Pentranic CH-288 - Geometry issue. Narrow image on borders

[Mendion]

Hi everybody.

I need some help on trying to fix a geometry issue I'm having on my arcade monitor:

Chassis: Pentranic CH-288
Monitor: Pentranic A68PNT18X Dual resolution monitor CGA/EGA

Here is an image of a Dot Cross Hatch on this monitor:


And here is a video of Super Street Fighter 2 on this monitor:




As you can see, the image is completely distorted on the borders. It gets really narrow.
I've played with all the image control pots for horizontal and I can widen and narrow the image, but the image on the sides is always distorted.


I've already replaced all electrolytic capacitors of the chassis with a new cap kit I purchased. After the cap kit replacement, nothing changed, the behavior is the same! 

There is only 1 capacitor I did not replace because I'm a little confused about that one. It's C907. The cap kit came with a 4.7uF 100V cap (that is a very very small cap). Specs sheet tells that one is a 4.7uF 75V. So we are good there.
The thing is on my chassis I have a pretty BIG capacitor there that is an 8.2uF 200V??? It's this one:




This chassis has some pretty ugly jobs done in the past. Awful soldering work and I'm afraid whoever touched this thing put whatever capacitor he had at hand to keep the thing working in some way...

The thing is I don't know if that cap has some relation to the geometry issue I'm having or If I have to look somewhere else.


Any help will be much appreciated.

Thanks!

[grantspain]

is this a recent fault?

[Mendion]

is this a recent fault?

I don't know. I bought it really cheap with this issue...

[grantspain]

it could be a bad poly cap in the horizontal deflection, it could be that the chassis is not matched to that tube/deflection coil. Is the horizontal size pot working?
the issue is horizontal linearity btw

[Mendion]

it could be a bad poly cap in the horizontal deflection, it could be that the chassis is not matched to that tube/deflection coil. Is the horizontal size pot working?
the issue is horizontal linearity btw

Yep. All the pots are working. I've put a video on YouTube to show how the pots are working right now:




Do you know which poly cap is responsible for the horizontal linearity? should I replace that one?

[lilshawn]

commenting becasue i have a 2400 series troubleshooting cheat sheet written on the back of the schematic from working on these over the years. i'll take a look at it at work tomorrow.

EDIT: most of it is in the thread...

http://forum.arcadecontrols.com/index.php/topic,99948.msg1059036.html#msg1059036

[Mendion]

commenting becasue i have a 2400 series troubleshooting cheat sheet written on the back of the schematic from working on these over the years. i'll take a look at it at work tomorrow.

EDIT: most of it is in the thread...

http://forum.arcadecontrols.com/index.php/topic,99948.msg1059036.html#msg1059036

Thanks for the info. But you have a Makvision 2425.

I know Makvision and Pentranic chassis are related in some way (or are the same brand? not sure). Is the Makvision 2425 the same chassis as the Pentranic CH-288?.

What conclusions can I get from the info Rickn posted on your thread?. Sorry but I'm not understanding.

[lilshawn]

all the chassis are clones of each other. makvision, petranic, weiya... all the same. it's common to call all the chassis the 2400 series. the 2400 chassis is basically a pentranic branded Wei-ya chassis (CH-288) pentranic later became? Makvision...spun off anyways.

Rickn was the engineer for pentranic...later Makvision (I think)... later still... spun off his own business Nieman video displays. (still using wei-ya chassis like the CH-666)

TL;DR - all the same.

[Mendion]

all the chassis are clones of each other. makvision, petranic, weiya... all the same. it's common to call all the chassis the 2400 series. the 2400 chassis is basically a pentranic branded Wei-ya chassis (CH-288) pentranic later became? Makvision...spun off anyways.

Rickn was the engineer for pentranic...later Makvision (I think)... later still... spun off his own business Nieman video displays. (still using wei-ya chassis like the CH-666)

TL;DR - all the same.

Ok, that is good to know!

Now, regarding my issue with this specific chassis, I still have not clear which cap is the culprit here. I can't figure it out with the info Rickn posted on your topic...

[lilshawn]

there is a capacitor used for tuning it's over by the DIP IC HA11235??. I'd have to look at my notes. (sorry i didn't get a chance to look at my notes today, and I'm out of town tomorrow doing a jukebox install.)

is this chassis always bee with this tube... did it work before and now doesn't? I ask because this chassis was used for several different tubes and gets configured differently for each one. if someone has swapped the chassis, it might need some parts changed to work properly.

[Mendion]

there is a capacitor used for tuning it's over by the DIP IC HA11235??. I'd have to look at my notes. (sorry i didn't get a chance to look at my notes today, and I'm out of town tomorrow doing a jukebox install.)

is this chassis always bee with this tube... did it work before and now doesn't? I ask because this chassis was used for several different tubes and gets configured differently for each one. if someone has swapped the chassis, it might need some parts changed to work properly.

I'm not sure. I recently purchased this cabinet. I'm not the original owner. But, for what I saw, I'm pretty confident this is the original chassis of this cabinet. I also believe the tube it's the original one. I have a friend of mine that has 2 of the same cabinets (It's a WECHE OK Baby) and both has the same chassis and tube as mine.

Whenever you have the chance to look at your notes regarding this chassis, please, share them here. I will really appreciate that.
Thanks for your help!

[lilshawn]

okay, I just ask because it's not uncommon for operators to swap chassis to get cabs going but not knowing that a 33" cab chassis, although will work with a 27, will have all sorts of screen distortions. (chassis can be used with 25,27 and 30 inch tubes...all needing slight tweaks to work properly)

[lilshawn]

For geometry issues and width I have noted...

Remove R904
C908 change to "224" (0.22uF)

And


Hphase issue - Change C306

As well as

Horizontal issues - change C394 and C912

[Mendion]

Ok, I've finally had the time to pull out the chasis again and take a look at C908, C908A and R904.

I didn't notice this before... WHAT IS GOING ON HERE???

I've took some pictures of the capacitors that are there. Can someone explain me why someone did that modification? What is the purpose of doing so?.










The values of the capacitors can be seen on the pictures.

On the Specs Sheet it says this:



So, in theory:
C908 should be a 334/250 (a 0.33 uF cap)
C908A should be, by the table there, a 394/250 (a 0.39 uF cap) - because I have a 29" tube

Now, actually, on my chassis:
The Brown one says .33uF, which is, if I'm not mistaken, the same as a 334 capacitor.
The Orange one confuses me... I can't figure out the actual value of that one!

R904 is intact.


I'm not sure what to do now. I need some input on how to proceed here because I don't understand which capacitors values should I put here or why someone bypassed the board traces by soldering this 2 caps together.

Grantspain? Lilshawn? Anyone else?


Thanks!

[lilshawn]

not uncommon to see scabmods like that. in this case, you would add the 2 values together. so possibly .22? (it does have a 22/k.......) and .33 so maybe it's at 0.55 total. the B81192 indicates it's a class x3 capacitor typically used for electromagnetic spike suppression in surge suppressors. someone could have scabbed it in there. hard to say.

i would start with dropping it to just the 0.33 (remove the yellow one) and see where you are at. if it's better, dump it down to 0.22 and see. if it's good, leave it.

[Mendion]

not uncommon to see scabmods like that. in this case, you would add the 2 values together. so possibly .22? (it does have a 22/k.......) and .33 so maybe it's at 0.55 total. the B81192 indicates it's a class x3 capacitor typically used for electromagnetic spike suppression in surge suppressors. someone could have scabbed it in there. hard to say.

i would start with dropping it to just the 0.33 (remove the yellow one) and see where you are at. if it's better, dump it down to 0.22 and see. if it's good, leave it.

OK! Will try that.


Question: Those caps were for the C908A. What about C908? There is NO CAP placed there.
On the spec sheet it says it has to be a 334/250 (0.33 uF).

What about that one?

[lilshawn]

typically you run with what's on the chassis. the schematic is more of a guideline. there are many MANY mods to these chassis to make them work with a multitude of tube/yoke combinations.  this section is one of them. this capacitor basically sets up the oscillation of the yoke.

high frequency is a real funky black magic voodoo type thing that tends to defy logic and universal constants...where at high enough frequencies putting a bend in a wire can cause a circuit to do wierd, unexpected and wonderful things. as you can see in the schematic addendum for the 908 cap... changing its value very little can have a huge effect on things. 0.47 to 0.39 to 0.33 for different tubes (with different scanning widths and deflection angles)

the cap value was suggested changing it to a lower value to essentially push the horizontal size smaller, so you could make more use of the H-size pot to stretch it out (stock value would have you almost have the h-size pot turned all the way almost to the stop and didn't give you much to play with.)

[Mendion]

OK, some good news!. I removed the .22uF cap (the orange one) and I left only the .33uF cap (the brown one).

Here is a photo:




I did a test and the image got A LOT thinner. And the best news is that is not distorted anymore on the borders! But using the pots to widen the screen is not enough to fill it completely. I assume 0.33uF is too low to accomplish that. Should I go with a 0.39uF like the spec sheet says?

Here is a video I made so you can appreciate better how was the result:

[grantspain]

check for width jumper, i am sure this chassis had them- they will be marked N and W

[Mendion]

check for width jumper, i am sure this chassis had them- they will be marked N and W

OK, I did a check and I can't found a jumper or connector. Only place I found a "N-W" marking is here, ans it's unpopulated:




Here you have a video I made showing the general section of where this "N-W" it's placed on the chassis. Hope you spot something that helps me.





In case there is no "N-W", does changing the C908A cap from 0.33uF to a bigger value help me in this case? Should I try something a little bit bigger, like a 0.39uF?

[lilshawn]

honestly, it really can't hurt to try experimenting with a few different values and see what you end up with.

[Mendion]

Well, now I'm REALLY confused.

I replaced the 0.33uF for a 0.39uF poly cap on C908A, and the image got a little bit thinner? (at least, that is what seems to me). See for yourself:








Let's go back to basics: What happens when you put a HIGHER cap value on the horizontal deflection? The image should get wider? or thinner?

What I'm not understanding is if while bigger the capacitance, the wider the image or if it is exactly the other way around

[lilshawn]

honestly, I don't recall. It's been awhile since I've messed with the tuning cap.

at least you are having fun and making progress. 

[Mendion]

honestly, I don't recall. It's been awhile since I've messed with the tuning cap.

at least you are having fun and making progress. 

I REALLY want to say I'm having fun, but...

The last time I had to remove the anode from the tube, one of the metallic hooks broke in half, I had to solder that back. It was a pain to do it. And that is going to broke again eventually if I have to remove the anode a few more times.

Since I'm not sure about how the value of the cap affects the width of the image, I'm going to buy a .22uF and a .47uF cap. I will start with the .22uF and if the image gets thinner, I will jump to the .47uF.

I don't have a better plan now...