TMC SSB Adapter blows breakers, but not on Variac!

[WBear2GCR]

So, here's an odd tale.

That nice TMC SSB Adapter in my post on the rack, when in the rack pops the breaker
in the outlet strip. It's the TMC MSR-4, but it has another nomenclature that the unit is more often
found as...btw.

Anyhow, I thought this rather odd. It worked fine on the bench, connected to the Variac (tm General Radio).
Brought it back to the bench, worked fine. I thought, hmmm, the inductance of the variac is absorbing
the turn on rush! But, that did not make any sense, since I didn't see that much current draw on
turn on watching the AC Ammeter (that everyone has) connected to the load side of the variac.

Someone on-the-air suggested replacing the outlet strip. Which, I suppose made sense, and I did. No go.
I also grabbed an iso transformer on the theory that it was an inrush current thing. BUT...

Anyone figure it out yet?

I did, a few hours ago.

The chassis was HOT!!
Yep 118vac right there...
Plugged into the GROUNDED outlet strip - BAMM!
Plugged into the ungrounded Variac? Nothing...
Good thing not much around the bench IS grounded - this from many years of working on stuff.

Ok - so what was doing it?
Leaky AC mains input caps?
Bad power cord?
Shorted power transformer? (whooo, really hope it's not THAT!)
What??

Long story short, this is a TMC unit, laced up wiring harness and all. The unit only dumped
AC mains onto the chassis when the power switch was on. So that left everything after the
power switch. No choice but to trace the wires from the power switch out, and start disconnecting
wires until the ZERO OHMs to ground went away or was found.

The pictures below show what i discovered!
Did this come from the factory like this??
Or did someone go in there to "fix" something??

Look closely at the picture with the little mirror. Can you see it?
Hint: the leaf that is closest to the mirror carries the AC mains coil activating
voltage! See it yet? What's in the picture is NG.

The other pix is the relay itself.
The reason they went with the relay and not a wafer switch is that they needed (for what
I do not know) to be able to remote the USB/LSB function. This setup permitted a single momentary
button switch to toggle between upper and lower.

So, the lesson here is that one should never assume that anything is automatically
wired right and free of defects. Let the trouble shooting lead to exactly what it is...

An odd tale.

[WBear2GCR]

Anybody spot the problem??

It's in the picture in the mirror!


    _-_-

[K4NYW]

And a warning - the 3-wire MS connector on earlier CV-591A (TMC MSR)
is wired differently from those on later ones and most other
military gear I have come across! The standard is ground on pin B, but
TMC didn't do it that way on early CV-591A for some reason.

TMC wired early MSR’s with pin C ground and later ones with pin C hot.  Be Careful!

I think the SRR-13 series of Navy receivers also had pin C ground, but don't trust me - use your ohmmeter!!

Making physically-interchangeable power cords with different pinouts is criminally stupid in my book.

[WBear2GCR]

This one, fyi, has a hardwired power cord, it's got a square plate at the inlet with a grommet.
It's got two screws on opposite corners, and pop rivets on the other two! The power cord
goes in the grommet and has a knot on the inside as a strain relief.

Flipping the hot/neutral, not good practice.

It's scheduled for replacement... probably an IEC. Non-mil as it may be.


But Nick, did you spot the fault??

              _-_-bear

[Opcom]

The leaf in question has no insulator between it and the frame. Can you find or make one for that? Time to dig out the box of old nasty relays you would never use but have hesitated to pitch out. Is this correct?

[WBear2GCR]

The leaf in question has no insulator between it and the frame. Can you find or make one for that? Time to dig out the box of old nasty relays you would never use but have hesitated to pitch out. Is this correct?

BINGO!

Give that man a prize!
Sharp eyes + experience there, folks...

Exactly so. Turns out the dark one just above the leaf belongsbetween it and the frame!
That's how it is on the other side.

Now who did it that way, why, or if it was a relay factory error?
Dunno.

The interesting part is that in some strange way I have some sort of "vision" in troubleshooting.
When I looked at the schematic, my eyes "rested upon" that relay coil!

Somehow this happens to me all the time - I just focus for no apparent reason on an area of
a piece of gear, or part of a schematic - and then spend hours troubleshooting, testing, eliminating
things, only to end up exactly in that spot.

Like when I went down to my other QTH, my eyes rested upon a right angle screwdriver.
I looked at it, picked it up, and thought to myself "should I take this with me"?
To which I thought, "nah, I don't NEED it up there..."
Put it back down.

Guess what?

To undo a barrier strip that had the exact wire that ran to that relay, necessary
to remove the spade lug in order to troubleshoot that very run, there was no room for
a standard screwdriver!! (brilliant placement by the design team...)

So, a few hours later, guess what? Yep I needed it.

Had to "fake it" to move those screws on the barrier strip...

Happens to me all the time!!

                    _-_-

[Opcom]

In the old days we had an old tube TV set, that, once it was on for about 15 minutes, would occasionally do the veritcal roll for 4 or 5 minutes then lock back in and be fine for the rest of the evening.

I got called from my room every time anything went wrong with the TV because by then I was the one fixing the TVs and radios at home.

My younger brothers thought I was 'staring it down" and more than once a couple of their friends would conveniently be over, just to see this magic.

This was back in the days when the TV and radio were magic and the TV repairman was a properly revered figure.