19 Jan
2021
19 Jan
'21
3:09 p.m.
For a workaround:
1. Solder any same size pot with suitable long wires to the location (if possible)
2. Adjust the brightness to Your liking
3. Remove the pot
4. Measure the resistance
5. Solder a measured value resistor where the pot was.
This way You get a fixed brightness and somewhat working computer.
Now You can wait for a replacement pot and play with the computer.
BR Matti
19 Jan
19 Jan
5:28 p.m.
New subject: Looking for a potentiometer for restoration project
For a workaround:
1. Solder any same size pot with suitable long wires to the location
(if possible)
2. Adjust the brightness to Your liking
3. Remove the pot
4. Measure the resistance
5. Solder a measured value resistor where the pot was.
This way You get a fixed brightness and somewhat working computer.
Now You can wait for a replacement pot and play with the computer.
Thanks. We are not that bad off, yet. The system is fully working but the
screen brightness is way up so everything looks washed out and the screen
gets very hot. If I can't find a replacement I could always just leave it
alone or try to open the pot and see if I can repair the actual pot. If all
that fails the backup would be to either permanently solder in a resistor
(as you suggested) or use a pot with the same values which works but does
not allow the case to be closed.
I am hoping to get the correct part though.... I have found a replacement
pot for the speaker knob (same family, different resistance value) so I am
hopeful it may be just a matter of time.
5:47 p.m.
New subject: Looking for a potentiometer for restoration project
Out of curiosity, why do you think the pot is bad?
Wayne
Sent from my iPhone
On Jan 19, 2021, at 14:28, Ali via cctalk <cctalk
at classiccmp.org> wrote:
?
For a workaround:
1. Solder any same size pot with suitable long wires to the location
(if possible)
2. Adjust the brightness to Your liking
3. Remove the pot
4. Measure the resistance
5. Solder a measured value resistor where the pot was.
This way You get a fixed brightness and somewhat working computer.
Now You can wait for a replacement pot and play with the computer.
Thanks. We are not that bad off, yet. The system is fully working but the
screen brightness is way up so everything looks washed out and the screen
gets very hot. If I can't find a replacement I could always just leave it
alone or try to open the pot and see if I can repair the actual pot. If all
that fails the backup would be to either permanently solder in a resistor
(as you suggested) or use a pot with the same values which works but does
not allow the case to be closed.
I am hoping to get the correct part though.... I have found a replacement
pot for the speaker knob (same family, different resistance value) so I am
hopeful it may be just a matter of time.
6:36 p.m.
New subject: Looking for a potentiometer for restoration project
Out of curiosity, why do you think the pot is bad?
Wayne
Wayne,
I could be totally wrong here (EE definitely was not my major) but
1. Turning the pot does not change the brightness of the screen at all
2. Measuring the pot and adjusting it (i.e. turning the knob) gives me a constant
resistance reading. Doing the same thing with the volume pot gives me a range of
resistances as expected.
If my thinking is wrong or I should be doing another test I am open to hearing it.
-Ali
7:17 p.m.
New subject: Looking for a potentiometer for restoration project
Just for clarification, a pot has 3 tabs. Ohmeter measuring across the 2 ?end? tabs should
indicate the total resistance of the pot (10k, 50k, 500k ohms, whatever the schematic
says). If the measurement is infinite then the potentiometer is open broken. If you get
that reading, you might want to open one end of the pot and remeasure just to be sure.
If it measures close to the schematic value then measure one of the ends and the center
tab and rotating the potentiometer should show different values as it?s rotated. Also
measure the other side to the center and see if the values change in the other direction.
Potentiometers are just an exposed piece of carbon ( or wirewound) with a wiper blade (the
center tab) going across it. Sometimes the solid piece of carbon can break causing the
open condition, but still providing somewhat variable resistance.
It?s been my experience in repairing televisions that the brightness control rarely goes
bad it?s usually some other component in the brightness circuit and a lot of times it?s
just an aging CRT.
I wasn?t able to see the pictures because you need to be a member of vcf.
Sent from my iPhone
On Jan 19, 2021, at 15:36, Ali <cctalk at
ibm51xx.net> wrote:
?
Out of curiosity, why do you think the pot is bad?
Wayne
Wayne,
I could be totally wrong here (EE definitely was not my major) but
1. Turning the pot does not change the brightness of the screen at all
2. Measuring the pot and adjusting it (i.e. turning the knob) gives me a constant
resistance reading. Doing the same thing with the volume pot gives me a range of
resistances as expected.
If my thinking is wrong or I should be doing another test I am open to hearing it.
-Ali
20 Jan
20 Jan
3:38 a.m.
For a workaround:
This way You get a fixed brightness and somewhat working computer.
Now You can wait for a replacement pot and play with the computer.
So turns out the pot itself is good after further testing. Of course now the
question is why won't the brightness adjust on the machine?
-Ali
1284
days inactive
1285
days old
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