Pentranic 1125 25" monitor. ***FIXED...For real!***

[Mauzy]

Ive done a lot of research and I can't seem to find any info on the Pentranic 1125, let alone a cap kit for it. Bob Roberts has a kit for the 1025 25" monitor, but no 1125. They aren't the same are they? Pentranic's site acts as though their pre-2000 products never existed. Must be because of the corporate shake up...

So I capped this monitor this evening, and it looks pretty good with the following exceptions:
1. There is a slight "jitter" throughout the picture, not bad cap squiggle, but bad adjustment squiggle.
2. Squeal that seems to be related to brightness or contrast.

The only way to get rid of the squeal is to crank up the screen control and brightness pot ALL the way up. It gets louder as the screen gets darker.

The squiggle looks like a 50/60 hz maladjustment, but I can't find that particular control on my CH-288 chassis.

I have already reflowed all of the solder joints on the caps I replaced.

[grantspain]

do you have a photo of the chassis?

[Mauzy]

I just looked at it and it is for sure an 1125. Do you still need pictures?

[grantspain]

I just looked at it and it is for sure an 1125. Do you still need pictures?

yes because pentranic just rebranded other chassis so it may be a rodotron

[Mauzy]

Oh I see. Here you go. Hopefully the clickable-ness works out on these.

[Ken Layton]

1125 should be a CH888a chassis:

http://www.alsmarketing.net/CH-888A-specsRev1.pdf

[Rickn]

No it is a CH288 chassis we use this board in our standard res line-up. You can find the schematic here

http://niemandisplays.com/nvd%20ch-288%20cga%20only.pdf

Good luck

Rick Nieman
Rick@niemandisplays.com
www.niemandisplays.com

[Mauzy]

No it is a CH288 chassis we use this board in our standard res line-up. You can find the schematic here

http://niemandisplays.com/nvd%20ch-288%20cga%20only.pdf

Good luck

Rick Nieman
Rick@niemandisplays.com
www.niemandisplays.com

Wow. Thats one the most easy to understand schematic sheets I've seen. I can actually read that. Is this your guys' doing?

I do have a question as to the notation: on a cap sympbol, it has a number - slash - number, like this : 1/50. that is 1uf (I dont know how to make the micro symbol...) 50 volt, correct?

[Ken Layton]

Yes, that would be 1 uf @ 50 volts.

[Mauzy]

So I capped this monitor this evening, and it looks pretty good with the following exceptions:
1. There is a slight "jitter" throughout the picture, not bad cap squiggle, but bad adjustment squiggle.
2. Squeal that seems to be related to brightness or contrast.

The only way to get rid of the squeal is to crank up the screen control and brightness pot ALL the way up. It gets louder as the screen gets darker.

The squiggle looks like a 50/60 hz maladjustment, but I can't find that particular control on my CH-288 chassis.

I have already reflowed all of the solder joints on the caps I replaced.

[grantspain]

maybe a slightly unstable b+

[Mauzy]

Would that account for both problems?

For some reason, I am unable to find a B+ adjustment both on board and on the schematic. Would it have a different name?



Heres te schematic:
http://niemandisplays.com/nvd%20ch-288%20cga%20only.pdf

[grantspain]

looks like the b+ is not adjustable,when i meant unstable i was referring to a smoothing problem on the b+ rather than adjustment
look like the b+ should be 123 volts perhaps you can measure it to be sure

[Mauzy]

Something I've been meaning to ask for about two years: where would I look to measure that?

I noticed you said something about smoothing: isn't there a such thing as a smoothing cap?

[Kevin Mullins]

...

[Mauzy]

oh. nice catch.

can't explain that one. 

[Kevin Mullins]

Couple other things I spotted in your pics.

[Mauzy]

alright, alright I get it...

In my defense I wasn't the only one who missed that CH-288 marking in this thread...

[Kevin Mullins]

Just taking notes is all.....

 

[Mauzy]

Of course 

Wait: were you trying to show an adjustment or a place to measure from? I thought you were trying to show an adjustment (there is no pot there), but it just hit me that I could measure there. 

That point is in the least accessible place while the monitor is running...

EDIT: I looked at measuring at that point, but the positive and negative are bridged (duh). How can this be measured?

[Mauzy]

I think I have it fixed. the problem was directly related to brightness, even though the picture (color, brightness, etc) looked fine, it was shaking slightly back and forth. If the picture was at a"normal" brightness setting, it would squeal and shake. If you cranked the brightness all the way up, it would stabilize and be quiet. After adjusting the sub-brightness on the neck card, the screen control, and the external adjustment board, its stable and not squealing, though it is a little washed out. It took about 2 hours of running back and forth between the three pots, but I think I got it...

EDIT:  I had to adjust the color drives, and found that this will also throw it into a fit. I have it adjusted to where the symptoms only come up on random screens. Its running Golden Tee 2K. For example (this doesn't always work. sometimes screens that are usually good come up bad and vice versa) the main title screen may come up fine, relatively quiet monitor (no squeal, just "powered on" hum) no waviness. It will switch screens into, say, the high score screen and that will squeal and shake like before. Then it could go into a demo and be perfectly fine. Like I said, its not always the same screens.




When you hear the squeal - its wavy. When you hear silence - perfect picture. Disregard the end showing the screen, was trying to catch it waving - it wasnt.

[Mauzy]

Okay. After doing a little research on filter capacitors, let me get my facts straight for a second. A filter capacitor corrects any stray AC voltage going into a DC linear transformer. If the capacitor loses capacitance, some of the AC ripple is allowed into the transformer which will cause a sound (which I have) and further power issues.

Does this sound right? If so, how do I determine which capacitor is the filter capacitor? Should it be the largest right off of the linear transformer?

[qrz]

also check c309, c512 ( 1uF/50v) and c165 ( 47uf/35)
might want to sub an her508 for d501 (30df6)

the her508 has a faster rcovery time - 50ns versus 400ns

qrz

[Mauzy]

the her508 has a faster rcovery time - 50ns versus 400ns

qrz

recovery time?


Anyhow, I reflowed those joints and fixed a lifted pad on the auxiliary board and all seems to be good! Thanks to all for the advice (and mocking  )! This thing looks great!

[Kevin Mullins]

Awesome !!

Always good to hear the outcomes and solutions.