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  Replacing the Spectra MLM
By Alex Cobleigh K6LPG
Edited by Robert W. Meister WA1MIK
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I wanted to upgrade my 900 MHz Spectra from firmware version 2.09 (trunking) to version 6.14 (using an MLM from a high-power UHF radio). As I found out, it's not as simple as just swapping the MLM. I encountered multiple problems. After a lot of experimentation I discovered the hints and tips contained herein.

Things that you will need to replace the MLM:

If you can, use a remote front and don't hook a control head to it until you are ready to see if it will work. With the head connected to the radio, it goes into a continuous reset loop without any error message, but by removing the head this process stops. You can even have mismatching model and serial numbers with the head off and the radio will still continue to operate (as much as it can without a head).

Getting the Radio to Turn On Without a Control Head:

I have a special DB25-style programming cable with a jumper from pin 20 to pin 22, which connects the incoming A+ to the outgoing SWB+, a function normally performed by the control head. This will power up the radio without having a control head attached. Just plug this programming cable into the remote-mount jack on the front of the radio where the control head cable normally plugs in. For dash-mount radios, remove the control head and adapter board, and stuff a short piece of solid wire into the exposed command board socket between pins 30 and 31. Pin 32 is the keyway in the top row and is blocked off. Pins 30 and 31 are towards the center of the connector. Remove this piece of wire before you put the control head back when you're done with this procedure. See the photo below.


Note from WA1MIK:

You can also use this method to operate a radio without a control head, for use as a link receiver or transmitter. Just program it for the single mode you want.

The Saga:

I bit-banged the model number, head type, and frequency range (band) data into the command board. I also entered the proper serial number. These locations are documented in other articles on the web. After this, I attached the control head and the radio did nothing but continuously reset itself; no error codes were visible. I then unplugged the head, re-read the radio and checked it, and programmed it again. I reconnected the control head and saw no change.

Next I went into the Service Menu and to the Board Replacement procedure (F2, F6, F3, F2). I initialized the CPU (this takes a while) and continued with the alignment. Now I was able to read and immediately write the code plug to the radio to make the MLM and command board memory agree and fix the checksums. I entered a frequency and programmed that into the radio. I reconnected the head and it all worked now. In looking back over my experience, I think that initializing the CPU did the final trick.

Here are the contents of some of my radio's memory locations. Addresses and data are in hexadecimal format. [Editor's note: the data in the command board at B681 is what has become known as the Mo-Flags. These are documented on that "other" site. Also see the Spectra Hacks article elsewhere in this section for additional information.]

B68100Flags byte 0
B68276Flags byte 1
B68340Flags byte 2
B684A3Flags byte 3
B68519Flags byte 4
B686F7Flags byte 5
B687F1Flags byte 6
B688FFFlags byte 7
B68964Flags byte 8
B68A84Flags byte 9
B68B10Flags byte 10
B86C1FFlags byte 11
B68D11Flags byte 12
B69E00Flags byte 13
B69F00Flags byte 14
B69000Flags byte 15
605FEDControl head type
606067Frequency range

To change data in the MLM, you have to find where it's located. Usually it's after 6200. There must be a pointer elsewhere in memory that the computer uses to find it, but we humans have to do it the old fashioned way: by searching for it.

Contact Information:

The author can be contacted at: wac [ at ] att [ dot ] net.

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This article first posted 16-Jan-2010.

Article text © Copyright 2010 by Alex Cobleigh K6LPG.
Layout and hand-coded HTML © Copyright 2010 by Robert W. Meister WA1MIK.

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.