Easy!

[N8YX]

Per the "Let's make this a 'radio' site" thread by 'IEI:

Ever find yourself staring down at what looks to be a long and expen$ive rig-troubleshooting process...then find out that the symptoms are caused by something extraordinarily simple?

I'll go first -

Last evening I was getting ready to join our area 10M net when I hit the '940's "Autotune" button...zip, zero, NADA. No RF at all. Looking at the VC and IC meters, one sees around 28v and ~10A. The ALC meter showed full scale with no drive.

Shorted finals ??!!?? Wholly FSK! :shock: Them's $232 a set plus installation and aggravation charges!

I opened the case, disconnected the PA's 28V supply lead and repeated the test. Still reading ~28V and ~10A...with no final transistors connected!. The ALC meter now showed zero.

Something's not right in the metering circuit.

Checking the service manual, one sees that the Control Board handles metering, AT control and a myriad of other functions - including high SWR power foldback and ALC.

Deeper we dig...Connector #10 interfaces the AVR (28V board) to the Control Unit. VR10 sets the IC '0' point and VR11 sets the 28V reading.

Now if said connector is flaky...or the pots are intermittent...then the rig "assumes" it's in a fault state and will not transmit because of the (erroneously) high IC/ALC readings!

Resetting Connector #10 then adjusting the two trim pots got the rig back to full output.

[W5IEI]

I have one.
A while ago my AL-1500 started acting flaky.
The HV would fluctuate 3-500 volts,and I could hear the windings buzz a little.
I took the cover off(after letting it set unplugged for 24 hours)and tightened everything,looked for burn marks,etc.
Still,I had a problem!!!!

Went outside to unplug it again(yes my 240 plug is outside)and saw telltale signs of fireants around the pole.
I disconnected everything,and took my 240 socket apart,guess what?

Yup,full of fire ants!!!!
Cleaned everything out,problem solved :D

Look at the easy stuff first.
Mike

[WØTKX]

The problem is, the easy stuff can be hard to find.

[N8YX]

The problem is, the easy stuff can be hard to find.

But Wait! There's More!

I spent almost all day running down the assorted loose connectors, blown bulbs and oxidized/out-of-adjustment potentiometers in the '940. Still have an ATU problem; it doesn't tune when you hit the 'Tune' switch - and I guess the S-meter could use a bit more adjustment - and one of the RF ATT relays appears to be dirty...but we're getting closer.

[KG4CGC]

Sounds juicy!

[N4VGB]

How about one month spent running down a mystery noise on the output of a Heathkit Apache TX-1, that I'd already gone through completely and refurbed!!! :twisted:

I went through that thing with a microscope when I refurbed it, all functioned perfectly when completed, except for this very strange noise on the output that I could hear on a rcvr and see on the scope???

To make a very long story shorter, after stripping it down to only the bare crystal oscillator and VFO circuits, the noise was still there on both??? Hmmmmm? :chin:

A month later the source of the noise was discovered to be a battery float charger that I had "temporarily" put under the workbench and forgotten about. The noise was a feedback into the AC outlets on my whole workbench!

[KC2UGV]

How about one month spent running down a mystery noise on the output of a Heathkit Apache TX-1, that I'd already gone through completely and refurbed!!! :twisted:

I went through that thing with a microscope when I refurbed it, all functioned perfectly when completed, except for this very strange noise on the output that I could hear on a rcvr and see on the scope???

To make a very long story shorter, after stripping it down to only the bare crystal oscillator and VFO circuits, the noise was still there on both??? Hmmmmm? :chin:

A month later the source of the noise was discovered to be a battery float charger that I had "temporarily" put under the workbench and forgotten about. The noise was a feedback into the AC outlets on my whole workbench!

Ok, that's one of those things that's seen as funny as long as it aint you :)

[w2amr]

When I first got my Johnson 500, I fired it up on the bench , and loaded it into a dummy load. At first everything was fine. Then it started popping the HV fuse ever second or third time I turned the HV on. I could hear an arc snap when it did it, but I couldn't see where it was coming from. So I turned out all the lights in the room, hit the HV switch, and saw a spark at the rear apron of the RF deck, around the HV feed throughs. Sure enough, I took them apart and found one was cracked, and there was a carbon track to ground .I replaced the feed through, and all seemed fine. I put everything back together and hauled the modulator/PS and rf deck back into the shack and hooked it up. The transmitter worked fine for several days, then started the same schitt. I brought it back to the bench in the garage and went over every square inch of the HV P/S ,but I couldn't find anything wrong. In desperation I installed 2 new mercury vapor rectifier tubes, and it still blew fuses. Then a friend suggested I replace the Mercury vapor rectifiers with K2AW diode stacks, which I did. The transmitter has never blown another fuse. One of the great unsolved mysteries of our time. :wall

[N8YX]

I ran into a similar scenario when I was repairing an old Tram Titan II for a guy...he'd cranked the power output up to the point that it heated and carbonized an insulating wafer in the T/R relay. Of course, said segment insulated the B+ wiper, which engaged and applied voltage to the PA tube plate when the PTT swtich was activated. Upon key-up, however, the effect was akin to shorting the B+ supply to ground through a low-value resistor...which is exactly what the carbonized phenolic wafer had become. Immediately blew the supply fuse - every time.

Fixing the problem was fairly easy, even if it did involved "building" a new relay with pieces of the old one. Finding it was another matter entirely, as there was nothing on the outside of the relay which indicated it was bad. It took a couple of days.

[N4VGB]

In desperation I installed 2 new mercury vapor rectifier tubes, and it still blew fuses. Then a friend suggested I replace the Mercury vapor rectifiers with K2AW diode stacks, which I did. The transmitter has never blown another fuse. One of the great unsolved mysteries of our time. :wall

Shame on you George. 3B28s would have retained that classic look and cured the problem.