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Author Topic: Monitor losing sync: JPAC or CRT_emudriver?  (Read 2353 times)

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big10p

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Monitor losing sync: JPAC or CRT_emudriver?
« on: December 03, 2016, 05:46:13 am »
Hi

I have an intermittent problem on one of my cabs. Sometimes, the monitor image becomes completely garbled due to loss of sync. The sync light on the JPAC goes out. This generally happens a few minutes after booting. Sometimes it'll happen when my front end is being displayed (interlaced mode), but I get sync back when launching a game. Sometimes it's the other way around where the front end displays fine, but games are garbled.

I suspect a faulty JPAC but wondered if it's possible my CRT_emudriver installation is faulty, somehow. I'm using win7 64 with CRT_emudriver 2.0. Anyone else experienced this problem? I haven't included logs as most of the time it works fine, so can't be a setup issue.

Cheers.

brad808

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #1 on: December 04, 2016, 10:40:55 am »
You can bypass the sync filters on the j-pac while keeping the video amp. Remove all the jumpers from the front then solder a small blob between pins 13-14 on the back of the jpac. If you do this it may solve your issue, if not you can eliminate the jpac as the culprit.




big10p

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #2 on: December 04, 2016, 11:31:39 am »
Thanks for the info, brad808. Just to be clear, will doing this mean the JPAC will just directly pass-through any sync signal it gets? Bit worried about passing the 31khz signal to my arcade monitor at boot up.

Can I ask why you made this mod to your JPAC? Were you having the same sync issue as me?

brad808

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #3 on: December 04, 2016, 02:56:18 pm »
Thanks for the info, brad808. Just to be clear, will doing this mean the JPAC will just directly pass-through any sync signal it gets? Bit worried about passing the 31khz signal to my arcade monitor at boot up.

Can I ask why you made this mod to your JPAC? Were you having the same sync issue as me?

Yes it'll pass everything through. Don't be worried about sending a boot signal for the few seconds before windows drivers kick in, or install atom bios to card.

Yes I had problems with J-pac sync circuit, I've had 5 now and all exhibit the same behavior so now I do this mod before I even install them. The sync circuit can't swap between 15-24-15 repeatedly for multisync monitors and needs to power down in order to regain sync. This is a big problem while using groovymame with auto sync monitors.

Also I've had in the past many times j-pac "randomly" drops sync of a signal it is displaying perfectly fine before. I wrote andy about this and he mentioned some people have had issues with the sync circuit not being able to properly identify certain modelines based on the sync pulse width being too narrow.

It was a problem that plagued my systems for a couple of years before I discovered this will solve it and not a single problem since.



If you want to test the jpac as well next time it happens, unplug the usb and plug it back in, see if it regains sync.

big10p

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #4 on: December 04, 2016, 03:29:27 pm »
I do remember a while back when this happened, I unplugged the VGA cable and plugged it back in, then the JPAC got sync again. Thanks again.

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #5 on: December 08, 2016, 01:16:33 pm »
@brad808, thanks a lot for this mod. I'll be trying it as soon as I get my new solderer.
Important note: posts reporting GM issues without a log will be IGNORED.
Steps to create a log:
 - From command line, run: groovymame.exe -v romname >romname.txt
 - Attach resulting romname.txt file to your post, instead or pasting it.

CRT Emudriver, VMMaker & Arcade OSD downloads, documentation and discussion:  Eiusdemmodi

brad808

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #6 on: December 08, 2016, 02:03:12 pm »
@brad808, thanks a lot for this mod. I'll be trying it as soon as I get my new solderer.
Glad to help. If someone doesn't have a soldering iron they could likely accomplish this by simply modifying a VGA cable. Soldering is certainly going to be much easier and will take a fraction of the time. With soldering you also have the added benefit of easily being able to reverse the mod should you ever want to in the future. Should accomplish the same goal though. 6 one, half dozen the other.

keropi

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #7 on: December 08, 2016, 04:32:24 pm »
that sync ciurcuit sure is strange on the JPAC... I have 2 of them on POLO28" monitors and I want to cut-off completely anything non-15khz... it doesn't work though no matter where I install the jumpers, I always get for example the garbled boot screens until CRT_EmuDriver loads... 15K only or 15K with "31K mode" is the same garbled screen :\

Zipper

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #8 on: December 09, 2016, 11:00:17 am »
This is really interesting. I've had a couple of j-pacs that lose sync and unplugging / plugging the vga was the only way to fix it.
I mailed Andy about it, and he suggested removing the jumpers... but that didn't help (just a messed up signal).

If blobbing the syncs together works then i'll dig out the old jpac. Thanks very much!

Interestingly, I do have a jpac that is absolutely solid without any mods... so i think there's is a tolerance issue on some of the jpacs.

Oh - Edit  - i found this video I made for Andy back in Jan, and I assume you are all seeing the same thing: https://www.youtube.com/watch?v=8uWzKsWwe1g
« Last Edit: December 09, 2016, 11:10:23 am by Zipper »

brad808

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #9 on: December 09, 2016, 02:29:44 pm »
Yes the problem with just removing the jumpers is you lose comp sync. That's why you need to solder in order to regain it.

big10p

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #10 on: December 11, 2016, 05:00:54 am »
This is really interesting. I've had a couple of j-pacs that lose sync and unplugging / plugging the vga was the only way to fix it.
I mailed Andy about it, and he suggested removing the jumpers... but that didn't help (just a messed up signal).

If blobbing the syncs together works then i'll dig out the old jpac. Thanks very much!

Interestingly, I do have a jpac that is absolutely solid without any mods... so i think there's is a tolerance issue on some of the jpacs.

Oh - Edit  - i found this video I made for Andy back in Jan, and I assume you are all seeing the same thing: https://www.youtube.com/watch?v=8uWzKsWwe1g
I only get this issue with one J-PAC, too. My other cab - which has had a couple of J-PACs in it - is rock solid. Both cabs have the same monitor in them. I haven't had time to try out this mod yet, but will definitely give it a go!

big10p

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #11 on: January 20, 2017, 10:02:37 am »
Only just got round to doing this mod, as well as flashing the ATOM-15 BIOS (to be on the safe side). So far, so good - all seems to be working well. As my issue was intermittent, I will need to test for a few weeks. Will report back then...

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #12 on: June 04, 2018, 10:31:09 am »
I know it's ancient, but the "blob" fix just saved/fixed my cabinet!  Thank you for posting this!
Quote from: brad808link=topic=152488.msg1596613#msg1596613 date=1480866055
You can bypass the sync filters on the j-pac while keeping the video amp. Remove all the jumpers from the front then solder a small blob between pins 13-14 on the back of the jpac. If you do this it may solve your issue, if not you can eliminate the jpac as the culprit.





big10p

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #13 on: June 04, 2018, 10:34:58 am »
Yep. Great fix. Had no problems since. Do it to all my J-PACs now. Thanks again to brad808!  :applaud:

brad808

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #14 on: June 05, 2018, 02:41:33 pm »
No problem guys. Also do it to all my jpacs

krick

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Re: Monitor losing sync: JPAC or CRT_emudriver?
« Reply #15 on: June 29, 2018, 04:41:25 pm »
I have an old JPAC that I purchased back in February of 2004.  It's one of the ones with the PS/2 keyboard connector & passthrough.  It's been pretty reliable so far.  I wonder if the manufacturing quality has gone down on newer models.
Hantarex Polo 15KHz
Sapphire Radeon HD 7750 2GB (GCN)
GroovyMAME 0.197.017h_d3d9ex
CRT Emudriver & CRT Tools 2.0 beta 13 (Crimson 16.2.1 for GCN cards)
Windows 7 Home Premium 64-bit
Intel Core i7-4790K @ 4.8GHz
ASUS Z87M-PLUS Motherboard

  
 

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