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tiff_lee

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Ok so the Rave Racer cab I just picked up has some CRT issues, so apart from the obvious get the chassis serviced I think I have some issues outside of that (although possibly not)

The CRT is a Pentranic A79PNT25X, I can't find any identifying marks on the chassis i'll need to take a better look but the neck board has RODO JW07, Rodotron? There is a remote board for all adjustments bar R/G/B gain behind the dashboard.

Few observations so far
  • The brightness was cranked right up on the monitor and turning it down to 'normal' levels results in the image starting to fade away on the left and ultimately just (raster?) lines across the screen
  • The pics don't show it but the image doesn't look level across the screen, like it is slanted almost.
  • Appears to be some vertical black lines across the image
  • Unable to reduce horizontal width sufficiently (assumed this to be a chassis/servicing issue)

Just realised some of my pics are garbage but here's a couple to get me started.

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The Pentratonic monitors I've encountered have had Rodotron chassis.

Turn down the voltage on the screen pot on the flyback. That will sort out the raster lines and the overblown brightness.

It's a 20 year old chassis with most likely low quality caps, so a cap kit is definitely in order.
 
Yeah low quality at time of build 20 years ago! ><

I'll be hitting Jomac up soon to get a quote, i'm gonna have like at least a dozen chassis I wanna get serviced
 
Obviously not a bad bit of kit since it is still running. With a recap it could go for a long while yet.
 
Got this chassis back from Jomac in his own words "it was a mess", he pointed out marks on the rear of the anode cap that he said was caused by arcing from the tube being dirty (and it was filthy) there is also marks on the actual rear of the tube as well (shown after cleaning the immediate area).

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Need to spend some more time setting the monitor up but there still one problem remaining and that is the image isn't level across the screen (as it was before the service). The right hand side is higher than the left resulting in a slanted image as it does across the screen, what could cause this?

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You need to rotate the deflection yoke.

However, more than likely the yoke is glued to the wedges holding it in place. Rotating means that you will have to separate it from the wedges or the wedges from the tube. If the yoke tilts during this point, geometry can turn to shit.

If you're going to attempt this, you need to do it while the monitor is on. Remember to undo the clamp at the base of the yoke, and don't touch the poles on top of the yoke.
 
Cheers Nem, good to know it can be sorted I think ill just leave that one for a rainy day though after some more self education on such a task!
 
Sort out the linearity on the right hand side first.. The squares should be almost the same size all over the monitor (except the multiple lines near the center/middle). On the right hand side they look like bricks instead of squares.
 
Sort out the linearity on the right hand side first.. The squares should be almost the same size all over the monitor (except the multiple lines near the center/middle). On the right hand side they look like bricks instead of squares.
I don't think there's any way to sort it. @tiff_lee, you could ask Jomac if he knows of any way to fix it. I'm sure he knows these chassis inside out.

Honestly, it's not even that bad. In a racing game you probably won't even notice it.
 
Oh right yeah I never actually noticed those squares on the far right! I'll take a look but i'm pretty sure if I try adjusting that i'm just going to make all the other squares more rectangular (H width?).

Nem you are right I didn't even notice in game although i'll probably not be able to unsee this now, it was the slanted image that was doing my head in but again once in game you don't really notice it when focusing on the racing.
 
Your width is spot on, adjusting that won't make a lick of difference. Some chassis have a separate pot for horizontal linearity, however, it usually affects linearity in the center of the tube, not on the edge. Your chassis most likely doesn't even have one.

On a newer Rodotron you can fix side compression by changing one cap:

https://wiki.arcadeotaku.com/w/Rodotron_666#Side_Compression_in_15KHz

Yours could be similar, since it's most likely a dual sync chassis. Jomac might know.
 
Oh good link and interesting stuff.

Yeah i'm sure Jomac will be happy to offer some advice seeing as I took it to him for servicing.
 
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