Joined: Jan Thu 01, 1970 1:00 am Posts: 137 Location: Charlotte, NC
Have a Radio Shack 12-697A transistor AM/FM cassette I'm looking at for a friend, guessing from some time in the '80s or '90s. Radio is dead on both bands, but the tape player works fine.
Just a quick look at the board, has a KA22471 IC for most all the radio functions, so I can do some troubleshooting from that datasheet, but would really need a full schematic.
I did Google around and found some original service manuals for sale, but at $20 a pop they're worth more than the set. Anyone have a similar schematic I could use a reference? I'm sure there must have been hundreds of AM/FM transistor sets that used this IC and had nearly identical circuits.
Joined: Jan Thu 01, 1970 1:00 am Posts: 137 Location: Charlotte, NC
Hmm, well unfortunately I don't have a user's manual for it either.
At this point I'm not sure there's much else I can do without a schematic. Have only 0.2vdc at Vcc of the KA22471, so either the board has problems in the power supply or the chip is shot and dragging down that voltage.
Hmm, well unfortunately I don't have a user's manual for it either.
At this point I'm not sure there's much else I can do without a schematic. Have only 0.2vdc at Vcc of the KA22471, so either the board has problems in the power supply or the chip is shot and dragging down that voltage.
Joined: Jan Thu 01, 1970 1:00 am Posts: 137 Location: Charlotte, NC
No, I haven't run it for long enough. Looked a bit around the board and found one diode in the power supply was cracked and faulty (not really burned though). Replaced that with a 1N4007, but didn't get a chance to measure voltages again (unit still only works on cassette).
I was very surprised to find that bad diode, I would have bet money that the whole PCB ran off one 5v supply. Does have 4 power diodes, I figured they were in a bridge configuration. Not sure where the KA22471 is getting its power from. Going to try and trace from that burned diode and see what it feeds...
Have you tried getting a datasheet for the IC online? I've looked up datasheets for ICs in some of my transistor radios just to find out more about how they work. I've noticed that some datasheets for ICs have sample application circuits as well as pin outs.
