Up one level (Spectra index) Up two levels (Moto index) Back to Home

Replacing the Spectra MLM By Alex Cobleigh K6LPG Edited by Robert W. Meister WA1MIK

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:

• Spectra lab software.
• Modified DB25-style programming cable (see text below).
• 12VDC power supply.
• Remote front cover with 1 or 2 DB25F connectors on it.
• Lots of coffee.

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.]

Addr	Data	Function/Use
B681	00	Flags byte 0
B682	76	Flags byte 1
B683	40	Flags byte 2
B684	A3	Flags byte 3
B685	19	Flags byte 4
B686	F7	Flags byte 5
B687	F1	Flags byte 6
B688	FF	Flags byte 7
B689	64	Flags byte 8
B68A	84	Flags byte 9
B68B	10	Flags byte 10
B86C	1F	Flags byte 11
B68D	11	Flags byte 12
B69E	00	Flags byte 13
B69F	00	Flags byte 14
B690	00	Flags byte 15
B691	80	Checksum
B692	13	Checksum
605F	ED	Control head type
6060	67	Frequency 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.

Back to the top of the page
Up one level (Spectra index)
Up two levels (Moto index)
Back to Home

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.