MX300-S more channels on switch?

[KA1AXY]

My ham club recently received a donation of some H43SSU3140AN MX340 portables. Assuming we can get the code plugs reprogrammed at a reasonable cost, and of course, new batteries, they could be useful!

I'm curious if anyone knows whether the channel switch can be unblocked to allow rotation to 12 positions instead of the current 4? I did it once on another commercial radio, wonder if it's possible on MX300s without replacing the switch? I think it was a Grayhill switch, and you had to unmount it and pull a pin out to enable rotation.

[wazzzzzzzzup]

hi, i too have a mx that is set to 8 channels, it is capable of 12. i have looked at the switch and yes there are pins, but.... the pins are recessed with nothing to grab on to, so i am out of ideas. would be interested in finding a way, other than replacing the switch. good radios, you will need to do some configuring of them, possibly to get them to work for ham, it can be done tho. you will want to make sure the PRESELECTOR labeled "PRESEL" in the radio is a 71A2, that is the 136-150 setup.
i have more info if you ask, addl questions.

[bernie]

My two bits worth:
The code plug has 4 zones, 12 channels each.
The 12 channel model defaults to zone 2.
The flex circuit has provisions far a zone switch.
By adding this switch you get 4 times as many channels
as you already have.
If you have the older code plug which is not reprogrammable, you could jumper. the flex to another zone.

[KA1AXY]

Thanks to both of you. I understand about the plug not being reprogrammable. What I meant was what you suspected, use another zone & rejumper, which I gather is the "standard trick". The space where the zone switch goes on the top panel is inhabited by a noise squelch adjustment knob, which I think I'd rather leave there.

The pins in the switch sound very much like a Grayhill switch. They're visible
when you look down the shaft, after you've removed the switch from its mounting? They should just shake out. At least, they did on the one I modified years ago. Maybe the mfr got cheaper & made them "push in once only" into a plastic body or such.

Anyway, thanks for the tips, and especially the one about checking for the 71A2 preselector! Didn't want to start mucking about in the radio until I had a hint of whether what I wanted to do was possible.

I'll post about how it all turns out,
Peter

[Tom in D.C.]

Peter:

Later versions of that plug-in EPROM are reprogrammable, so you could just replace the existing "one time use" units with reprogrommable units and not have to mess with the flex (bad idea) or the switch (messy work).

Tom, W2NJS
...in D.C.

[dfc2]

Yes, you can remove the pin.....takes a few minutes per radio. This is what you do. remove the front of the radio, remove the knob, remove the nut holding the channel selestor into the radio frame. you will be able to get the switch about 1/2 inch away from the radio. remove the rubber washer (Mine were orange) and using a dental pic, start scraping around the outside edge of the pin, what your doing is scraping away the film used to hold them in, takes a few minutes and you will see that the pin gets loose when the coating is scraped away, and the pin will fall out. I don't recall which pin it is, there should be 2 pins, one to stop the selector at the proper channel, the other to stop it from going all the way around..it should not be too hard to figure out which one to remove.

any questions, PM me.

DFC2

[wazzzzzzzzup]

as for programming a new zone in a blank zone of an old prom, i have been tols personally that often times the old prom wont program right if at all on the blank zone. i bought and had programmed a "C" revision eeprom, it was made in 1989, wich tells me that motorola prob started using eeproms for replacements of older proms areound 1989 or later.

another thing to look for is if you have a recieve filter or a RF preamp. both can plug into one slot, so you have one or the other, if you can find it in your radio, and you have an RF preamp that is good. i think the matching preamp to the 71A2 preselector is a 61a i have seen several part numbers, for various bands, think they are something like 61a 62a 63a
anyway, if your radios are currently up in the 150-170 range, you will need to retune the VCO coil down a bit but do this only after you have replaced the preselector to your ham range. 71A2 and also have your eeprom installed with all your ham freqs. (im personally glad i didnot have to pay someone big bux to tune this, because it was fairly easy and i am pleased with the results that i was able to get from tuning the coil myself.) the radio, from my expierence wil only TX and RX within about a 5-6 meg range, depending on where the VCO coil is tuned. no service monitors are needed, tho would be better i'm sure if you had one. the VCO coil is located in the lower right area of the circut board looking down at the radio with its front cover removed, it is by the RX filter or RF preamp. the VCO coil has a round body with a round hollow tube sticking out of the top, it is the only one like it.
you will need a tweaking stick, kinda like an old color tv tuning stick, made of plastic, ( donot use metal stick) and have the plastic stick be a flat head and very narrow to fit down the shaft of the VCO coil. you will need to have the radio on, and watch the TX light as you tweak. if the frequency you are set to is out of tune, the tx led will pulse or flash, as you tune the coil around you will see the light go solid on, you are now getting the VCO into range of your freq. i woulld recoment you do this to your highest ham freq and your lowest ham freq, ALSO, i noticed at first that if the vco was not tuned perfectly, that as the battery would drain down, it would start to flash on TX, so this gave me an idea to fine tweak the radio when the battery was about 25% capicity, and sure enough i got the tweaking more exact. I HOPE MY NON SERVICE MONITOR WAY OF TUNING THE MX HAS NOT ANNOYED ANYONE, BUT HEY, I'M CHEAP. any way hope that helps, if you PM ME i can give you some addl info...

[KA1AXY]

Thanks for the tips!

I've seen the preselector, and it's a 72A2 (bummer, I guess)
Can someone confirm that this is the "wrong" module for ham band coverage? Didn't see any "61A" modules...

But, I did manage to remove the pin!

My four-channel is now a 12-channel.

It was much easier, once I pulled the final amp plug-in. That allowed me to get the switch completely out of the front panel. There was a black washer between the switch and the front panel, then, just as the previous poster said, a layer of RTV? over the pins. The one you need to pull is the one above the number "4" on the switch body. The one between "12" and "1" is the one that stays in. Photo attached (maybe). It shows the sequence of washers I removed, the switch and the small object just below the switch is the pin I removed. The white thing inside the radio is a piece of packing popcorn I used to position the switch so you could see it, and the 4 channel knob is just out of the photo to the left.
Hope this helps the next guy who tries this.

My radio now "beeps" when I try to transmit on the unprogrammed channels.

Next comes reprogramming...wish me luck!