Re: Wacky voltage readings
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Sounds likely, IC4 is a nice large SMD so it¡¯s easy to remove and replace with nothing more than a soldering Iron and care. If you¡¯ve a pin chuck and a sewing needle you can put them to good use in the process?
On Fri, 13 Jul 2018 at 03:30, Charles W. Powell via Groups.Io <doctorcwp= [email protected]> wrote: Alan (G4ZFQ),
I did more pondering on the QCX I am trying to repair and did some experimenting.? I removed the transformer leads that go to pins 7 and 9, and I now get an expected voltage division between R1 and R2 at 2 volts. Shy of the published voltage but exactly half of what is supplied to R2. Regulator output is 5.01 volts but I¡¯m still getting exactly 4 volts at R2 - not sure why.? The LCD seems to operate just fine.? There is obviously a trace or a bus that spans the board but wow! Trying to find that is going to be tough.
With T1, C45, and R9 fully removed, I no longer get high voltages on the ICs, 5, 6, 7, etc.? Rather the voltage that were ridiculously high drop down to about 0.5 to 1.5 volts in most instances.? I no longer have 11 volts anywhere on the IC pins.? Even with C45 and R9 removed, pins 5 and 12 on IC4 still show nearly a dead short to ground (about 10 ohms in the path). If there is a solder bridge somewhere, it¡¯s beyond my capability to see it.? I am beginning to think strongly that IC4 has at least a bad segment in it.? Some of it must be working or the radio wouldn¡¯t receive anything.
At this point in time, I am supposing that there is very little to lose by trying to replace IC4, surface mount be damned.
Thanks for your help with trying to track things down, Alan.? I¡¯m open for more suggestions (from anyone!) if they are out there.? Since it would be ridiculous to try to remount T1 with the existing wiring, I will re-wind the transformer.? Then I can be certain it is mounted correctly.
73,
Charles - NK8O
-- Clint. M0UAW IO83
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