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 5155 display problems, potentiometers probably View next topic
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rv



Joined: 30 Oct 2004
Posts: 22

PostPosted: Tue Aug 20, 2019 5:07 pm Reply with quoteBack to top

hi there

I got myself this 5155 portable PC to mess with.

it looks as if someone upgraded it steadily through the 80's and even had a small (for an mfm type) hard drive screwed on a control board.

but the little amber display was giving me troubles.
the text, though legible with a bit of effort produces what looks more like amber blocks than letters.

I took it apart and looked for something obvious causing it such as a blown capacitor or something to no avail.
finally i did what i should have done before opening anything (even if getting rid of 30+ years of dust can't be bad)

I turned the contrast knob.
screen went beetween crisp text, blocks, flickering lines and no picture and then back to something in between those statesin an instant.

now I think that I have a reletively easy fix until I see that the pots have no information on them except for this string of numbers:
63-10770-15 137/8427
which when googled gives me this information: contrast knob

thanks internet

would any of you know what the value of these might be?
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T-R-A



Joined: 02 Oct 2004
Posts: 576
Location: Western NC

PostPosted: Thu Aug 22, 2019 9:48 am Reply with quoteBack to top

Hate to drive traffic to another site, but have you checked minuszerodegrees?

http://minuszerodegrees.net/
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rv



Joined: 30 Oct 2004
Posts: 22

PostPosted: Fri Aug 23, 2019 7:17 am Reply with quoteBack to top

I have been there and while there is significant amount of useful information there I have yet to find this.

however I have determined that the brightness pot is mostly okay.
I had thought both were destroyed by age.

later today i'm taking my ohmmeter on the thing and seeing if i get an useful value to order a component.

i should at least throw it here for the other three people in the world that might have this problem
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Puckdropper
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Joined: 02 Oct 2004
Posts: 758
Location: Not in Chicago

PostPosted: Mon Aug 26, 2019 5:40 pm Reply with quoteBack to top

Is the pot exposed where you can see the contacts? Maybe a contact cleaner like CRC-226 (get it at Home Depot, it's priced near $2.50 for a little can) can make it usable again?

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rv



Joined: 30 Oct 2004
Posts: 22

PostPosted: Mon Aug 26, 2019 6:09 pm Reply with quoteBack to top

ok, a little update.

after trying to measure these things and receiving unreliable results
I did find someone in a forum somewhere say 100kohm but he was talking about the 5151 monitor.

at any rate, I took them and sprayed with contact cleaner and moved them back&forth.
they have become stable.
and i can have the text crisp

see here:
https://imgur.com/a/7rVmyMz

turn it too far and it smears
https://imgur.com/a/kTjPiPf
not sure what's going on there but i'll take what i get.
it's not flaky anymore and that's what counts
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T-R-A



Joined: 02 Oct 2004
Posts: 576
Location: Western NC

PostPosted: Mon Aug 26, 2019 11:51 pm Reply with quoteBack to top

rv wrote:
ok, a little update.

after trying to measure these things and receiving unreliable results
I did find someone in a forum somewhere say 100kohm but he was talking about the 5151 monitor.

at any rate, I took them and sprayed with contact cleaner and moved them back&forth.
they have become stable.
and i can have the text crisp

see here:
https://imgur.com/a/7rVmyMz

turn it too far and it smears
https://imgur.com/a/kTjPiPf
not sure what's going on there but i'll take what i get.
it's not flaky anymore and that's what counts



That's typical of a potentiometer that's pretty much worn out. It would suffice to say the "ends" are worn away (and likely over-driving the display). If you're happy with the results, then carry on. Just make sure to keep the contact-cleaner available...you'll likely need it again until you decide to replace the pots.
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rv



Joined: 30 Oct 2004
Posts: 22

PostPosted: Tue Aug 27, 2019 12:07 am Reply with quoteBack to top

well, eventually i will probably replace them.

but for now this'll do, I can read the screen for the moment

this old thing is riddled with problems, which isn't surprising considering it's age.
the aftermarket hard drive squeals terribly and the keyboard needs thorough cleaning.
not to mention the boot errors that i've yet to attempt to diagnose.

i am still hoping that the squeal is coming from an external brush that i see in the bottom of tge drive rather than inside the bearing.

i might end up replacing that mfm on a card with a compactflash solution anyway.

i am still amazed that you could get an mfm on a card though.

at any rate, a thumb potentiometer seems to be the least of my problems.
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