GP300 tuning/ alignment problem?

Josh · Post by **Josh** » Tue Dec 04, 2001 12:38 pm

I am having a few problems with a newly acquired old (1993) GP300 radio. It was in an accident at one point in its life (possibly a huge drop) that broke the case, shattered the battery off, broke off one of the battery guide rails and broke the on-off volume knob. The former owner bought a new case, battery, etc, but left me to fix the on off switch! (this radio was free).

Anyway, my problem is I can program it the way I want to, but something is mis-aligned in the radio that is stopping the radio from transmitting/receiving distant repeaters, when another radio from the same year, programmed the same way will- at the same squelch and power level. I thought it was a bad contact with the antenna, but it checks out o.k. I think that the two pots inside the radio may have been toyed with- I can only get good reception at close range with the radio now. I know a question lke this came up in the past on the old forum, but Does anyone know what I need to do to realign the radio's pots?
Thanks
-Josh

Post by **alex** » Tue Dec 04, 2001 1:23 pm

Sounds like the radio needs a good tuning using a service monitor, and some other fancy expensive toys

I would take it to a service shop that has this stuff, and let them look at it.

I have had this problem with a few other radios (not specificly this model your talking about) but sometimes the radios get different codeplugs that cover other frequency ranges that the hardware isn't compatable with. Like a 403-430 radio with a 450-480 codeplug. It will recieve (barely), but not the way it should.

Hope that helps.

-Alex

Will · Post by **Will** » Tue Dec 04, 2001 1:24 pm

Check the antenna test jack, a small jack under the antenna mount on the radio top plate. They fail real easy! Also there is a contact from the antenna circuit on the board to the antenna mount threaded bushing on the case, it could be bent or missing.

raymond345 · Post by **raymond345** » Tue Dec 04, 2001 2:29 pm

yes the ant port is a fault that i have
had a number of times. The service monitor finds it every time.

Josh · Post by **Josh** » Tue Dec 04, 2001 3:05 pm

Itis going to cost me big for this! The radio shop charges outrageous prices- $35 for an estimate, and like $60 per hour for labor.

I did a little testing of the radio with another, similar radio, and found that range from the god UHF radio to this radio, (both without antennas) was only about 2 feet, at 2watts. I didn't test it with the antennas on, but I know it to be a significant improvement so I don't think it is an antenna issue. I am beginning to think that perhaps when the radio shop originally fixed this radio- back when it fell and got broken, they may have put in the wrong board. The guts of the unit resemble my VHF radio more then it resembles my other UHF GP300.

The board in the radio is stamped HLE9676A...According to the Motorola page, this is a UHF Motherboard...I will see what the shop can do.

Does anyone know what the two pots in the radio are for? One for TX, one for RX, or both for overall radio TX/RX?

-Josh

<font size=-1>[ This Message was edited by: Josh on 2001-12-04 18:09 ]</font>

Josh · Post by **Josh** » Tue Dec 04, 2001 3:11 pm

On 2001-12-04 16:24, Will wrote:
Check the antenna test jack, a small jack under the antenna mount on the radio top plate. They fail real easy! Also there is a contact from the antenna circuit on the board to the antenna mount threaded bushing on the case, it could be bent or missing.

Checked that out. These parts, especially the contact with the housing appear o.k. I did a continuity test with it and it does make god contact with the pieces designed for the antenna adapting jack, and is not shorted to ground in any way.

Tony Soprano · Post by **Tony Soprano** » Wed Dec 05, 2001 5:10 am

That reminds me of a sure-fire antenna TX test. Take a plain old bayonet-base DC light bulb, solder a wire to the conductor at the base. Then, with the antenna off, hold the bulb at the glass and touch the wire to the antenna bushing threads, and transmit. Take care not to touch the wire, you'll get a nasty RF burn. If you have RF present there, the bulb will light. This also works with the antenna on, watch how the bulb lights as you move higher up the antenna. If you jack into a radio and see full power, and the contact is not touching the bushing in the housing, no radiated power.

Tony

Will · Post by **Will** » Wed Dec 05, 2001 1:14 pm

Tony, That reminds me of the LAPD radio shop's Tijuana Watt meter.... a #47 lamp with
17 inch leads from the two contacts. They would hold the TjWM by one lead and measure the power on the PD car's radio. This was the first test done when a car came in complaining of a radio problem. PS good to see you back here, Tony.

Josh, getting to your problem if you are still having trouble with your GP300 I can repair most problems for a LOT LESS than most shops. I have some special test jigs for the GP300's. One of my main goals being here on the BatBoard is to help in any way I can drawing on my thirty-three years in two-way radios.

Tony Soprano · Post by **Tony Soprano** » Wed Dec 05, 2001 1:54 pm

Thanks Will, actually never left but have had a lot of "irons in the fire". I figured I'd get poo-pooed on that one, but it works and little shop secrets like that keep it interesting.

Tony

Josh · Post by **Josh** » Thu Dec 06, 2001 9:56 am

Will:

E-mail me your address off-list or through a private message so I can send it to you. Also, in that message, tell me how much things will cost if all it needs is a tune-up.

Readers:

Made another discovery. The radio is no longer allowing me to transmit on any frequency beginning with 467. I don't know why. The Red light does not light, and when it does, it is not on the frequency programmed to transmit on at all. It works fine TX and RX (even though range is not good) on 462Mhz frequencies, as well as others aroung 467 (466~468)
Any ideas now?
-Josh