GM300 powerup weirdness

Tom · Post by **Tom** » Mon Apr 08, 2002 10:28 am

Greetings,

anyone have any clues to this this?

If the repeater is turned OFF for some number of hours via the main power supply switch and the transmitting GM300's pwr/vol control is left in the ON postion, the next time I turn the GR300 system on via it's main power supply switch the transmitting GM300's display remains blank (although the pushbutton backlights can be seen). The buttons do no react and no power up beep is heard.

If I then turn the radio OFF then ON again via it's pwr/vol control while system power is still on, all is then fine! I can even power it OFF momentarily with main powersupply switch and turn it ON again and the transmitting radio then powers up fine again.

Once that's done, I can then power down and up the system via the power supply switch for quite some time afterwards without trouble. The radio transmits and receives fine once it's "alive" the first time.

The transmitting GM300 will also power up just fine the first time if the GM300 has been switch OFF before I turn the repeater on via the power supply switch, then turn the radio on afterwards.

This occurs regardless if the transmitting GM300 is connected to the RICK or not. Powersupply voltage measures 13.8V).

The receiving GM300 does not exhibit this problem (although it seems to be configured to power itself on even if it's turned off at the pwr/vol switch as long as the main power is on). Normal??

BTW - I am very new to the Motorola scene... Hope to be able to do something with this repeater reconfigured for the 440 Ham band. Both radios are M34GMC29C3AA models.

thanks and 73's

tom

jim · Post by **jim** » Mon Apr 08, 2002 1:26 pm

Most radios are not designed to have their power feed go from 13 volts slowly downward to 0 volts, as turning off a power supply does (it does this from draining of the capacitors). I would install a 30 amp rated SPST switch on the (+) output of the power supply and switch this off before switching off the power supply's power. This way, the radio will "see" 13 volts and instantly 0 volts, as if it were in a vehicle and shut off. Low voltage can do funny things to some electronics. It's never a good idea to "underfeed" any electronic device. Some can even be damaged!

Anybody else have another idea of why it is actually doing this?

Post by **wavetar** » Mon Apr 08, 2002 4:56 pm

Your theory sounds likely. I've never seen the problem myself, but then again, I generally just install them for clients & leave them be. No powering on/off.

Todd

Nand · Post by **Nand** » Mon Apr 08, 2002 6:32 pm

Will · Post by **Will** » Mon Apr 08, 2002 8:06 pm

Nand, this is true and this is one of the problems I addressed when engineering and testing my own modules.
I am working to find out why this ocasionaly happens, so far it does not occur with my repeater module.

For now, you mite try turning off the Emergency input on the accessory jack in both radios.

Nand · Post by **Nand** » Mon Apr 08, 2002 8:44 pm

Tom · Post by **Tom** » Tue Apr 09, 2002 11:23 am

Hello and thanks guys for the tips.

Since the blank display also occurred with the radio disconnected from the RICK, I'm guessing it's the radio, too.

I've seen similar problems with other microprocessor power-on reset circuitry and typically they've turned out be something like a marginal tantalum or electrolytic cap. if present.

Took a quick peek inside the radio, under the CPU cover and no obvious signs of discoloration from overheating. (The tantal caps I've seen fail tend to develop shorts and overheat!

Unfortunately I don't have any schematics and docs for this radio or the RICK so I guess I'm just going to have to live with it and power it up via the radio's own pwr/vol knob.

Regards!

tom