Re: Wacky voltage readings

Charles W. Powell

First, all ICs are in the correct orientation, so that’s not it. I will save the voltage issue on R2 for further investigation.

Checking C43-46, I found that C45 faults to ground on both sides. I removed it to see if the problem was the capacitor, and it made no difference.I’m assuming that since C43-46 have identical function, that this is related to the problem. I have not yet found where the source of this fault to ground might be. Although the soldering around IC5 and surrounding parts is not as pretty as I like to see it (NOT MY BUILD!) I can’t find anything shorted to ground - yet. Of course that’s complicated by the fact that C45 is connected to R9, making it hard to isolate R9 for testing. R9 has a resistance to ground of slightly less than 10 ohms on one side, and 110 ohms on the other. The other three similar resistors have 500K or more to ground. So, presumably something in the chain from pins 5 & 12 of Q4, or the path between C45 and R9 is grounded. I guess I’ll have to keep looking.

Also, current drain idling is about 117 ma at 12.8 volts on the bus. I’m finished with live testing now, because I will need to replace C45. It didn’t survive surgery.

Again, thanks for your help, Alan.


Charles - NK8O

On Jul 11, 2018, at 4:00 PM, Alan G4ZFQ <> wrote:

I show 19.91K from R2 to ground, and 9.96K for R1 plus 9.95K for R2.
C6 shows resistance across it of 9.96K, which it should since it parallels R1, so I do not identify a problem there. I get 3.98V at R2 on one side,


I get 3.98V at R2 on one side,
It should be 5V on one end. What current is the CQX taking?
Looks like the centre of R1/2 is going to ground when IC4 is switching.
Check for shorts to ground on C43-C46 and the associated pins of IC4.

and nominally 0.15 volts on the other side. That is also what I show +/- 0.05V at the four points on T1 which is quite low for the published specification of ~2.36V. And I still have the following on IC-5, way out of spec:
Is it possible IC-4 is fried and that’s where the voltages or lack there of originate?
It is possible but more likely is a solder bridge.
Again, it is possible one of the capacitors is faulty.
Are the ICs correctly oriented?

73 Alan G4ZFQ

Join to automatically receive all group messages.