GM300 Deaf

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eagle844
Posts: 68
Joined: Tue Mar 24, 2009 5:05 pm

GM300 Deaf

Post by eagle844 »

I have been reading about deaf vhf gm300. The articles say it could be the 3 leg diode or the crystal. Is there a way to test the diodes while still on the board?
If so, I have done this and got some values on the diodes.

Could any of you put up a picture of the board where the diodes and crystal that needs replacing to get the radio in working order?

Thank very much

Mike
guy being a guy
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Re: GM300 Deaf

Post by guy being a guy »

By "deaf" I'm thinking you mean no RX ?
If the TX side is fine ( ESPECIALLY being on frequency within say 500hz) AND you have no RX .............The 14.4 crystal is NOT the problem !
IF you are WAY off frequency on the TX side here is what you can do..................
First double check you have the correct RX freq. and NO green flashing lite on control head . Flashing green lite means it IS receiving , but you have NO audio.GM300 can have a bad audio amp on the logic board - it will get VERY hot when it's bad.
Go to the RF board , remove the smaller "L" shaped shield and locate the small metal crystal - there is a trimming potentiometer right next to it. Set up your freq. counter to measure 14.4 Mhz. Must be a very sensitive and acurate counter.
Place your probe right on top or the crystal, using a PLASTIC tuning tool adjust that 14.4 crystal to EXACTLY 14.4 ! Within 5hz !
Must be dead nuts 14.4 mhz !!!! Its the reference oscillator for the entire radio.
Check RX AND TX freq. error...................OK ?
If not, that radio is so old I would buy a boat and and some rope.
I have seen some coils open in the selector tanks under the board as well as some RF amplifier transistors, but the time to get into that level of repair far outweighs the value of your new boat anchor .
eagle844
Posts: 68
Joined: Tue Mar 24, 2009 5:05 pm

Re: GM300 Deaf

Post by eagle844 »

Yes the radio does not have RX. I do not have the equipment to do all that. The Radius GM300 does not have a green light for RX. It flashes red. At this point I am not sure I will be able to repair these units.

Thanks anyway,

Mike
AEC
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Re: GM300 Deaf

Post by AEC »

Try inputting a signal into the receiver, and if you have no response, check the 2nd oscillator, it should be a 44.645 mhz. crystal, and is the middle of three near the left side of the board, between two shielded inductors (tunable).

The 2nd oscillator is a common weak point, they go bad and swing outside the factory tuned frequency, and at times, a heat or cold treatment will warp it back, but many times, no.

On channel reception or lack thereof is a good indicator, as is a loss of sound in the receiver when the squelch is opened. If the 2nd oscillator is off, you will need to inject a hefty signal to get the receiver to wake up, and then look at the actual error frequency, once you note the direction the error is, positive or negative, then tune the generator to that frequency and check the level required to open the receiver. No matter what, you will need to replace it.

It's just nice to know how far the crystal moved from the 44.645 mHz. center.

I will snap a pic of actual crystal placement shortly, once my snow plowing is done (yuck).

Here's the pic showing the location.
Image

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Will
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Joined: Tue Sep 04, 2001 4:00 pm

Re: GM300 Deaf

Post by Will »

Opps! that is the crystal filter in the first IF.

The second lo crystal is to the left and down from that.
AEC
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Re: GM300 Deaf

Post by AEC »

Too fast on the trigger, was wet from blowing snow, ran in and snapped a pic and went back to removing the white junk.
guy being a guy
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Re: GM300 Deaf

Post by guy being a guy »

Don't mean to be "mean"........
How do you expect to repair a receiver without the proper equipment and knowledge ?
We are here to provide the knowledge and advice, but it sounds like maybe you need to pay the "radio man" .
Not being mean , but when a person asks for advice here we expect SOME kind of resources or basic knowledge .........
Google "Motorola radio shop" followed by your city and state ..........Best we can do for 'ya - sorry .

I forgot abot that 44.645 xstal going out ..........If you had a frequency counter you could check, but I digress........
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wavetar
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Re: GM300 Deaf

Post by wavetar »

guy being a guy wrote:Don't mean to be "mean"........
How do you expect to repair a receiver without the proper equipment and knowledge ?
We are here to provide the knowledge and advice, but it sounds like maybe you need to pay the "radio man" .
Not being mean , but when a person asks for advice here we expect SOME kind of resources or basic knowledge .........
Google "Motorola radio shop" followed by your city and state ..........Best we can do for 'ya - sorry .

I forgot abot that 44.645 xstal going out ..........If you had a frequency counter you could check, but I digress........
There are over 23 thousand members here...a huge percentage of them do not have what you may consider even 'basic' equipment. Try to keep this in mind when answering and giving a helpful post.
No trees were harmed in the posting of this message...however an extraordinarily large number of electrons were horribly inconvenienced.

Welcome to the /\/\achine.
Satelite
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Joined: Sat Aug 12, 2006 10:43 am

Re: GM300 Deaf

Post by Satelite »

Hello eagle844
You may have a problem with the crystal but im going to just mention another possibility.
I read above you said the gm300 didnt have a green light it flashed red on rx which is corect.
But if the radio your refering to did flash red and you heard no rx then id say you did recieve signal just no audio.
On the rear of the gm300 radio there should be a 16 pin plug on the option port that actualy enables the speaker in the radio and if not there and only 16 pins showing then no audio.
There is info here on batlabs pertaining to this and you can jumper the two needed pins to get audio if in fact your missing the plug with the jumper.
If not your problem then please ignore.
Good Luck
Satelite
Will
Posts: 6823
Joined: Tue Sep 04, 2001 4:00 pm

Re: GM300 Deaf

Post by Will »

The speaker enable jumper is from pin 15 to pin 16, the last two pins, one above the other on the outside edge of the radio.
http://www.batlabs.com/images/gmacc8.gif
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