30Khz -> 15Khz monitor briefly: big deal?!

[rampy]

Q: Old School VGA to ArcMon hack

There was once a time, before the dawn of the ArcadeVGA card where your only option (ok there are scan converters too, or jpac and special trident card, stay with me here) to interface a PC to an arcade monitor was to do a VGA cable hack and use ArcadeOS and/or a TSR like ArcMon+ or the like.

I've re-read the PCJAMMA site recently, and have this question:

How do people deal with the BIOS bootup screen before the TSR/ArcadeOS can "hook" into the card and force the 15khz modes? i.e. the wait for the all clear 3 beeps?

Are you building those circuits from the PC2Jamma site?

Are you doing it manually, i.e. power up PC, then flick on Arcade Monitor PowerSupply a few seconds later?

Are you saying screw it, and starting both at the same time, 5 seconds of 30khz to an arcade monitor be damned!?? (and did you do this more than once?)

Are there other circuits/tricks/philosphies?

The ArcadeVGA card is a relatively new evolution in our hobby, so I figure there's got to be some people who've done it the old skool way before.

I've already got a voodoo3 that should work well with arcadeOS/arc mon plus , and am trying to do a project on the cheap using my leftovers for a buddy of mine.

Your thoughts, insights, and experience are appreciated.

Rampy

PS and yes I did check the FAQ =P

EDIT -> found this thread from way back by Frosty Neuromancer seems to imply brief, high frequencies burst haven't hurt his monitor (or did it? ) =P

EDIT2 -> OK, i've looked through EVERY post that mentioned Arcade Monitor in the Monitor forum going back to the beginning (well nearly all of them) and have not really found an answer =(

What happens when you send 30khz signal to a CGA/standard res arcade monitor for 5 second intervals?

[MameFan]

I'll try to provide some input, though I am not totally up on VGA monitor design/signal issues.

First, my gut says "avoid it".  Why?  I remember back about 10 years ago when I started at my current company and we all had crappy Packard Bell or somewhat better Relisys VGA monitors, and a few "nice-pricy" NEC's.  Most 640x480 some 800x600.   We got in a batch of new computers with new video cards, but no new monitors. By default they ran 56 or 60hz and nothing else if memory servers.   The new cards defaulted to 72 hz.   After everyone started connecting up their new computers and getting into windows and installing the new drivers, we started smelling things...  Yep... suddenly numerous monitors were literally smoking from their backs due to the sync mis-match.

Therefore that lesson said running 72 hz [vertical] (and whatever the related KHz horizontal divides out to be) into a monitor designed for less was definitely a BAD BAD thing.

That said, a couple years later, Multisync was all the thing and the possibility of "frying" a VGA monitor with too high (or low) of sync was very rare, even if you left it so that you had no horizontal hold due to too high of a scan rate.


But if we go back to arcade monitors... at least the original chassis (and probably replacement chassis that ASSUME only 1 sync frequency) then you may assume that they were never meant to handle such a high rate and may have components fail when fed too much.  

But it could also be that they were made to support bad connections/dead boards that put out bad signals and simply ignore or not fail with too high of scan rates.

I guess a good question would be to ask any ops that ever connected up medium res (EGA--640x350 instead of CGA--320x200) games to an old standard res monitor and what happened, other than no sync?


As far as how to "automate" this...  My only thinking here is you could consruct a simply analog switch device attached to a timing chip.  As soon as it gets power, you could have it count to 5 or so seconds then switch the sync signal in and then you'd be set.

LMK if you'd like to have me try to hunt down the TTL chip numbers and draw up a circuit if you're serious about this option....  I've never built it, but know it can be with a counter and an analog switch pretty easily based upon my electronics knowlege.


Hopefully this helped some. LMK if you need anything else... Sorry I can't "for sure" answer your question... I'm only working on speculation and erroring on the side of caution.

[rampy]

Thanks MameFan,

That's a good way to approach the operators without using the dirty word of "mame" in front of them.

Thanks, also for offer for circuit design...  on the PC2Jamma There are 2 basic designs ( they use the parallel port to trigger either an relay to switch the AC power to the monitor when it is "safe" or a switching chip to turn on/off the VGA signal when it's safe)  link to section of pc2jamma  (hit next at the bottom for the following pages)

Those are reasonable breadboard projects for me to undertake, but I wonder if they are necessary.  

If I was going to that trouble, I'd rather build something akin to the jpac's arcade monitor protection circuit that clamps/halves anything over 15khz ...  (why not use a j-pac ?  what if you didn't have a Jamma/harness cabinet, or were using a different encoder? --> see my dilemna?)

*shrug*  I gotta figure some of you guys have dealt with this before (even if you blew your monitors in the process =P )

Like I kinda wonder if the "warm up" time of the monitor would be sufficient to skip it over the bios/boot screen VGA frequencies.  (that doesn't handle warm reboots though =(  )

So, yeah... still looking for some practical examples of this situation...

Rampy

[MameFan]

> "Like I kinda wonder if the "warm up" time of the monitor would be sufficient to skip it over the bios/boot screen VGA frequencies.  (that doesn't handle warm reboots though =(  )"

The "warm up" of a monitor is primarily in the CRT itself needing to start cooking at the high voltages its fed.  The rest of the circuitry, especially the lower voltage stuff where the deflection is done, IS up and running virtually immediately after power on.  Therefore too high of a scan rate will actually ruin either the electronics (most likely IF they ruin something) or the copper windings in the yoke (less likely) ... Nothing about scan rate will affect the tube itself, which is the last thing to get up to full power anyway.

[tom61]

You will not want to run an arcade monitor at 31kHz, for the sake of your ears if nothing else. Makes a really high screaching noise. Anything that makes noises like that can't be good for the monitor. Most arcade monitors don't have sync protection circuitry, so it can damage the circuitry.

This is why the J-Pac has sync protection circuitry (if I remember right the first versions of it, it lacked the 'sync splitter', and just had the protection)

[AndyWarne]

I think it is true to say that all currently produced monitors have sync protection BUT please don't try it just to prove me right (or wrong!). Older monitors definitely do not like being driven at a higher rate. The flyback transformer produces an output voltage which increases as the frequency increases, so with double the correct rate the voltage is enough to immediately burn up the windings.
If you are into soldering/breadboarding etc I can supply the microcontroller from the J-PAC and pinouts, so you could build the circuit.

[rampy]

Thank you Andy,

The project is currently in a "prototyping" stage (i.e. half arse see if it'll work hacks)

It turns out the cabinet in question does have a jamma harness, but it seems that the video doesn't seemed to be currently routed through it (i've got to do a little bit better wire tracing to determine where the jamma leads that are supposed to be for video end up =P but it's difficult when they are all bundled togethr and have changed color with age/dust)

long story short -> I'm sure after the hobble it together to see if it works phase is over my friend (the benefactor of this project) will be able to spring for either a  JPAC or an arcadeVGA and ipac...

Everythings pretty much in flux right now (as to which direction the project will take) and i've got much to learn about arcade monitors now that i've stared one down for a wihile.  

Thanks again Andy, Tom, and Mamefan for your advise/thoughts and circuit help, but it looks like I may end up on the road more traveled afterall (at some point)

Rampy
PS it was good to finally get a definitive answer though, as I hadn't seen a "clear" answer to corroberate with the pc2jamma site info...!
 

[planetjay]

To Andy: So it's a microcontroller. I wondered how you did that.

To Rampster: The offer to build it for you stands.

To Me: Have you lost your mind?

[AlanS17]

I would suggest getting a video amplifier from the ultimarc website. The new ones input a vga connection and output the proper wiring for the monitor.

I know the J-Pac includes circuitry to block offending frequencies, but I'm not sure the video aplifier does or not. However, it says "The circuitry is exactly the same as that used on the J-PAC and uses a high-bandwidth video amplifier chip."

You may want to ask Andy about it. At $15 it seems a good solution.

[rampy]

I would suggest getting a video amplifier from the ultimarc website. The new ones input a vga connection and output the proper wiring for the monitor.

I know the J-Pac includes circuitry to block offending frequencies, but I'm not sure the video aplifier does or not. However, it says "The circuitry is exactly the same as that used on the J-PAC and uses a high-bandwidth video amplifier chip."

You may want to ask Andy about it. At $15 it seems a good solution.

I wonder too now... but I wouldn't think so, or Andy would have recommended it.

I believe the WG monitor (WG19K4675)  I'm using is perfectly content with the 1volt emmited from the video card so that's a bonus that I most likely don't *neeD* the video amp (one of my concerns going into this)  but I may still need some sync protection.

Thank you again PJ, I appreciate the offer, and am sure you could build a much cleaner circuit that I, but I am capable of breadboarding (badly =P)

I do wish I bought the pre-hacked VGA cable from ultimarc though, that was a pain in the butt (and I want to redo it with heat shrink to help it be more secure)

*Shrug* thanks again all!

Rampy