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!