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[bkenobi]

I'll take a look tonight to confirm the model number.  It looks just like 61-2677B based on the images on google.

The meter is a pretty nice digital Craftsman unit with a thermocouple and serial connector.  I doubt it's as good as a Fluke, but it's done everything I've asked of it to date (other than measure capacitance of 1000uF).  I think it's this one but I'll confirm tonight (Craftsman 82357):

http://tinyurl.com/j8ajgfe

[bkenobi]

Oh, and I never thought about it but perhaps it could be useful information.  The red LED does not light up when transmitting anymore.

[Brian H]

OK I will look at the prints I have. For the MC460
I may have been confused. As your thread title says 61-26778

[bkenobi]

Yeah, I'm sure it's a "B" not an "8" at this point based on pictures that I've found online (and the fact that I can't find anything for "8").  The controller is a little dusty from sitting in the shop for years so it's not that easy to read which is most likely why I wrote down the wrong number.

[bkenobi]

I can confirm that the correct model number is 6-2677B.  The DMM model number is 82357.

Also, I was wrong about the LED.  It does illuminate during PLC transmission as it should.

[dhouston]

...it's not that easy to read which is most likely why I wrote down the wrong number.

It's probably a common problem as most online listings use 61-2677b, likely to avoid confusion.

[Brian H]

Thanks for the updates.
I will look at the MC460 schematics as I have seen some references to it from a RS part number.
The Red LED working is a good thing. It is driven from a controller chip output pin through a resister. If it was out. May have indicated a bad controller or LED itself.

[Brian H]

There isn't much left in the power line transmitter circuit. If it matches the MC-460.
There is are two resistors on the Base. R8 4.7K to the controller chip and R7 1.5K to common ground.
Emitter R6 10 Ohms to common ground.
D6 68 volt zener diode from the Collector to ground.
T1 coupling and oscillator transformer for the 120KHz power line signal.
C3 {.22K smaller of the two Mylar Caps} couples the 120KHz to the power line.

[dhouston]

D6 68 volt zener diode from the Collector to ground.

D1 gets my vote.

[bkenobi]

Aren't D1 and D2 the diodes I originally replaced?  One of them was 18V.

[dhouston]

Aren't D1 and D2 the diodes I originally replaced?  One of them was 18V.

OK - I didn't recall you mentioning replacing any zeners.

[Brian H]

D1 and D2 are in the power supply. They are most likely the ones you changed. D1 is the 18 volt zener.

D6 is in the power line transmitter and is 68 volts. If it is turning on at too low a voltage. It may lower the transmitted signal.

[bkenobi]

Which one is that?  I can pull it and test it to see if it's working.  Or, according to Google, I can just measure the voltage across it to verify it's correct (68v I assume).

[Brian H]

It is used to suppress high voltage spikes from the transmit transformer. When the power line transmitter is sending data.
It is connected to the same PCB run as the collector of the transistor.
It will have 18 volts on it through the windings of the transformer when not sending any commands.
Check the 10 Ohm resistor on the emitter. Along with the 1.5k and 4.7K resistors on the base.
Though they are not prone to failure. The .22K blue Mylar capacitor may also be bad. It puts the X10 command on the power lines.

[Brian H]

One big point. It has a power line derived power supply.
The 120 volt line connection is on some of the PCB runs and power supply voltages.
So extreme caution has to be used. Anytime a live readings are being taken.
A line voltage isolation transformer is best to be used but not usually in most users equipment list.