Great!
Besides the soft wire and internal losen,any possibility the switch power supply having problems?i can hear the switching power supply after turn on a while there is a da da da...sound and it stops the sound after few da..any clue?
i dont have a scope can do scanning for the waveform of the buttons board.
Thanks
Besides the soft wire and internal losen,any possibility the switch power supply having problems?i can hear the switching power supply after turn on a while there is a da da da...sound and it stops the sound after few da..any clue?
i dont have a scope can do scanning for the waveform of the buttons board.
Thanks
I really don't know such a kit but those sound as you say, seems not to be normal. Are the other functions normal (backlight, characters at display, fan). This may indicate correctness or not of the psu.
If the set is relatively old (say, ten years), the psu may need to replace the self maintaining cap. As an example, if the psu uses a UC384x there must me a +/- 100uF @ 25V cap where a +12V is generated to maintain the UC384x powered. If such cap is severely degraded, the PSU cycles without stabilizing any voltage. If you feel skiled, try to open the set and take a pic, but with the set unpluged. Dangerous voltages and live points may be inside it.
If the set is relatively old (say, ten years), the psu may need to replace the self maintaining cap. As an example, if the psu uses a UC384x there must me a +/- 100uF @ 25V cap where a +12V is generated to maintain the UC384x powered. If such cap is severely degraded, the PSU cycles without stabilizing any voltage. If you feel skiled, try to open the set and take a pic, but with the set unpluged. Dangerous voltages and live points may be inside it.
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This is a common problem with press buttons - the PCB has likely developed a hairline fracture due to repeated pressing over the years, and this has taken out a row or column of the virtual key scanning array.
I am presuming you mean "buttons are not all responding" rather than "none are responding". The latter could be many causes.
It always pays to check for loose connectors in old equipment BTW - unplug and reseat them all can catch problems.
Hi Mark,
I looked at the keyboard PCB it seems that there is no crakes or hairline on it and the soft wire connection to the keyboard PCB also good connection.
No loosen parts inside the machine either.
The tester had tested and work few months ago but seated and unplug for a while till recently turned on and malfunction.
The keys on the panel are all not responding now,not just some or one key work.
Regards
Alf
I looked at the keyboard PCB it seems that there is no crakes or hairline on it and the soft wire connection to the keyboard PCB also good connection.
No loosen parts inside the machine either.
The tester had tested and work few months ago but seated and unplug for a while till recently turned on and malfunction.
The keys on the panel are all not responding now,not just some or one key work.
Regards
Alf
Attachments
Another common defect with these molded membrane keypads is increased button resistance over time.
With an ohmmeter and some patience, you should be able to sketch out the switch matrix presented to the header pins. Try comparing resistance of working switches with the problematic switches. Deteriorated resistance might be revealed.
Assuming you find suspect switch resistance, usually you can carefully tease each of the molded studs that anchor the membrane through its respective hole and free the molded pad from the PCB without damaging the membrane. Often cleaning/gently abrading the problem pad will help, at least for a while. Adding conductive inks can work wonders.
Good luck!
With an ohmmeter and some patience, you should be able to sketch out the switch matrix presented to the header pins. Try comparing resistance of working switches with the problematic switches. Deteriorated resistance might be revealed.
Assuming you find suspect switch resistance, usually you can carefully tease each of the molded studs that anchor the membrane through its respective hole and free the molded pad from the PCB without damaging the membrane. Often cleaning/gently abrading the problem pad will help, at least for a while. Adding conductive inks can work wonders.
Good luck!
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If it is Chinese...
You are in difficulty.
It may be possible to fabricate a new keyboard using switches salvaged from a mechanical computer keyboard, or something similar. You will have a PCB to make, and a lot of soldering to do.
Or look for the same type of membrane / mechanical keyboard on line.
You are in difficulty.
It may be possible to fabricate a new keyboard using switches salvaged from a mechanical computer keyboard, or something similar. You will have a PCB to make, and a lot of soldering to do.
Or look for the same type of membrane / mechanical keyboard on line.
This is similar to TV remotes, a rubber molded keyboard with conductive pads.
Clean PCB and rubber with iso alcohol, and see what happens if you connect a row wire and a column wire.
Sitting there it may have gone resistive.
You get conductive ink and conductive stickers to repair those, but long term you need a new set of mechanical keys.
Clean PCB and rubber with iso alcohol, and see what happens if you connect a row wire and a column wire.
Sitting there it may have gone resistive.
You get conductive ink and conductive stickers to repair those, but long term you need a new set of mechanical keys.
I can't see IC markings clearly enough to speculate. Marking on the IC under the paper label might be a clue. Close-up pics might help, but you're venturing into very difficult territory, especially if you don't have a scope. Manufacturer still in business?
Do you recall if you needed to press a key to proceed beyond sign-on logo? I'm toying with the possibility that keypad scanning ICs are at fault.
Do you recall if you needed to press a key to proceed beyond sign-on logo? I'm toying with the possibility that keypad scanning ICs are at fault.
so if i measure the keypad conductive resistance how many ohm should it roughly like to be normal?
but the fact is all keys are not working?possibility all keypad conductivity all gone?
when i press any key,i dont get any beep sound.