Trying to convert a TV to an Arcade monitor; I need help. - Page 1
Forum section: electronics / beginners

author: DC Jack
author_rank: Contributor
timestamp: December 10, 2023, 11:52:40 pm
content: I'm stuck.I have a Golden Axe arcade cabinet that the previous owner converted to use an LCD TV. It's not pretty. It is the only arcade machine that I have and will ever likely to own. It's one of those "I would like to own one of these one day" type fantasies and ten year old me is freaking out right now. The game in intended to be used with a 19" inch CRT and I've managed to get my hands on a Sansui TVM1915. It's a 19 inch CRT TV of 2000 vintage that only has an RF input. I am trying to Hijack the OSD RGB signal from the Micom chip to the Chroma/Jungle chip. I can't find any datasheets for the two chips, or service manuals for the TV, Chassis, or Neck Board. I'm working completely blind right now.I've managed to find the RGB and Blanking pins on both QFP chips (Orion OEC3039B Micom, Sanyo LA76814B Chroma) but I have had no luck and no idea where to find the Sync signal. I'm hoping someone here someone recognizes the chassis and might be able to help.I'm also hoping I can simply inject the RGB signals from the Golden Axe arcade board directly to the output pins of the Orion Micom chip and pull the Blanking pin up/down (whichever it turns out to be).I've attached pictures.

author: Ian.M
author_rank: Super Contributor
timestamp: December 11, 2023, 12:24:12 am
content: That looks very much like a live chassis set, which explains why it doesn't have any inputs except the antenna, which goes through an isolating RF coupler. If you attempt to connect the arcade board or any other RGB source to this TV (via its jungle chip or elsewhere), it will short the mains supply through the arcade board, killing it, and possibly you as well.

author: vk6zgo
author_rank: Super Contributor
timestamp: December 11, 2023, 12:42:00 am
content: Another problem:-CRT type TV displays are raster displays, many video games are vector displays, which require a different type of deflection yoke & associated circuitry.If someone has modified the game to use with an LCD TV, & derived normal composite video to feed that, it is already a "bodge", but they have done most of the work for you.If they have used some other method, you are in strife.There were quite a number of later generation TVs with composite & in many cases, component, video inputs which may a better choice than the one you have.

author: wasedadoc
author_rank: Super Contributor
timestamp: December 11, 2023, 01:47:37 am
content: Yes, no sign of a transformer which would be have to be present to enable a baseband video connection to the board.

author: Andy Chee
author_rank: Super Contributor
timestamp: December 11, 2023, 05:57:16 am
content: How about getting a new board for the TV?

author: CaptDon
author_rank: Super Contributor
timestamp: December 11, 2023, 02:31:43 pm
content: How was the LCD monitor connected? RGB+Sync? RF? What is coming off the actual game board? A little more info would help. I seriously doubt you can 'parallel in' to the television's internal circuits and it appears to be a hot chassis so that ends the journey right there unless the television's line input goes through an isolation transformer.

author: DC Jack
author_rank: Contributor
timestamp: December 11, 2023, 08:20:41 pm
content: Quote from: CaptDon on December 11, 2023, 02:31:43 pmIt looks like you are right. I just checked it out and the RF tuner is the only isolated section of the board. Nuts. I guess I'm on the hunt for another 19" tv.Currently the LCD monitor is connected with a VGA cable to a board, and that board is fed the RGB Sync Ground connections from the game board.

author: Ian.M
author_rank: Super Contributor
timestamp: December 11, 2023, 08:40:34 pm
content: I'd bet the tuner isn't isolated. Only the antenna jack is. The isolator is in that cube between the antenna jack and the tuner can.Key clues to spotting a live chassis set:No A/V inputsEither no headphone jack or one fed from a small audio transformerNo switching transformer in the PSUNo isolation gap visible on the underside of the PCB round the mains section of the PSU.Continuity between the negative side of the main bridge rectifier and the tuner can'Chunky' bit (containing isolator) between the antenna jack and the tuner canNote that some chassis had a mains live line output stage (also the horizontal scan coils on the yoke were live) but the rest of the board was not live. e.g. see the Salora Ipsalo 2:https://www.worldradiohistory.com/hd2/IDX-UK/Technology/Technology-All-Eras/Archive-Practical-Television-IDX/80s/Television-Servicing-UK-1984-09-OCR-Page-0012.pdf

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 11, 2023, 09:00:04 pm
content: Found that it uses TM8411B chassis, this document has schematics containing OEC3039B and LA76814M , the board looks identical.Schematic / boardview at pages 15-19.LA76814 datasheet.

author: CaptDon
author_rank: Super Contributor
timestamp: December 11, 2023, 09:01:03 pm
content: I would check the local GoodWill second hand stores for another 19" TV/Monitor with the VGA capability. I bought a nice one here in the states for $20 for our guest bedroom.

author: themadhippy
author_rank: Super Contributor
timestamp: December 11, 2023, 09:39:57 pm
content: another option is a rgb/scart-rf modulator.

author: DC Jack
author_rank: Contributor
timestamp: December 12, 2023, 01:25:59 am
content: Quote from: DavidAlfa on December 11, 2023, 09:00:04 pmThank you for trying, truly. Unfortunately I already found that service manual and datasheet give specifics for the DIP versions of both of these chips. The chips on my board are QFP with completely different pin arrangements.

author: DC Jack
author_rank: Contributor
timestamp: December 12, 2023, 04:13:19 am
content: Quote from: CaptDon on December 11, 2023, 09:01:03 pmThat's the plan now. I'm in the hunt for a 19" to modify, or a 21" to throw on a universal arcade chassis on the CRT.

author: MrAl
author_rank: Super Contributor
timestamp: December 12, 2023, 01:00:29 pm
content: Quote from: DC Jack on December 10, 2023, 11:52:40 pmHi,Are you sure you want to go through all this just to end up with the resolution of a TV set?Maybe you are working with a higher resolution TV set but can it match the modern monitors of today.To give an example, back in the early 1980's I was doing a similar project although it was not for an arcade game per se', but for use as a general graphics display. I went into the antenna jack and used a modulator type circuit to generate the graphics and work on a channel like channel 3. It worked, but the resolution was poor. As you probably know, the lines up and down the vertical are limited on a CRT TV set, and so I was stuck with very low resolution.Some years later, the Sinclair computer came out and that had the modulator built in. It was a similar situation though, the graphic resolution was severely limited. The number of alphanumerical characters across the horizontal was limited to 40, which is very poor.Now your TV is probably better than that, but how much better even when you tap into the guts. That's something you want to consider before spending time working with it. A modern monitor would most likely be better, if not a lot better.Just something to think about, and you may have other reasons for using that particular monitor.

author: sparkydog
author_rank: Regular Contributor
timestamp: December 12, 2023, 08:29:07 pm
content: Quote from: MrAl on December 12, 2023, 01:00:29 pmI suspect the OP is quite sure.First, you're overlooking the obvious; the board is outputting the resolution of a TV setanyway. Plugging that into an 8k OLED isn't going to magically make the input not-480p. (If it's even that good...) Your example is predicated on being able to take advantage of higher resolution. That Sinclair, for example, plugged into a modern display, is still only going to be 40 characters wide.Second... the "subpixel" layout of a CRT is such that the output on a CRT is significantly different from output on a modern discrete-pixel device. Old games were often designed to exploit this, and there is significant effort trying toreproducethe effect on modern displays. The OP didn't clarify whether "it's not pretty" referred to the conversion job, or the result of having an LCD instead of the intended CRT, but it might well be the latter.

author: DC Jack
author_rank: Contributor
timestamp: December 12, 2023, 09:36:45 pm
content: Quote from: sparkydog on December 12, 2023, 08:29:07 pmExactly this. And the "not pretty" is referring to a few things. The video displayed is not as expected (noticeable latency, and video effects that need a CRT like dithering to simulate transparencies) as well as the physical modification to the cabinet to make it fit. The display uses a 16:9 size television leaving huge unused display area and shows under-scan when the game board is expecting sections of the output to be over-scanned and hidden. Also the output from the game board is not even 480, its even lower at 320!

author: BrokenYugo
author_rank: Super Contributor
timestamp: December 12, 2023, 10:21:37 pm
content: The latency is why I have a small collection of CRT TVs, if you're used to playing fast 8/16 bit games you can really feel it going from a CRT to a LCD. I can stand the look being off, but the feel has to be right.

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 12, 2023, 10:34:28 pm
content: Set the TV input to Game/Computer/Console mode (Name depends on the TV). Most postprocessing will be removed, reducing the delay by a lot.

author: MrAl
author_rank: Super Contributor
timestamp: December 13, 2023, 11:27:00 am
content: Quote from: sparkydog on December 12, 2023, 08:29:07 pmHello there,I did not overlook anything I just didn't realize that anyone would be bothered with something this ancient in these modern times with high res monitors and the likes.I do realize that for some people a call from the past is interesting just the same, and I have an old TRS80 (ha ha) that I think about now and then. It is so ancient it doesn't even have a color display, just a green phosphor CRT.I did an awful lot of work on that thing though including reprogramming part of the operating system, which, are you ready for this ... only allowed file dates up to 1988. That's nuts, but they skimped on the bits used to store the date because back then memory space was at a premium space, with a 40MB (yes, that's 40 Megabytes) hard drive was $400 USD.Just the same, I loved that machine.Just one thing, what did you mean by "subpixel".

author: Andy Chee
author_rank: Super Contributor
timestamp: December 13, 2023, 12:31:15 pm
content: Quote from: MrAl on December 13, 2023, 11:27:00 amI posted one YouTube video a few posts ago from Adrian Black, who is definitely a CRT and 8-bit machine freak.He does a green phosphor tube swap here:And resurrects a TRS-80 Model II here:And a rusty Amiga 500!Yes, much of what Adrian plays with would probably be regarded as e-waste these days! Nevertheless, it's a highly recommended YouTube channel for those interested in technical troubleshooting and repair of necroware, as opposed to merely playing retro games and otherwise using it.

author: sparkydog
author_rank: Regular Contributor
timestamp: December 13, 2023, 06:36:25 pm
content: Quote from: MrAl on December 13, 2023, 11:27:00 amI can totally understand that; it's not something folks that don't pay attention to the retro gaming scene would likely know about. It's worth looking into, though, just because it's a fascinating subject. 🙂Quote from: MrAl on December 13, 2023, 11:27:00 amA full-color pixel on just about any known display device (with the possible exception of color e-ink!) isn't a self contained unit, but consists of separate R, G and B elements, usually as a set of three thin bars that, combined, make an approximate square. (Usually,but not always, these are arrayed so that individual pixels do have the same horizontal and vertical pitch, though I think almost allmoderndisplays do have 1:1 pitch ratio.) Modern software will evenexploit thisto improve resolution, particularly with text. If you've ever seen color fringing on text (orange on one side, teal on the other), that's subpixel antialiasing in action.In addition to having a regular grid of pixels, modern displays are "driven" at exactly their physical resolution. (Mismatches are made up insoftware; the input is scaled to a digital image of correct resolution.)CRTs use a "delta" subpixel layout, where the R, G and B elements form a regular pattern of equilateral triangles. This means that there is not an exact match between the pixels of a digital image consisting of a grid of color values (i.e. what basically everything works with at a software level) and the physical display elements. Additionally, they work withanaloginputs. The result is that the translation of digital image to photons is subject to transformation artifacts that simply don't happen with modern displays... and these "artifacts" can be, and were, [deliberately exploited](https://en.wikipedia.org/wiki/Composite_artifact_colors) to produce effects that were otherwise not possible using the hardware of the time. The result is that the same digital image displayed on a CRT can look very different when displayed on a modern LCD or OLED.See alsohttps://www.cracked.com/article_33451_fact-retro-games-really-did-look-better-back-in-the-day.htmlof search for "crt vs lcd".

author: MrAl
author_rank: Super Contributor
timestamp: December 14, 2023, 11:14:09 am
content: Quote from: Andy Chee on December 13, 2023, 12:31:15 pmHi,Yes that looks interesting. I'm not your typical caveman anymore though, I usually go with the modern stuff, although the older stuff was interesting and you could modify it easier if you wanted to.

author: MrAl
author_rank: Super Contributor
timestamp: December 14, 2023, 11:26:44 am
content: Quote from: sparkydog on December 13, 2023, 06:36:25 pmHello,Oh I see what was meant now with 'subpixel'. When talking about a modern monitor this is usually referred to as 'color components'. Often red is one, blue is the other, and green is the other.I was also assuming a black and white CRT which was the original and what I was using back then.Yeah the different ways monitors arranged their BGR phosphors was interesting. Sony did theirs different at one point and I had one of those monitors. It was expensive too, and yet it had to use very thin wires across the screen to keep the pixel masks from vibrating and causing some blur.Now everything is mostly LCD with LED backlight.The LCD technology really reduced the size (depth) and weight of monitors even though their color gamut was reduced. LED backlights reduced the weight and reduced the size a little more too.At first I hated LCD's because of their reduced color range, but later I welcomed them for TV sets because they were SO much smaller and lighter weight. Sometime after that I welcomed them in for computer use also simply because of the reduced size and weight. I put up with the reduced color abilities even though I never liked that and actually hated it for some things.