Maxtrac channel memory capacitor

[atlantis]

Hi

I once knew where to add a supercap inside the Maxtrac to make it remember the last used channel for a longer time than it does normally, just for the case of a power failure. I even bought the caps then but haven't installed them since and now I can't find the info anymore. Can anyone help please?

73
Martin

[jackhackett]

Do you have the radio model number or better yet the logic board part number?

[jackhackett]

Also this is in the wrong forum section, should be in 'legacy radio discussion', maybe we can have an admin move it?

[train_radio_guy]

Perhaps I missed something. Is this not the "General Motorola Solutions & Legacy Radio Discussion"?

I wish I still had my 'thick' service manual for the Maxtrac Radio Series. IIRC there was an addendum from Motorola, which made reference to the 'supercap'. Sadly, I did not have the foresight to make a copy of it, back in the mid-1990's. If I find someone who has a copy of it, I'll be sure to let you know.

[jackhackett]

Perhaps I missed something. Is this not the "General Motorola Solutions & Legacy Radio Discussion"?

Yes, you missed the topic being moved, it was originally in the 'base stations, repeaters, general infrastructure' section.

I believe the cap would go in the "RAM 5V" circuit that feeds pin 2 of the microprocessor, there's usually a 47uF cap in there, not sure of you just replace that with the super cap or if there's something else involved.
I might have that addendum, I'll have to look around for it.

[train_radio_guy]

My mistake. Sorry about that jackhackett.

[jackhackett]

I know this topic is a little old, but I was just looking at the GM300 manual and it shows a revision with a 4V battery and diode connected to that 47uF cap. You can see it at the repeater builder site, gm300 service manual part A.

[train_radio_guy]

Yup. On page 9 of the pdf - B401, 4 volt battery. The schematic diagram indicates it was optional. I'm trying to remember if I ever saw one installed. Perhaps, for one of the early ESDA Communication Vans, used by a nearby county. I think they eventually upgraded to a Spectra, for more channel capacity.

[RFguy]

I recall doing this many. many years ago. just dug out an old manual and it shows the mod. It was just as jackhackett said, the 5VRAM line that feeds pin 2 of the of the SLIC logic array.

We added a lithium battery through a signal diode (probably a 1N914 or 1N4148). Battery negative to ground, Batty + to the diode Anode. Diode cathode (line) to the + side of the radios C408 (47 uf cap).

In this case, the logic board was a HLN9313, but should apply to other boards too.