Maratrac problem

[kf4sqb]

I've encountered a VHF high-band Maratrac with an A7 head that has developed a strange problem after being stored for a while. The radio was working when last used, app. 3.5-4 years ago, and has been laying unused (in a sheltered environment), since. Hooked the radio up and tried to power it up today, and hit problems right off. When first powered up, the control head remains dark, and a repeating series of three loud beeps comes from the speaker. This continues for app. 30-45 seconds, then the head finally lights and everything appears normal. However, the buttons on the head don't function. I thought that maybe reloading the codeplug would help, so I reloaded a saved codeplug. Initially, this seemed to solve the problem. After reprogramming, but before powering the radio off and back on, everything works normally, but goes back to the same thing after cycling power. The radio also won't key up with the PTT while in this condition, but will key up via the RSS. I thought that maybe this was a capacitor issue, like with a Spectra, but don't see any sign of leakage in the control head. Any ideas?

[jackhackett]

Open it up and find the logic board, look in the shielded section of the board, is there a black Dallas Semiconductor module?

Early maxtracs, and I would guess maratracs as well, used a NOVRAM instead of the later EEPROM. The NOVRAM is basically a static ram chip with a lithium battery built in. The battery has a lifespan of 10 years or so, when it goes dead the chip will no longer retain it's memory. This could explain why it worked after programming until you powered it off.

[kf4sqb]

Intriguing possibility. I'll check that out, but I kinda' doubt that's the problem, as I read the radio before reloading the codeplug, and all the data appeared intact. I'll still check it out, though.

[kf4sqb]

Jack, you are correct in assuming the early Maratrac used the Dallas chip like the early Maxtrac. The unit in question does indeed have a Dallas chip in it. Do you know of any way to check the internal battery? I don't see any way from the chip's datasheet. It almost certainly does have at least 10 years of idle time on the chip, though, so I'm going to have to say that the battery in the chip is probably dead. I'm supposing (hoping!) that all I need to do is replace the chip with a new one, and dump in an archived codeplug? Thanks for the suggestion!


Oh, one other question, do you know the timing of the original part? Its not listed on the chip, and there are at least two different timings available (150ms and 200ms, IIRC).

[jackhackett]

There are a number of posts on the board about this, here's one that reports it can be replaced with a 28C16 EEPROM

If in doubt about timing you can usually go with the faster one (lower number).

http://batboard.batlabs.com/viewtopic.p ... om#p147369

[kf4sqb]

Thanks, Jack. I think I have a few 2816 EEPROM's floating around here. I may try replacing it with one of those.