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htx 100 help

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  • 1 Post By unit_399
  • 1 Post By TonyV225
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  #1  
Old 08-12-2012, 06:51 AM
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Default htx 100 help


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!


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Old 08-12-2012, 10:34 AM
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Ddog -

Intermittent problems can be a bitch to solve. The first thing I would try is to perform a reset while monitoring the voltage (5v) on pin 64 of the processor. If the voltage fluctuates or drops significantly, do another reset but monitor the output of the 5v regulator (IC405) directly. If the voltage fluctuates here too, replace the regulator. If it holds steady, check the 5v path to the processor for bad solders or intermittent connections. If the voltage at pin 64 holds steady during reset, then the problem is probably with the processor itself, or possibly with one of the oscillators. Since the rig doesn't work at all now, digging much deeper than this will be difficult. If you get to this point without success, about the only thing left to do if to thoroughly go over all the boards looking for an open circuit or bad solder joint(s). Use a jeweler's eye loupe. Good luck & 73s.

- 399
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Old 08-12-2012, 02:14 PM
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This exact problem happened to my Yaesu FT-990 base rig years back after several years of trouble free use. I did all the obvious like Master reset and a few otherthings with no prevail. I sent it out to Burghardt Amateu Radio Repair and they fixed the problem which was nad solder joints on the front panel or board. They said that over time this happens.

They fixed it shipped it back and its been trouble free once again for about 3 years or more nowjust something to think about because solder joints are about 80% of most issues even more so now days.
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Old 08-12-2012, 03:03 PM
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@unit_399 & tony, thanks mates!

will do as advised and will try to do your tips and report back my findings
thanks again !

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Old 08-12-2012, 03:20 PM
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If you suspect the IC is bad, consider reducing the value of the pull-up resistor. If the IC has an internal short on one of it's junctions, the chip with get hot as the current is increased. On rare occasions this can actually pop the short out and restore operation. Don't get your hopes up on that though because more often then not it just confirms the IC is dead.The problem could easily be bad or shorted connections from one board to the other as mentioned. This advice is just to help you determine if the IC is shorted.
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Old 08-13-2012, 06:29 PM
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@shockwave; thanks for the tip, will do as advised and will update what happens
btw, i've checked the 5v on the cpu,it rock stable throughout, tnx!

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Old 08-13-2012, 07:58 PM
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chip switch will be the best deal,if you can find one...was a great thing back when i ran them and 2510s and 2600 rad shack htx100 is a stripped down 2510...73 de JW
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Old 08-16-2012, 12:43 AM
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fixed it finally!

this unit gave me sleepless nights and got me stumped for awhile

the fix couldn't be less simple

it was just a glue that has become conductive due to aging

the 5v regulator supplying the cpu was glued to the board and it sits directly below the pins for front panel buttons. this glue becoming conductive (it reads K-ohms) made the 5v disappear at pins 41 and 42 making the cpu think the FLock switch is "on" (locked mode)

out of desperation, i "cleaned" the cpu board by removing all glue on the board and much to my delight, this solved the ailment of my htx100

thanks for all the help! 73!

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