Electronics > Repair

UT805 repair

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mortos360:
After watching Dave's repair videos, I thought I try that too, since it looks like fun :)
So I bought a broken UNI-T UT805 off ebay and trying to repair it now... and.. it is fun :D    but I am stuck a bit.

I also wanna mention at this point that I really don't know much about electronics.. its a hobby and I like to play with in my free time, but I never really learned it, and got hardly any experience.
That said.. here is what I got so far...

The unit itself seem to work fine, but the display shows only garbage. I have connected it over USB to my PC and I did a few test measurements like resistance and DC volts, and it seems to work fine.
All the buttons on the front panel work too.
Here is an picture of the front panel:


 
The IC that drives the display seem to be an ES51986A and here is the data sheet: http://www.cyrustek.com.tw/spec/ES51986.pdf
It looks like this IC does also some of the measurement and since measurements (at least volt and resistance) works.. I guess the IC is not the problem, or?

I looked for any visual problems like burn marks, lose connections or solder, but I cant see anything that looks wrong.

Maybe some of you can point me in a direction?

Thanks! :)

mortos360:
Also another question.. where do you guys always get the service manuals?
I tried to google it, but nothing.

ElektroQuark:
I would check first contact between display and drivers,it looks like a mechanical (solder, connector,...) problem.

mortos360:
I checked them.. I also checked the driver... everything seems fine.
There is a IC for the keyboard and display interface: http://pdf1.alldatasheet.com/datasheet-pdf/view/102634/NEC/UPD8279C-2/+0037W7VlDwaUShwNDGKpw+/datasheet.pdf
He seems to actually sends commands to the display.. not sure I can test it, but I am looking into that now.

Chipset:
Probably not applicable but I have an HP 3478A that acted much the same way, turns out the +-15V rails for the analog stuff where completely dead. Presumably the regulators popped but I didn't bother troubleshooting, since it was just using 3 pin regulating IC's it was all of like $5 worth of components to replace the entire regulating circuitry.

As Dave says, the first rule of troubleshooting is check voltages.

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