Which Spectra MLM?

[eleet]

I have some - possibly among the first ever made - Spectra D37's.

They all have this HLN6072B MLM with one 27c256 with "VER 1.01," a 28c16, and a 2k sram chip, along with some bypass caps and jumpers.

I'd like to have MLM's with 6.16 in them. Are there MLM's that use the old larger "hinge" connector in a configuration that will support this firmware set? Which model numbers are they? I'd like to simply exchange the ROMs and fix the EEPROM.

I'd like to get trunking and zones in these radios. Thanks.

[motorola_otaku]

Are there MLM's that use the old larger "hinge" connector in a configuration that will support this firmware set?

Negative. Gotta swap the MLM and command board with the more recent connector-type versions. You should also be aware that those old radios use a different RF/VCO board configuration as well and will not go into the 902 ham band with the resistor mod.. in fact, the VCO goes completely out of lock across the band if you install the resistor per the Repeater Builder instructions. And just to make it extra-useless you can't directly swap the VCO board with a more recent version because the RF board pulls its reference signal (or maybe sends the TX RF carrier, I don't have a manual handy) via a dedicated coax cable whose connector on the VCO board will not mate with a modern VCO board because the solder locations are different.

Basically, these radios are useless for 900 ham hobbyists except to maybe salvage a control head and a PA.

edit: I see you are looking to add trunking.. the one specimen of this vintage I have/had already supported it, afaik with at least 10 modes.

[eleet]

Thanks for the informative reply. I don't think the 1.01 firmware has any trunking support.

So, allow me to ask another question: What is the most capable version of the MLM that works on the old command board?

I did have a VHF Spectra many years ago, and I bought a new MLM from Ft. L. at the time. I had bought an A7 face to go on the A5 radio, it didn't work so I called, the tech told me I needed to change the model number and took my order for an MLM. Whatever came from Ft. L in '95 or '96 supported zones, so it must have been 6.something. However, I don't remember which command board that radio had. I may have the old parts around here somewhere, but there's no chance of me finding them anytime soon.

It may be possible to get the last firmware on an MLM and plug it in, however I don't know enough about the Spectra right now to determine the feasibility of this. I'll bet a dollar the addresses of the memory elements on either style of MLM are identical. The EEPROM on the command board definitely did not move. Even if the command board changed significantly, there may be a flag in one of the EEPROMs that allows the firmware to identify which platform he's running on.

[eleet]

Hm. I don't have manuals anymore, but Mike B's site has some info on the MLM pinout. The new rev has 3 more pins on the connector, one is used as a key and two of them are NC. It's likely that it's capable of holding and addressing all of the memories.

I think I'll be looking for MLM photos to find one that has the old connector and two 27c512's. I may be able to upgrade the MLM to handle all the larger memories by adding components and changing jumpers.

edit: found a photo of a command board with newer 40 pin connector for the MLM. All the custom "77M" numbered chips visible have the same numbers as on my older command board. Things are lining up.

[eleet]

I came across this stuff again and found out that the old command board has the A16 and A17 lines from the SLIC on the MLM connector.

The connector pinouts on either style of MLM pretty much line up. The three extra spaces on the new MLM connector are a NC pin 1, keying position, and "Load/Shift" connection to the cpu. On the old command board, the position intended for EEP2 select is permanently tied to 5v and not routed to the SLIC.

Apparently MLM boards with a 14-pin footprint for chip selecting logic do not handle the A17 line. If the board is packed with 2 32kbyte ROMs then it is still possible to select all memory without the A17 line. Despite this, it appears possible to rework these MLMs to handle two 64kbyte roms.