Re: Is my QCX 30 a write-off?

Alan G4ZFQ

Have attached an Excel sheet with all of my latest > readings (DVM).  Let me know if more needed.> Can't see any problems
around the processor & C47.
>Yes, I struggled a
bit with that sentence about the various processors. 8. Put P4 back in QCX 20 and still works OK
Hope that's more understandable.
Yes, the QCX30 is damaging the processors, as I'm sure you realised. The fault is carried through to a good QCX.
As far as I know this is only likely to happen if more than 5 V is applied, 5 V to the wrong pin or a short to ground on a critical pin.
There seems to be no actual list of expected voltages. (Maybe there is?)
I copy your results and looking at the schematic and manual add a few cross references.
The thing that stands out is pin 27, check again, maybe it's a typo?

(Dual purpose LCD reset /SDA expected 3.3 V I think maybe Hans has commented about this.) Yes,,,20,0,0,0::Created,,qcx+sda,20,2,0,28593804 in here, I'm confused now, pin 27 is pulsed briefly to 5V, is it normally pulled down? The voltage list in the manual says 5V.

Other than that I hope someone else can come up with a suggestion.

IC2 -1 4.6
IC2 -2 0 D4
IC2 -3 4.9 D5
IC2 -4 4.9 D6
IC2 -5 4.9 D7
IC2 -6 0 EN
IC2 -7 4.9 VCC
IC2 -8 0 GND
IC2 -9 0.42 XTAL
IC2 -10 0.45 XTAL
IC2 -11 1.01 TX=2.3
IC2 -12 4.85 ROTA
IC2 -13 4.85 ROTB
IC2 -14 4.84 TX= 0 RX
IC2 -15 1.76 TX=2.5
IC2 -16 0 TX=4.9 KEY_OUT
IC2 -17 0.34
IC2 -18 4.8
IC2 -19 4.8 TX=0
IC2 -20 4.9 AVCC
IC2 -21 4.9 AREF
IC2 -22 0 GND
IC2 -23 2.45
IC2 -24 2.44
IC2 -25 0
IC2 -26 0
IC2 -27 0 SDA/LCD RS ?5V?
IC2 -28 3.34 SCL

A quick look at other voltages, C43 looks suspicious leading to the low voltages following it. But maybe leave that until the processor is working..

73 Alan G4ZFQ

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