Micor LB Exciter - SP4

[Tim]

Hi folks,

Anybody have any information about a Micor Low Band Exciter
TLB8164A2 SP4?

It's out of a 10 channel mobile unit (extra channel element board across
back of unit).

Finally getting power out of it (several parts weren't populated), but
now I'm having a dickens of a time getting the audio to work right.

It had a PL board that didn't have all of the components on it - no
reed, etc.

Adjusting the IDC pot is quite touchy - not smooth at all.

The guy I got them from said that the control head had a PL
generator on it.

Anyhow, anybody have a clue (or would be willing to 'donate' a
'normal' exciter board for comparisons)?

Thanks,

Tim

[WB6NVH]

The Systems 90 accessory groups for these had the PL reeds inside the head for multiple PL encode, and there is then an adapter - interface board which goes where the typical PL board would be. I think this is covered in the Systems 90 manual and not the Micor manual itself. That is probably what you have, the adapter board, which is actually rather hard to find compared to the regular PL board.

The SP suffix is probably just for the extra channel element deck but anything is possible. The hardest thing to find is data on the -SP versions.

This was probably made in a reasonably small quantity, because anything over about 1000 units would have been assigned an "X" prefix for the radio itself and the boards, often a "YLB" prefix.

A perennial problem for me with Micors was dirty connections where the boards all plug together, fixed by spraying the connections with DeOxit cleaner.

[Tim]

Hi NVH,

Thanks for the info. The guy did say that the head had something to do with the multiple
PLs.

The exciter didn't have several resistors (which would make the channel elements play... they
must have been on the multi-freq board.

Have you ever heard of them using a different audio chip in the modulator? Was just wondering,
as the audio issues are pretty wierd. I've been all over the board & it now 'looks' stock, but
the IDC pot doesn't respond smoothly.

Back to digging... thanks again for the info.

Tim

[Tim]

Well, it's partially resolved...

The IDC pot was open, thus the 'wierdness' when turning it. So
the main audio works good now.

The PL tone coming from the PL board is right on spec - about 225 mvAC
with my 100.0 reed in. However, with the combos of the resistors they
had (5.6k paralleled with 3.9k) resulted in about 7kHz deviation!

I had to put about 75k ohms series resistance to make it work. Clearly,
this isn't right, so will continue to look. All the parts look like they are
there & correct value.

Tim