tuning out of this thread, I am afraid.
I say, all those unique early 70's parts in the AR1500 FM area make this a difficult candidate for restoration if FM is where the problem is. Dual gate Nfets 40673, Ua703 amp, MC3017 decoder, CA3012 quad long tail pairs? Where would you buy those? Even the Jfets, conveniently n channel, there is no idle current spec on them. I've had decent luck with old receivers containing only bjt's. A major power supply surge at the start makes this repair somewhat of a unicorn hunt. And there is a whole list of test equipment required to work on FM decoders if there are any major replacements. I limit my FM repairs to replacing the 0.47 uf and 1 uf electrolytic caps and maybe cleaning some interboard contacts. Tuning out of this thread, I am afraid.