Re: Wacky voltage readings


Clint Sharp <cjaysharp@...>
 

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=yahoo.com@groups.io> 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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