TG16 RGB works w/HDMI Converter but not GBS-8200

[SmokeMonster]

I installed broken's RGB amp in a TG16 and the picture is beautiful on my generic Scart-to-HDMI converter, but I get no video output at all on a Gonbes GBS-8200 w/LM1881 sync stripper. This thread documents how my GBS is set up.

Is anyone using a TG16 & GBS-8200 w/LM1881 successfully? At first I thought this was an issue with the scart cable that I was using, but today I wired up a custom cable specifically for the TG16 and the result is the same.

[thesteve]

i tried 1 and got a pic
wasnt a good pic

[SmokeMonster]

Thanks for the response but I'm not sure what you mean. The picture quality was bad, or the signal itself? Were you running the composite sync through an LM1881?

[SignOfZeta]

I gave up on getting these two fuckers to cooperate. My GBS locks onto a SNES or a JAMMA board like magic, but can barely grab a single frame from a PCE. I built multiple amps and sync stripper setups and eventually just gave up.

[Fidde_se]

I looked into this and couple months ago, if I remember correctly it had something to do with needed to be scandoubled first, but hey SNES is also 240p....

They sell things on arcade forge to make that work apparently and a super setup with everything that's also suppose to work,  then there's the guy on youtube that explains how to build some circuit for the pce to make it work.

[thesteve]

i tried it using a LM1881 and also as component
the issue was poor signal lock, wont maintain video
didnt matter how i processed the signal first

[SignOfZeta]

I looked into this and couple months ago, if I remember correctly it had something to do with needed to be scandoubled first, but hey SNES is also 240p....

Since this thing was designed for arcade boards that solution makes no sense.

[Fidde_se]

I know... The specs says 480i as lowest.

[Fidde_se]

Heard this is supposed to work...
http://arcadeforge.net/SLG-in-a-Box/SLG-in-a-Box::71.html

[SmokeMonster]

My GBS-8200 works great with SNES, Genesis/32X, and Saturn. I have now seen videos of it working with PC Engines, but I can't find any info on how it was accomplished.

This almost certainly has to be a sync issue, since the RGB lines are all perfectly set using broken's amp. Is there a good way to boost or prepare the composite signal before it's output to the LM1881?

I tested the composite output straight off of the hu6260 chip, but found that it is actually a very weak c-sync line which doesn't suit either my cheap HDMI converter or the GBS.

[Fidde_se]

If it would be the sync use the LM1881 and then the sync amp after that
http://www.gamesx.com/grafx/pce_rgb.jpg
(lower right only)

[SmokeMonster]

If it would be the sync use the LM1881 and then the sync amp after that

(lower right only)

Thank you for the link. I have all of the parts to build this. Could it be used to boost the composite video before sending it to the LM1881?

I would be worried about boosting the LM1881's sync output because Ian Stedman found that it already outputs too high of a voltage for the GBS. The LM1881 outputs 4-5v sync, while the GBS's TVIA-5725 chip accepts a maximum of 3.6v. This can be corrected by adding a 680 ohm resistor to the sync output from the LM1881. When the LM1881's sync is attached straight to the GBS without a resistor, it activates the chip's ESD protection and could cause damage in the long term.

[SmokeMonster]

I built the amp and tried it on both the composite video and c-sync. Neither worked. I also added a SPDT sliding switch to my GBS, to bypass the LM1881 altogether. This also made no difference.

update: I also tried tapping luma straight from the hu6260 to the LM1881 (it should be able to extract c-sync from luma or composite). The screen goes black, but then nothing.

[Fidde_se]

Ok if you even suspect there's something wrong with the sync, use another sync...
use a SNES (NTSC) sync, cleaned is preferred.

The sync is not something magical, it's just an index pulse, for tv stations and cutting studios they all have a master sync in the basement so that all inhouse monitors changes frames at the exact same time, you could even build your own sync using a LM555 circuit and place inside a console.

A PAL sync would work but would give a very choppy frameskipping picture.

http://www.retrosampling.se/Temp/PCE_RGB_SCART/Scart%20Connector%20with%20Sync%20Comp%20Switch.jpg

[SmokeMonster]

Sync might not be magical, but the GBS is very particular about the sync signals that it will accept.

Using a SNES sync doesn't offer the solution that I'm looking for, and I'm trying to figure this out so everyone with a GBS will be able use it with their TG/PCE.

Also, the LM555 doesn't look like it could be used to create the proper sync signal, and I couldn't find any evidence that anyone has ever used it to do so. Is that just a theory or have you actually used it in this way?

[Fidde_se]

Using a SNES was just to test it with a known working sync, LM555 is the worlds most common timer circuit, I use it for dreamcast fans all the time, probably any kind of sync/pulse signal for these kind of purposes can built with it, creating that kind of signals is it's only function.

Still it needs 480i as minimum so I would guess there's where the problem really lies.

[SmokeMonster]

I see, I'll give the SNES sync a test the next time that I have the TG setup for testing. Thanks for the suggestion.

It can't be the 480i issue because the GBS works with SNES, Genesis, Amigas, N64, Saturn, as well as with arcade boards (MVS, AES, etc). All of these systems output 240p. It interprets them as 480i, which is problematic, but they are all able to be converted relatively well.

[SignOfZeta]

Yeah, I've had several systems hooked to the GBS and aside from flicker effects not working perfectly the image was rock solid perfect. IIRC, Saturn was with a dedicated sync and a home made cable, , SNES had composite sync, JAMMA was dedicated sync (right off the edge). I think I did Mega Drive but I can't remember.

It was never designed to with with composite sync, I don't think, but the SNES has just about the best composite of any system, maybe that helped?

[HercTNT]

I have a GBS-8200 hooked up to a Pcengine Duo-r and have no issues with it. I had to build a sync stripper to stabalize the picture. Professorprofessorson helped me simplify  the circuit. Unlike what others are reporting, I found the picture to be vibrant and look great. Its possible success may depend on the type of rgb mod done. Some cables have sync strippers and amps built into them. If your duo is already amped, it could screw up the signal. Also, the GbS-8200 really needs a power supply that delivers at least 2 amps to operate correctly. they can be finicky and any less than 2amps might cause issue.

[thesteve]

i didnt try too hard, as i have RGB capability

[HercTNT]

i didnt try too hard, as i have RGB capability

I did not mean that as a slight, I just meant that everyone might have different setups. I just know that the rgb mod i have, combined with the sync stripper and the gbs, work damn near flawless. Zeta mentioned the occasional tear in the screen. I have seen that from time to time on my setup as well but its very rare.

[thesteve]

I didn't take offense to it
I was using it on a neo mvs and decided to try it on PCE, just because it was handy, and to see if the tearing issue I was having was the GBS8200 or the neo
The PCE did even worse
My puck man board however is perfect on it
I tried RGBS using the 1881 and component using the latest board with the same results
I suspect it has more to do with the software on the 8200

[SignOfZeta]

I tried every readily available amp circuit I could find on the net. I probably built 4 different circuits trying to get this bitch to sync. The PCE itself looked great on an actual analog RGB monitor, worked with XRGB2+ perfectly as well, would grab about one frame a minute on the GBS. That combo defeated me totally.

[Fidde_se]

While it works flawlessly on TV's with RGB Scart and PVM's, both with and without an amp, yes very dark with the latter...

It seems just to be the converters that are struggling, so if it's not the sync that gives a hard time it has to be the signal and different amps and their circuit solutions that has different output impedance, that's the best clue I can give...

[SignOfZeta]

It seems to need a time base corrector, if anything.

[HercTNT]

Stupid question, but do you have the gbs-8200 or 8220? There is a slight difference between them that could be a problem.

http://www.theisozone.com/forum/viewtopic.php?f=20&t=47226

http://www.neo-geo.com/forums/showthread.php?243158-GBS-8200-amp-LM1881-help

These two links have possible fixes. It seems with some of these units replacing the caps is essential to vastly improved quality.

[SmokeMonster]

Stupid question, but do you have the gbs-8200 or 8220? There is a slight difference between them that could be a problem.

http://www.theisozone.com/forum/viewtopic.php?f=20&t=47226

http://www.neo-geo.com/forums/showthread.php?243158-GBS-8200-amp-LM1881-help

These two links have possible fixes. It seems with some of these units replacing the caps is essential to vastly improved quality.

I have the 8200. I wrote and maintain the first guide that you linked above

[HercTNT]

Stupid question, but do you have the gbs-8200 or 8220? There is a slight difference between them that could be a problem.

http://www.theisozone.com/forum/viewtopic.php?f=20&t=47226

http://www.neo-geo.com/forums/showthread.php?243158-GBS-8200-amp-LM1881-help

These two links have possible fixes. It seems with some of these units replacing the caps is essential to vastly improved quality.

I have the 8200. I wrote and maintain the first guide that you linked above

well, I feel dumb. Did not notice that.

[SmokeMonster]

well, I feel dumb. Did not notice that.

No, I'm glad you found it. Hopefully that means others will find it useful too