Batboard

Hi, this is a HT750 radio that was working fine and suddenly developed a strange zombie like state. In all my years dealing with these older HT series radios never seen these symptoms. Not sure this radio was actually dropped, it looks clean no marks outside. When the radio is powered up a short low pitch (error) tone will sound almost immediately (it seems to take a bit less time than the normal high pitch Ok tone would take upon boot up), and the top LED will not flash at all. All option side and top buttons, including the PTT seem non operational, and only elicit a double short error beep like when the button has no assigned function, but beeps twice. In any case only the top orange button was enabled as a battery level indicator. The squelch seems to be open as there is some soft hiss audible through the speaker, but the level of the hiss is quite low even with the volume control fully clockwise. The radio had only ch1 and ch2 programmed, but it no longer gives the invalid channel continuous low tone on any position. It will not go into RF Test mode, CPS (or Tuner) cannot read or write to the codeplug, and after several minutes a comm error will come up, but the radio is definitively communicating in some way as it will sound a short error tone when the comm error comes up in the CPS. The only preliminary internal test I did so far, before I start to pull off shields, is to check the 16.8MHz crystal oscillator, and it seems fine. Could this be something similar to the dreaded EEPROM data corruption? ASFIC? I have a relegated "no power on" HT750 I could pull the EEPROM from to swap it out to at least see if that cures the zombie problem.

Any ideas anyone? Input much appreciated. Thanks.

Shot battery.. needs a new battery

Excuse me, but how can it be a battery problem if the radio boots up, sounds error tones when powered up and when side/top buttons or PTT are pressed, the 16.8MHz main oscillator is working....etc. Besides I never use a battery to test a radio on the bench. DOH.

I can also now add that both 3.3V (IC3201) and 5V (IC3711) regulator output voltages are on spec. Anyone have any USEFUL ideas before I pop off some more board shields?

Thanks.

If you do not already have one I would recommend you obtain a 6881088C46 Detailed Service Manual and go through the controller DC distribution since your controller appears to be only partially operating

But of course I have a service manual, how else would I be able to do some of the in-depth tests I just described? Otherwise on this radio it would be the equivalent of trying to take measurements with with a white cane and dark glasses. I do have 40 years experience with M equipment, including board level troubleshooting. Only this time I am a bit stumped at this problem which I never have encountered before, so was wondering if somebody belonging to the well informed group of people in this forum has ever seen something similar, or have any suggestions. I certainly appreciate any and all input, but please I don't need the 101 stuff. Thank you.