Batboard

I have a Motorola Radius mobile, low band radio that programs fine and transmits fine. When first programmed, it received three transmissions, after that it hasn't received since. If you open the monitor circuit, it sounds like an open channel (meaning that the squelch is there loud and clear, but it won't receive anything when your transmit from another radio). It sounds like its programmed on the wrong RX frequency, but after verifying that is not the case. Any ideas what might cause this problem? Thanks.

- Rob

Hello:
The LOW BAND radius line along with maxtracs have a known history of losing the rx but still tx just fine.
Sounds like you have run into one with a defective 10.245 mhz crystal which if you have a repair manual is schematic part Y52.
Motorolas part number is 48-80908w01
Also if the 10.245 mhz crystal is working you should be able to get a scanner near by to pickup the 10.245 mhz crystals freq .
If the scanner doesnt hear it then id be willing to bet the Y52 crystal is dead.
The 10.245 Y52 crystal is for recieve only and does not affect the tx.
Since you mentioned it recieved a couple of times then nothing -- could it be a bad solder or did by chance the audio jumper on the back of of the radio come loose.
The jumper for 15 to 16 pin must be in for rx audio on a 16 pin logic bd type radio.
If by chance you have a 5 pin logic bd then no jumper for rx audio is required and not you trouble.
Its located on the rf bd of the radio and if you have a Maxtrac / Radius M series mobile laying around you could rob the crystal and solder it into your radio.
But you will need to warp the replacement crystal onto freq by using a service monitor and the rss program made for the radius series mobile to make it work corectly after replacing the crystal.
The crystals are not all exactly alike and will require proper tuning for proper operation.
Another possibilty would be the interconect pins that conect the logic bd to the rf bd could be in need of a good cleaning to make contact but id say probably not likely in your situation.
Good Luck
Satelite

Thank you! I will try to replace that crystal from one of my parts radios... I appreciate your help.

More bad news... Finally got the radio on the bench and now its saying its transmitting, but I am not receiving anything on my receiving radio or scanner. It was TXing fine, but not receiving - now its still not receiving or transmitting. Any ideas?

Hello :
Did you by chance replace the crystal on the bd described in earlier posting?
And did you positively replace the Y-52 crystal or by chance replace the wrong one ?
Thats all i can tell you with out actualy having it on the bench for testing.
Satelite

Didn't replace anything yet, just got it on the bench and found it not receiving or transmitting.

by any chance did you program it out of band freqs? if you did, the vco and alignment needs to be touched up maybe. did you hold down the shift key while entering the freqs???. some earlyer radios spread freqs better than the newer ones and you did not have to re tune anything to get them to work out of band. just a idea.......

Hello :
Well with the intermitant works and doesnt work situation in both rx and tx modes now that you didnt notice before it will be a bit more dificult.
But lets check a few things out first.
Is the power supply your using to power the mobile big enough to supply the voltage and amps needed to tx the mobile ?
Too small and its not going to be dependable.
Take the rf bd and logic bd out and clean the interconect pins in the chassis to make sure you have a good clean contact.
Also clean the conectors on the two bds and reassemble and see if things dont come back to normal.
If you can confirm these to be ok then id further check into trying another pa if you have one and see if its causing the issue.
Good luck
Satelite

Thanks for the replies... I didn't program it out of band, and I am using a 50 amp power supply - so it should be good... I will disassemble and check the boards you mentioned. Thank you both for the replies!

- Rob

Thank all of you for your help. The radio is fixed!! The crystal was the issue. After it was replaced - she works perfectly!

Hi everyone,

I'm also facing the notorious 'no RX issue' on my GM300. What kind of crystal is this Y52 exactly? Is it something Motorola-specific, or can I just order it at a specialized company which produces xtals? Is there something specific to pay attention to?

Greetz, Ronald

I believe that the GM300 RF board is not the same as the low band Radius or low band maxtrac so I'm not sure of the 2nd LO crystal frequency or its designator.

Also for future reference the VHF high band radios use a 2nd Lo crystal, Y52 designator, that is on 44.645 MHz and these were know to drift off by a couple of KHz either resulting in distorted RX or no RX at all.

I just replaced 2 X 44.645MHz 2nd LO crystals, one in a VHF high maxtrac and one in a 220 MHz maxtrac this past week (the 220 radio used to be a VHF high model in a previous life).

The VHF low band maxtracs and radius line uses a 10.245 MHz 2nd LO crystal, also Y52 designator, and this is most likely the crystal that was replaced in the radio in this thread.

Also Rob, I'm curious as to what crystal you ended up changing in your Low band radio was it Y52? If so then is the replacement a 10.245 MHz crystal?


Mike

Hello:
GM300 also calls the 44.645 oscilator crystal Y52 and yes obove poster is corect the bds are difererent but use the same crystal.
GM300 mobiles do have a known problem of the Y52 oscilator crystal going bad which will cause no rx.
But make sure you have the 16 pin adaptor plug installed on the rear of the radio because if its not there will be no rx audio but radio should flash red on front if it is recieving.
Id also make sure the interconect pins are making contact from the logic bd through the chassis into the rf bd.
If they arent then you could loose rx.
I simply without removing the bds loosen the screws on the bds and with a pair of pliers grab the metal and gently pull up and push down to make a better contact for testing only on both bds then retighten and see.
But i do recomend cleaning the interconect pins if it seems to solve the issue.
This Y52 oscilator crystal is the same crystal used in the maxtracs and looking at my GM300 parts book the part number is 48-80008k02
The crystal will be located on the rf bd which is the one that you will see two small coax cables that plug into the bd from the rear pa deck.
Its a small crystal and usualy has some rubber cement type glue at its base from factory and will have 44.645 printed on it.
If you have a maxtrac that you could rob parts that crystal is the same beast.
After replacing y52 crystal make sure you check that its still on freq otherwise if not warp it back on with thr rss program and a service monitor.
I believe i read some where that the crystal could be bought from another company but dont recall the actual info now.
I use motorolas crystal myself so i didnt really put it in my memory for future use.
Good Luck
Satelite

Curious now, I wonder if all the bad 44.645's Xtals were made by TOYOCOM?

I just checked my stash of bad ones that have been changed and all of mine are TOYOCOM crystals.

My 44.645 MHz replacements are an ICM part # 48-80008K02 even though it is a standard ICM cataloged part they make them immediately after the order is placed and then they age them for 2 weeks.

I have 2 remote bases running on 6 meters and 10 meters using maxtracs for close to 8 years now and never a problem with them but the 2 VHF radios that I just replaced the 2nd LO's in were recent additions to my collection.

Now that I think of it I haven't heard a squelch open in a couple of weeks now on either of my low band maxtrac remote bases, maybe it's time to check their 10.245's to see if they have drifted.