HanJammer wrote:

N00b question - is it even possible to hookup MDA/hercules monitor to CGA and/or EGA card? There is an explanation (well sort of […]
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N00b question - is it even possible to hookup MDA/hercules monitor to CGA and/or EGA card?
There is an explanation (well sort of) at: https://stason.org/TULARC/pc/video-faq/45-Wha … A-EGA-card.html
and it seems with EGA it's possible, while with CGA not so much (although I remember using hercules in CGA modes back in the early 90s) with regular hercules monitor...

I need it only for testing purposes, but I would rather not damage the monitor trying to force modes on them it can't handle... Also I can test CGA cards using the coaxial output so in fact I only need it for EGAs mostly...

Yes for many EGA cards. The jumpers will control it's output type. You will not get CGA or EGA modes outside of high res monochrome EGA.
A fantastic card I've found for testing purposes is an ATi EGA Wonder - It will attempt to autoswitch to what monitor type you have, and attempt to scale other modes to fit on that screen. EGA hi res color on a composite television and such. It's almost invaluable.

CGA modes *might* display on an MDA monitor, depending on whether or not it will drive the monochrome pins or not. Otherwise, it's a no.
You can emulate CGA modes with a Hercules card using some TSRs, if that's what you mean, though.

If you know what kind of EGA card you have, you can set the switches to "MDA" or "TTL," whichever it lists in the manual. Otherwise, flip switches until it boots... I've done this before to make a card work.

FAMICOMASTER wrote:

Yes for many EGA cards.

Yes for ALL EGA cards.
And yes, the DIP-switches must be set for monochrome monitor.
And yes, with regular EGA cards, when set for monochrome, the only available modes are 7 and F.
But there are some special EGA clones, notably the ATI EGA Wonder series, that can display any mode on any monitor.

CGA cards can't work with MDA/Hercules (18 kHz HSYNC, 50 Hz VSYNC) monitors.
And the original IBM 5151 monitor is known to be damaged when fed with CGA signal.
Later clones are probably safe, and many of them are actually "dual" monitors, designed for both 18 and 15 kHz HSYNC, so yes, they have a chance to work with CGA cards.

Grzyb wrote:

Yes for ALL EGA cards. And yes, the DIP-switches must be set for monochrome monitor. And yes, with regular EGA cards, when set f […]
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FAMICOMASTER wrote:

Yes for many EGA cards.

Yes for ALL EGA cards.
And yes, the DIP-switches must be set for monochrome monitor.
And yes, with regular EGA cards, when set for monochrome, the only available modes are 7 and F.
But there are some special EGA clones, notably the ATI EGA Wonder series, that can display any mode on any monitor.

I did not want to say "All" because I'm sure there's some special OEM card out there that can only drive EGA and MultiSync monitors.

Pretty sure I mentioned all of this as well, including the EGA Wonder part. It won't always display properly on all monitors, however. In some cases it will have parts of the image cut off or the monitor can lose sync.

CGA cards can't work with MDA/Hercules (18 kHz HSYNC, 50 Hz VSYNC) monitors.
And the original IBM 5151 monitor is known to be damaged when fed with CGA signal.
Later clones are probably safe, and many of them are actually "dual" monitors, designed for both 18 and 15 kHz HSYNC, so yes, they have a chance to work with CGA cards.

The 5151 is known to be damaged when fed a CGA signal? In what manner? Every MDA monitor I've tried will just lose sync with it - The picture rolls vertically or it will blank out.
I'd love to hear more about this, are IBM's monitors really that terrible?

FAMICOMASTER wrote:

I did not want to say "All" because I'm sure there's some special OEM card out there that can only drive EGA and MultiSync monitors.

Well, it's possible, with so many clones, some of them may actually be crippled.
Nevertheless, the original IBM EGA and all proper clones are designed to work with three kinds of monitors: 15 (CGA), 18 (MDA/Hercules), 15/21 (EGA) kHz HSYNC.

The 5151 is known to be damaged when fed a CGA signal? In what manner? Every MDA monitor I've tried will just lose sync with it - The picture rolls vertically or it will blank out.
I'd love to hear more about this, are IBM's monitors really that terrible?

AFAIR the flyback transformer gets damaged.
And, to quote from http://www.vcfed.org/forum/showthread.php?222 … 4849#post154849 :
"the 5151 has no horizontal oscillator--it just takes whatever is sent over the horizontal sync line and uses it"

Grzyb wrote:

AFAIR the flyback transformer gets damaged.
And, to quote from http://www.vcfed.org/forum/showthread.php?222 … 4849#post154849 :
"the 5151 has no horizontal oscillator--it just takes whatever is sent over the horizontal sync line and uses it"

Hmm, I suppose I could see a flyback melting if it's fed an improper signal, but wouldn't the flyback's driving electronics fail long before the flyback itself overheats? It's quite a large component, and a relatively tiny transistor will almost certainly pop before it can dump current into a high voltage coil.

Yeah, that's how an awful lot of CRTs work - Most analog ones, in fact. If it doesn't have an OSD, it's just taking whatever signals are coming from the device it's attached to and drives the CRT like that. This is why (most) analog monitors can display an incredible variety of resolutions.

FAMICOMASTER wrote:

The 5151 is known to be damaged when fed a CGA signal? In what manner? Every MDA monitor I've tried will just lose sync with it - The picture rolls vertically or it will blank out. I'd love to hear more about this, are IBM's monitors really that terrible?

It is, that and many more. It's not a terrible monitor though one that doesn't work way out of specs.
The same will happen to monitors appearing to be working or loosing sync, if you keep them running like this long enough.

FAMICOMASTER wrote:

Yeah, that's how an awful lot of CRTs work - Most analog ones, in fact. If it doesn't have an OSD, it's just taking whatever signals are coming from the device it's attached to and drives the CRT like that. This is why (most) analog monitors can display an incredible variety of resolutions.

TVs, by their nature, generally do not work that way.
They have their own oscillation circuit, which is synchronized to the input signal, within reasonable parameters.
Otherwise any TV would blow up as soon as you turn it on without it being tuned to a proper channel (or just forgetting to plug the antenna in).
So if a TV doesn't get a proper sync signal, it will just be 'slightly' out of sync, and still within reasonable parameters, so nothing gets damaged.

Since many early colour monitors are based on TV technology, they also have this circuitry in place. Some MDA monitors also have it (I know my Philips one does, but then again, Philips was one of the largest CRT/TV manufacturers back in the day), but generally MDA monitors were just made to be as cheap as possible, like the 5151.

So rule of thumb is that colour monitors are safe, but MDA monitors are not.

Yep. "Sync" on the 5150 is actually a misnomer, since the HV pulses actually drive the deflection directly

konc wrote:

It is, that and many more. It's not a terrible monitor though one that doesn't work way out of specs.
The same will happen to monitors appearing to be working or loosing sync, if you keep them running like this long enough.

I have my doubts, but I don't seem to have any such monitors, and I'm not about to spend a few hundred to get one if they're actually as bad as this - I'll just take your word for it.

maxtherabbit wrote:

Yep. "Sync" on the 5150 is actually a misnomer, since the HV pulses actually drive the deflection directly

The 5150 does not generate anything near high enough voltage to drive deflection electronics directly - It doesn't position the beam either. I'm 100% certain that it does not - It's bitmap, not vector.

Scali wrote:

TVs, by their nature, generally do not work that way. They have their own oscillation circuit, which is synchronized to the inpu […]
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TVs, by their nature, generally do not work that way.
They have their own oscillation circuit, which is synchronized to the input signal, within reasonable parameters.
Otherwise any TV would blow up as soon as you turn it on without it being tuned to a proper channel (or just forgetting to plug the antenna in).
So if a TV doesn't get a proper sync signal, it will just be 'slightly' out of sync, and still within reasonable parameters, so nothing gets damaged.

Since many early colour monitors are based on TV technology, they also have this circuitry in place. Some MDA monitors also have it (I know my Philips one does, but then again, Philips was one of the largest CRT/TV manufacturers back in the day), but generally MDA monitors were just made to be as cheap as possible, like the 5151.

So rule of thumb is that colour monitors are safe, but MDA monitors are not.

Well first of all, I didn't say anything about television. This is about computer monitors.
A television with an improper input will just end up with a rolling picture or losing color, all number of other minor symptoms. It won't be damaged by it because there's nothing to damage.

Kinda sucks they would be that cheap - I can't imagine it would save much, if any money to exclude what in most televisions and monitors is driven by a subsection of a single chip at that point. They already have to have translation electronics to actually receive the TTL signals, it can't have cost but a fraction of a few pennies to just attach the connection.

If an MDA monitor truly is direct drive, then I still have difficulty seeing how one might be damaged by improper synchronization, since many CRT oscilloscopes have no problem receiving any signal in X-Y mode, which disables the oscillator inputs entirely. If the 5151 and other monochrome monitors truly have no oscillator, they should be able to sync to just about any signal you feed them. If they're being directly driven by the video electronics, there is no reason it can't just... Feed it different signals.

I.E. Unless the monitor is generating SOME signal of it's own, it can take any signal as timings for the scanning speed.

There have to be sweep electronics internally, since the MDA/Hercules boards do not generate that on their own. The monitor is almost certainly always sweeping at a fixed speed a fixed amount of time after the horizontal pulse, and there is likely at least a basic counter or sweep electronics to drive it vertically.

Many of the signals needed to produce a valid picture are not included on an MDA card, so there has to be some oscillator inside the monitor, otherwise it's a glorified oscilloscope stuck in X-Y mode.

FAMICOMASTER wrote:

maxtherabbit wrote:

Yep. "Sync" on the 5150 is actually a misnomer, since the HV pulses actually drive the deflection directly

The 5150 does not generate anything near high enough voltage to drive deflection electronics directly - It doesn't position the beam either. I'm 100% certain that it does not - It's bitmap, not vector.

yeah sorry if that was unclear, I actually meant to type 5151 - as in there is no PLL in the monitor - I was not trying to run some BS about there being high voltage in the video cable

FAMICOMASTER wrote:

Well first of all, I didn't say anything about television. This is about computer monitors.

Yea, that's the second paragraph, the TV part was just an explanation.

Over on VCF, we actually discussed the schematics of my Philips MDA monitor, which contains the extra circuitry that TVs and most colour monitors also contain, but the 5151 does not.

FAMICOMASTER wrote:

The 5151 is known to be damaged when fed a CGA signal? In what manner?

It's an urban legend spread on forums without actual proof. Nobody dares to try it so they just ASSUME it's going to blow up or something. Fear of losing a valuable monitor is enough for people to stop them from experimenting. Understandable, but anything else is just mere speculation.

Miphee wrote:

FAMICOMASTER wrote:

The 5151 is known to be damaged when fed a CGA signal? In what manner?

It's an urban legend spread on forums without actual proof. Nobody dares to try it so they just ASSUME it's going to blow up or something. Fear of losing a valuable monitor is enough for people to stop them from experimenting. Understandable, but anything else is just mere speculation.

CGA signal perhaps, but I have heard from various people that reprogramming the 6845 CRTC on an MDA/Hercules card improperly can indeed fry a 5151.

Scali wrote:

CGA signal perhaps, but I have heard from various people that reprogramming the 6845 CRTC on an MDA/Hercules card improperly can indeed fry a 5151.

I've read the same thing when I was experimenting with my clone monochrome monitors and CGA cards. If I had the 5151 I'd test it out myself and post the results here. Those people you mention didn't post evidence of those claims I presume? Fried circuits? Test cards? Testing environment?
So I can just claim that the 5151 doesn't go bad at all with a CGA signal and people should just accept it because I said so.
But I agree that it's better safe than sorry even though I don't accept anything without actual photo proof and test details.
I have an amber monochrome clone coming in soon that is 100% not CGA compatible and I will test all my CGA cards with it. I'll post all the results here when I'm done even if the monitor does fry.
In the meantime someone should be brave enough to try his 5151 with a CGA signal and make a photo of the screen output so we can finally prove or put this myth to sleep.

Miphee wrote:

I've read the same thing when I was experimenting with my clone monochrome monitors and CGA cards. If I had the 5151 I'd test it out myself and post the results here. Those people you mention didn't post evidence of those claims I presume? Fried circuits? Test cards? Testing environment?

Well no, but that was possibly because it happened 30 years ago.
These people are not just 'random' people, but include people like Trixter and ChuckG (author of the well-known SIMCGA software, who claimed to have some mishaps during development of that tool).

Miphee wrote:

So I can just claim that the 5151 doesn't go bad at all with a CGA signal and people should just accept it because I said so.
But I agree that it's better safe than sorry even though I don't accept anything without actual photo proof and test details.

Well, here's another argument:
I see no point in even trying. What would you want to achieve anyway? MDA monitors use entirely different timings to CGA, so even if they don't fry, they will never produce an actual image from CGA, not even if you rewire the RGBI signals to the MDA pins.

EGA is different, since EGA has a 350-line hi-res mode which can be used for both text and graphics, and that mode is compatible with MDA timings, which was a conscious design choice of IBM.
The 200-line modes are compatible with CGA timings, again a conscious design choice, so they will not work with MDA monitors.

Scali wrote:

I see no point in even trying. What would you want to achieve anyway?

I guess I just want to see for myself. What you wrote is true though, I won't gain much but satisfy my curiosity. Everything is done to death with these old computers and everything is thoroughly documented. What I miss here are the tests that aren't supposed to happen: incompatible hardware put together to see what they do. Will they blow up? Will they work? What am I supposed to be seeing when I put a mono monitor on a CGA card? This very question was asked because HanJammer wanted an answer other than a solid NO. These tests might help others when dealing with unknown hardware without proper manuals. Just last month I was dealing with a generic mono monitor with all labels peeled off. Okay, it's hercules compatible, but is it CGA compatible? Won't know without trying. I try it so others don't have to risk it.

Miphee wrote:

These tests might help others when dealing with unknown hardware without proper manuals. Just last month I was dealing with a generic mono monitor with all labels peeled off. Okay, it's hercules compatible, but is it CGA compatible? Won't know without trying. I try it so others don't have to risk it.

Yea, but what are you going to do?
Each test you do is only valid for that particular combination of hardware. There are so many possible combinations out there, that it seems futile.

Miphee wrote:

I guess I just want to see for myself. What you wrote is true though, I won't gain much but satisfy my curiosity. Everything is done to death with these old computers and everything is thoroughly documented. What I miss here are the tests that aren't supposed to happen: incompatible hardware put together to see what they do. Will they blow up? Will they work? What am I supposed to be seeing when I put a mono monitor on a CGA card? This very question was asked because HanJammer wanted an answer other than a solid NO. These tests might help others when dealing with unknown hardware without proper manuals. Just last month I was dealing with a generic mono monitor with all labels peeled off. Okay, it's hercules compatible, but is it CGA compatible? Won't know without trying. I try it so others don't have to risk it.

Just because you haven't done something and you don't trust others, doesn't automatically make it a mystery waiting to be solved. Others have. I get it that you want to see for yourself though.

Scali wrote:

Each test you do is only valid for that particular combination of hardware. There are so many possible combinations out there, that it seems futile.

You could say the same thing about everything here so by that logic building computers and sharing information would be equally useless.