I recently acquired a working realistic htx100 (not modified), but before i was able to fully enjoy it, some of the front panel buttons stopped working - behaving just like the F Lock switch is on ( freq knob, up/down sw, memo and mode doesn't work)
this was intermittent at first, behaving like that after warmup or sometimes even if the unit is still cold
i cleaned the F Lock switch just to be sure but it isn't the problem
probing around the cpu (ic402 - uc1208 Uprocessor) area i found that pin 42 (F lock pin) is low (the manual says it should be 5v) and it should go low only when F Lock is switched. pin 42 is not shorted to ground hence i suspected the pull-up resistor
just touching the pullup resistors restored normal operation but after the set was closed it locked up again and the display now shows intermittent "TX" too. i resoldered the pullup resistors again and it cleared the problem, however after plugging the antenna the radio does not receive anymore
i reset the unit but after that the radio didn't worked anymore, no rx/tx, all the front panel button does not work anymore only a hissing sound (squelch and volume worked) a blinking 28.000 is on the lcd
the microprocessor pins 41 and 42 now reads 0V, i replaced the pullup resistors (RR405) but didn't cure the problem
i followed the troubleshooting flowchart on the service manual, reset works (pin 43), clock is ok (shows 1.9999 mhz on my counter) pins 17 & 16 reacts every time the VFO knob is moved, pins 10, 9, 8, 6,5 4 reacts everytime a button is pressed but no beeps heard, 5v supply is available, only that pins 41 & 42 is OV where it should be 5V, the displays shows a blinking 28.000
i have run out of ideas and WITH no definte source of spareparts, i am now beginning to think the CPU is no longer responding (pins 41 & 42 might be internally stucked low)
any ideas on what to do next? thanks and more power!
this was intermittent at first, behaving like that after warmup or sometimes even if the unit is still cold
i cleaned the F Lock switch just to be sure but it isn't the problem
probing around the cpu (ic402 - uc1208 Uprocessor) area i found that pin 42 (F lock pin) is low (the manual says it should be 5v) and it should go low only when F Lock is switched. pin 42 is not shorted to ground hence i suspected the pull-up resistor
just touching the pullup resistors restored normal operation but after the set was closed it locked up again and the display now shows intermittent "TX" too. i resoldered the pullup resistors again and it cleared the problem, however after plugging the antenna the radio does not receive anymore
i reset the unit but after that the radio didn't worked anymore, no rx/tx, all the front panel button does not work anymore only a hissing sound (squelch and volume worked) a blinking 28.000 is on the lcd
the microprocessor pins 41 and 42 now reads 0V, i replaced the pullup resistors (RR405) but didn't cure the problem
i followed the troubleshooting flowchart on the service manual, reset works (pin 43), clock is ok (shows 1.9999 mhz on my counter) pins 17 & 16 reacts every time the VFO knob is moved, pins 10, 9, 8, 6,5 4 reacts everytime a button is pressed but no beeps heard, 5v supply is available, only that pins 41 & 42 is OV where it should be 5V, the displays shows a blinking 28.000
i have run out of ideas and WITH no definte source of spareparts, i am now beginning to think the CPU is no longer responding (pins 41 & 42 might be internally stucked low)
any ideas on what to do next? thanks and more power!