Maxtrac Maratrac Power Control out of band

[eleet]

Hello kids.

Some of you have noticed that when running your maxtrac or maratrac out of band, the power and deviation control stops working or works randomly on some frequencies.

I have seen procedures to correct this by disconnecting the DAC from the radio and using pots. Well that's cool but I don't want to rework the radio. All the roms are in a socket so let's not break anything.

If you read the manual or played with RSS some you know the radio divides up its frequency range into 16 subranges. There is a table in the rom that helps the radio figure out which subrange we are in, to apply the power and deviation correction. This table has two values for each radio split, the beginning of the first range and the width of each range. When we try to tune above or below the frequencies the designers intended the power and deviation adjustments are looked up with an invalid index (0 or greater than 16 when they should be within 1..16) The same table is verbatim in each version of the maxtrac and maratrac rom I have examined.

For amateur use, 2m and 6m require correction to extend the 42-50 radio up to 54 and the 150-xxx radio down to 144. The 450-xxx radios already work fine down to 440.

Hunt for 20D0 006B in the rom to find the table. This is the first value to be changed (but not the beginning of the table)

Code: Select all

Changes:

OLD    NEW
20D0   20D0  42-50.56 5 kHz changed to 42-54
006B   0096

1A40   1A40  42-50.6 6.25 kHz changed to 42-54
0056   0078

....

07D0   0640  146-176 5kHz changed to 144-176
0177   0190

0640   0500  146-175.9 6.25 kHz changed to 144-176
012B   0140

Also the rom checksum should be changed too or the radio won't boot. I think all of you who have used hex workshop before can handle this.

OK, This hurts the radio a little but it will be fine in the amateur bands. If you are really picky you can calculate new center frequencies for the 16 sub-ranges and readjust the individual buckets yourself, but that will be a big pain.

I have been using the mods on VHF for a few months now and our ears and basic test equipment think that it works fine. I have an x9000 for 6 meters so I haven't personally been motivated to tune up one of these radios for that band.

[PETNRDX]

I have been meaning to reply about this but have been really busy.
It sure sounds like it should work, and work well.
I see you don't post all that often.
But when you do, it is a real Gem.
Not sure when I will get a chance to modify some PROMs and try this, but I am CERTAIN that I will.
Will be a much more elegant fix than the POT mod most of us have been using.

[KE7JFF]

I got a Maxtrac out in my car I use for APRS that has some interesting power control issues; I'll have to try this and see how it goes!

[SlimBob]

I've got a Maratrac I was hoping to use as an APRS digipeater; any idea on what sort of values of capacitors I should try distributing around the PA to get better efficiencies?

[ifr1600]

Hello kids.

Some of you have noticed that when running your maxtrac or maratrac out of band, the power and deviation control stops working or works randomly on some frequencies.

I have seen procedures to correct this by disconnecting the DAC from the radio and using pots. Well that's cool but I don't want to rework the radio. All the roms are in a socket so let's not break anything.

I would like to understand this a bit more. How do I navigate around the prom image knowing what to look at? I would like to modify the 900 maxtrac conventional software (FVN4019A) to a more ham friendly version. I also wanted to avoid doing these modes. let software do the work I say!

[SlimBob]

Buy or download books on the Motorola 68HC11 processor, and get a 68HC11 disassembler. Pull the PROM, read it, disassemble, and start matching things up.

The 68HC11 is unfortunately from a time before JTAG, and some processors contain "masked information". That means they have an internal EEPROM area or PROM area which isn't externally viewable. One would have to find a location the computer jumps to, feed it some instructions, and have it copy out the contents to a RAM buffer.

The 68HC11 has 1MB of address space, and certain things show up mapped into that space. The external EPROM jump/start location is FFFE+FFFF, but the internal is somewhere in the Bxxx+Bxxx range.