Batboard

Hello. I have Gp340 that I try to repair for a long time. It seems to have two problems. It can not start and it can not be turned off.

After years of good working order radio first started to drain battery and making some strange noises while turned off. Soon it could not turn on at all. after I placed board on the bench I see that radio can not shut down after turning power on off switch. Mosfet Q400 is still turned on and can be turned off only if power supply is removed from the + and - contacts. I tried to change a lot of components from the good radio one by one and problems are still here.
Board is 8415234H09.
When I say it don't want to start here are the details. There is no green led on startup check. Only short plash and no sound. All voltages seems to be present. Unswitched B and SwitchedB to regulators and 5 and 3,3 V from the regulators.
One thing that is bothering me is that there is some voltage about 1,3 to 1,9V on the pin 4 of the Q405. it comes from the BATT_CODE pin and I don't know what it does and how it comes there. On the good board of the gp340 that voltage is not present.

If someone is willing to help I can write other details. So far I tried to change these parts: Q400 Main power MOSFET. Q405 dual transistor. VR506, CR411, CR412, CR413 diodes. R414 and R415 and Q417.
I prepared one page of the service manual where these parts are located but I can not find the option for attaching this page here in this post.

Many thanks.

Check TP406. It should have 7.5 approx when radio is on and a low voltage when radio is off. To test turn radio off connect to TP406 and apply power to battery connector plus and minus conn. You should read a low voltage maybe 1 or 2 volts max.
Turn radio on tp406 should raise to power supply voltage and stay steady. Please advise what happens.

35echo wrote: ↑

Mon Mar 11, 2024 11:39 am

Check TP406. It should have 7.5 approx when radio is on and a low voltage when radio is off. To test turn radio off connect to TP406 and apply power to battery connector plus and minus conn. You should read a low voltage maybe 1 or 2 volts max.
Turn radio on tp406 should raise to power supply voltage and stay steady. Please advise what happens.

Hello, thank you for reply. I follow you here but here is the thing. I have removed before many of the shield covers to investigate problem. I have removed it from the power control section, CPU, ASFIC, Synthesiser, even RAM ROM section. When I turn off the radio on the switch, I see no voltage on the switch but MOSFET Q400 keeps on powering the board. There is 7,5V on its drain and source ( SWB+) and the TP406 as well.

There is another transistor that powers the board during flashing the ROM. That transistor might be leaking. I am at home currently and will not have the schematics until Monday
18 March. This transistor only powers up some of the circuits but I don't remember exactly which ones. I do remember troubleshooting a leaking one before.

35echo wrote: ↑

Fri Mar 15, 2024 3:53 pm

There is another transistor that powers the board during flashing the ROM. That transistor might be leaking. I am at home currently and will not have the schematics until Monday
18 March. This transistor only powers up some of the circuits but I don't remember exactly which ones. I do remember troubleshooting a leaking one before.

Hi again. I think I checked that possibility also. That is Q417, dual transistor. Well, after all, maybe its not worth the trouble.
I spent a lot of time under that board just out of curiosity to find out what the problem could be, since I found on the internet other similar problems on other Motorola radios that can not be turned off.

Replace the flashrom.This is the most common problem (rotten terminals inside the Atmel chip),when the radio will not turn on anymore.