GP338/GP388 - fault - power cycling when switched off

[g8tzl2004]

I have just acquired a "mint" GP338/GP388 but with no battery.

When you attached a battery and the radio is still switched off, it goes into a constant partial power up loop - it bleeps, the green top LED lights up and the LCD backlight lights up...and then goes off..and then constantly repeats in a loop...bleeps, LED/LCD lights up and then off again. There is nothing on the display when it lights up , BUT when the backlight is off, there is a very small antenna symbol on the left and something else.

When you switch on, the radio appears to power up as normal - with "Channel 1" displayed. When you press the PTT, the red LED lights up. BUT there is NO detectable TX on a frequency counter..but some very limited power is being put out..enough to hear a change in backgound noise when RXing using wideband (200Khz) mode on a VHF receiver...its probably less than 1mW....I did not bother scanning thru to find the exact TX frequency.

On RX, the radio is detecting a carrier...you can hear a low level noise in the speaker...but no modulated audio is being received when you TX a test signal (but its nothing to do with CTCSS or other signalling).

I also noticed that the battery (which is a real Motorola battery) was not a great fit...the top of the battery is not exactly level with the top of the radio...its like the tabs on the metal back plate which the battery locks onto and too far out..almost as if the metal chassis is not fitted correctly..although I can see no obvious signs of a poor fit or of anybody having tried to remove the backplate. The top side switch also does not "click"..the bottom side switch and PTT have OK "clicks"

UPDATE: I left the radio powered up and just "receiving" for maybe 30 minutes...the metal chassis got warm and the flat battery bleep started !! PA issue ?

Any thoughts? I now know why the radio came without a battery!!!!!

[g8tzl2004]

Any ideas?

[Will]

Any ideas?

Yes, have seen this on other portables. The transmitter final is leaking and drawing current even when not transmitting. Usually replacing the final module fixes this.

[g8tzl2004]

Thanks Will. Does the leaking final cause the "constant partial power up" loop when actualy switched off and the RX problems?.or is there additional issues?

[Will]

Did you measure the DC power into the radio? Current?

[g8tzl2004]

Its a fully charged battery...but maybe the extra load from the PA leakage results in a voltage drop...but would this stop the radio from powering down? Even when switched OFF, the radio goes into a constant partial power up loop...basically with the battery attached you cannot power down the radio.

I bought the radio "as new" (but with no battery!!!) so I will definately not start delving but I want to be able to tell the seller what is wrong with the radio.

[Will]

g8tzl2004,
To check you would need to measure the current the radio draws.In the off and on modes. You may not have a battery eliminator and 7.5 volt power source. So that makes it difficult to measure with clip leads and a VOM.

I have seen them measure low ohms with a VOM across the DC connector on the radio.

I take one of that radio's batteries that is dead and cut it out to get to the battery to radio connector for testing. Kinda like a poor mans battery eliminator.

[CircleBat]

bottom right hand diode next to the flex connector.. very common problem.. needs to be replaced

CircleBat

[g8tzl2004]

Does the faulty diode cause the PA leakage ..with the chassis warming up while still in receive mode?

Or is it the diode which causes the constant power cycling even thought the radio is switched off at the volume pot?

[d119]

Diode = Power on problem

PA = warming up problem