Specs for the tuner pot on the first LCRU boards

Your best bet is to find someone with an old R2LC and scavenge one from there.  Check with Marty Fitzhenry, he used to have some old boards, maybe he can get one of these for you.

That's a variable trimmer coil.  If you can pick off any numbers stamped on the can, look for the digits 8128.  For the Motorola radio chips used in TMCC boards, a popular coil was the Toko 7MC-8128Z which is about 7mm on a side.  But good luck finding these today - GRJ's scavenge approach is the way to go!

I've tossed bad R2LC boards in the past with these, never thought I'd need them.  If I still had one, I'd send it to him.  I may yet have one soon, I'm working on some old locomotives with LCRU boards, and I know at least one of them is dead.

So you got me thinking.  Now that I re-read the OP, it's not clear TRW wants a replacement part for a board gone bad.  Perhaps TRW is just trying to learn more about how quadrature coils are spec'd to demodulate FSK modulation? 

Hey, GRJ, maybe your LCRU boards are bad because of a broken trimmer coil!

That would be his bad luck.

LOL.  BTW, can you read any numbers off that coil coil?

4375 stamped ink on an older R2LC, not sure if that crosses to anything.  I have found LCRU can be repairable.  Usually a blown diode or VR shot.

If the fixed one has a part number and your looking at a repair won't that work, vice getting the obsolete style?  G

The same thing is on the LCRU I have here, it's in a square on one side.

4  4

7  5

Very odd way to number things.

That must be a part number of some kind.  Of course, I'm not sure why this particular part would go bad.

Guys,

Thanks for all the help. I'll try the transplant method from a dead R2LC when I find one in a junk box around here.

The weird thing is that the tuner pots on the old LCRUs are shrink-wrapped whereas the ones on the R2LCs aren't. It could be nothing, but I'm wondering if the specs changed between the board revisions. Only one way to find out...

Regards,

TRW

I have not looked closely, but I wonder if the fixed version has the same board footprint. I do have a R2LC that burned the PCB at the smoke TRIAC.

What I have found from research is the radio chip sensitivity can be effected by voltage spikes and issues with some of the capacitors and resistors attached to the various inputs and outputs of the radio chip.  Apparently this chip was used in RC helicopters.  I found the information on one of the RC helicopter forums years ago.  G

I don't think the tuning coil changed for the life of the design.  Starting with the R2LC versions around the C08 firmware timeframe, the tuning coil was removed for what appears to be a ceramic filter for frequency control.