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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 23rd Mar 2023, 12:34 pm   #1
ex seismic
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Default Fm914pm

This is a Mould unit. Control head, PA and speaker all mounted on panel with a holder for a phone/handset, and all connected up.

My initial question is what supply, 12 or 24 volts? I have tried 12v and it is dead. I am wary of putting 24 v on it in case I am missing something. If I can get it to switch on then maybe there will be questions about re-programming it.
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Old 23rd Mar 2023, 1:17 pm   #2
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Default Re: Fm914pm

Long time since one of these turned up!

No 24V version as far as I know. It would need an external converter. Don't try it!

I suspect that power up needs EPROM to be fitted for uP. That would contain frequency info.
Maybe it has been removed for security reasons before disposal.

The main board is under the long cover. PCB underneath hinges out and presence or otherwise of EPROM will be easy to see.

Last edited by Jon_G4MDC; 23rd Mar 2023 at 1:22 pm.
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Old 23rd Mar 2023, 4:07 pm   #3
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Default Re: Fm914pm

Thanks Jon. I will take it apart sometime soon and have a look inside. It is quite possible the EPROM has been removed, from the same source we have a Cougar set which has been gutted.
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Old 23rd Mar 2023, 4:53 pm   #4
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Default Re: Fm914pm

I like the 900 series. I had them for 4m 2m and 70cm.

I was part way into making a 6m one. I got the synthesiser done but the helical resonator front end defeated me. The modules are made with ceramic thick films soldered to a metal frame (without encapsulation just a tin plate cover).
Probably a blow lamp job to work on them and I chickened out.

I might still have the guts of it somewhere. I suppose your one is Low Band ~4m?

Last edited by Jon_G4MDC; 23rd Mar 2023 at 4:59 pm.
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Old 23rd Mar 2023, 6:07 pm   #5
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Default Re: Fm914pm

Being ex Mould I guess it is low band. Nothing on it to indicate which band it is though.
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Old 23rd Mar 2023, 8:07 pm   #6
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Default Re: Fm914pm

The only post 1970s mobile that was built with a 24v option was the W30AM boot mount 30W Westminster. Can't recall any others.
After then, as Jon said, external 24/12 converters were used.
VC290 or VR200, the A200 linear amp box lookalike.
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Old 23rd Mar 2023, 10:23 pm   #7
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Default Re: Fm914pm

I forgot those. W30AM bus/coach version.
Premier travel probably had quite a few to bring the workers in from the fens.
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Old 24th Mar 2023, 9:19 am   #8
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Default Re: Fm914pm

I just thought it might have been 24v being ex military. I can report that there does not seem to be anything missing in either unit. Two what I take to be EPROMs on the control board and something the same size in the head unit. I'll add it to me round tuit pile.
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Old 24th Mar 2023, 10:07 am   #9
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Default Re: Fm914pm

Interesting...don't remember 2x EPROMs but it has been a very long time.

I have a zip file which is supposed to be a scan of the manual. It seems to be full of .TIF files which wouldn't open on a first cursory try. Now I have properly unzipped it the results look very promising. Not got as far as circuits yet but the variants table is just as I remember it.

Somewhere in the shed is also an FM91 manual in hard copy.

Power supply spec 13.8V Negative Earth. No mention of 24V DC option.

Last edited by Jon_G4MDC; 24th Mar 2023 at 10:18 am.
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Old 24th Mar 2023, 2:03 pm   #10
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Default Re: Fm914pm

The FM 914 ex Mould have only had 1 EPROM fitted in the transceiver unit
from memory a 27c64 on the Synth & Control board.
The Mould set's where low band 68 -88 mHz 12 volt.
There may have been a 24 volt to 12 volt dropper for the use of the FM 914
in military vehicle applications

Paul G8YLB
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Old 24th Mar 2023, 2:49 pm   #11
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Default Re: Fm914pm

Thanks for info about EPROM.

I have also found a note which says the EPROM checksum is continually checked. If an error is found it switches off and can't be switched on again until the faulty EPROM has been replaced. It will also switch off if the comms fail with the control head.

Of course there can be lots of other reasons it won't power up.
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Old 31st Mar 2023, 10:46 am   #12
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Default Re: Fm914pm

While looking in one of the computing threads I found mention of the Epson HX20 - just about the world's first laptop.

There was an FM900 portable programming workstation based on that.
A custom made EPROM programmer was mounted to the left hand side where the paper rolls are seen below.

It had a pair EPROM holders, one for the Master EPROM chosen to suit the FM900 variant in question - matched to the Hardware Code. The second slot held the blank target EPROM which was going to be written to suit customer channels and frequencies.

Do any of these survive I wonder? The one I knew of died from NiCad electrolyte leakage eating the PCB.
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Old 31st Mar 2023, 4:17 pm   #13
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Default Re: Fm914pm

Have not seen anything like that before Jon
We had a 386 or was it a 486 desk PC with a Stag EPROM card fitted to burn a Prom
after generating a file from the FM 900 programming software.
It also had a a CDP card fitted for FM 1000 programming.

Paul
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