| Electronics > Repair |
| Vintage chip Programmer : " Micropross ROM 3000U " |
| << < (9/38) > >> |
| Zoli:
--- Quote from: Vince on November 01, 2022, 09:50:02 pm ---Had a look for local ads.... many hundreds of screens within 20kms around me, incredible... but only 2 or 3 CRT monitors ! :scared: Found this one real close to me https://www.leboncoin.fr/informatique/2020623493.htm A few minutes drive away. 10 Euros (I offered 6 Euros via the website), says it works. A DELL, looks decent and although ad says nothing about model or screen size, it does not look too big which is good as I have zero space, my back is fragile and since we need it for very low resolution pictures, 14" would be plenty enough, so anything above that is already questionable... but you get what you can find, and this one looks overall OK. Sent the guy a message, asking if the thing is still available because... well the ad is a year and 3 months old ! :scared: --- End quote --- VGA monitors start at 31.5kHz&up on horizontal frequency; what you need here is a CGA/Hercules/EGA monitor, since those are capable of 15-16kHz horizontal frequency; or an up-scaler which can handle the signal. Edit: another option would be to generate composite video from the available signals. |
| pcprogrammer:
Like Zoli wrote, I don't think that monitor will do. Here is what Adrian from his Digital Basement is using. https://www.retrotink.com/ It is not cheap but for playing with old computer hardware it saves a lot on space. This is another one he did a video about. https://texelec.com/product/rgbtohdmi-ttl/ Edit: Found something less fancy on Aliexpress https://nl.aliexpress.com/item/4000516564335.html |
| Vince:
Wow, glad I had a quick look at this thread this morning befdore hurrying to work, I was able to send the seller a message to cancel the deal in time ! Mercifully he was very understanding/forgiving, no drama . :phew: I am ust say UI ma surprised that a VGA monitor can't display EGA, I mean lower resolutions in general, since the H/W is capable of it ? I mean you can't ask a 14" monitor to display what a 21" CRT can, because it simply doe snot have the H/W ressources, the bandwidth to do it ! But a 21" can of course display lower resolutions like 1280 or 1204 or 800 or even 640/VGA of course..... similarly I was assuming that any VGA monitor could display preceding video standards like CGA/EGA. I also just found this Wikipedia page about EGA which does say that VGA did support EGA : https://en.wikipedia.org/wiki/Enhanced_Graphics_Adapter Anyway... I don't really have the space for a CRT monitor, and I will gladly buy that 20 buck gizmo from Aliexpress to let me use my existing VGA LCD screens. Not a big fan of composite, because not all my monitors have it, and those that do, I have had mixed fortunes trying to get them to display the composite output from an old VCR I was working on earlier this year. However VGA seems to be present in just about any old LCD screen I get passed, and all of them manage to display the VGA signals I send them, be it from a computer of from my old Tek scopes. OK so I will buy that gizmo, first try to find it on the French version of Aliexpress or other reseller... this will probably take 2 to 3 weeks to arrive, as per usual... so in the meantime I will be able to get back to my other projects / activities. SO, dummy load DIY and PSU fixing.... old man is a bit pushy about me fixing it. |
| Vince:
Forgot. So since VGA is about 30kHz Hsync, for 640 pixels wide, and the programmer is about 15kHz.... I guess that means the video output on the programmer is 320 pixels wide, half VGA ? Is that how it works ? Yes I am not too clued on the technical details.... I noticed that if I divide Hsync frequency by the Vsync one, 15.000 / 46.5 , I get 320 pixels hmmm.... |
| Vince:
OK I just bought that 20+ Euros video converter... from Ebay not Aliexpress. On Ebay I found a seller that's based in France and has stocks locally, so I should receive it much faster than China direct, as well as being guaranteed that I won't have to pay duty taxes if I get unlucky, nor deal with any of the delays and admin BS you can get with importing anything. So I should received it in the next few days normally, great. In the mean time I will resume work on the electronic dummy load to fix that PSU. Oh, last night I had some fun with my nixie counter. Wel, one of my Nixie counters.... my main one that's permanently on the bench ready to go. Was googling to try to find info about timing of H/V sync signal for EGA/CGA, to see i i could find something that matches what I measured. Turns out finding detailled timing info is not that easy... The little I found suggest that my programmer uses nothing that exists ! https://minuszerodegrees.net/mda_cga_ega/mda_cga_ega.htm The Hsync signal is supposed to be 15.7kHz, 63.7µs for CGA and EGA. but I measured 15.4 with the scope, and that's not very accurate. So I measured it much more accurately to be sure of things, using my Nixie counter.... ideal opportuinty to show taht even my vintage counters can still do useful stuff... It measured 15.384Hz and 65.001µs. I read that most monitors are a little bit forgiving about timing accuracy.... so maybe 15.4kHz will still be recognized a valid 15.7kHz signal... I hope. So let's say it's then either CGA or EGA. Now that poses more problem : the width of the pulse on this signal, I measured 8us and this apparently can only be an " MDA "monitor "... but MDA Hsync is not 63.7µs, it's only 54.3µs ! Plus, MDA has a negative going pulse for Vsync, but I have positive going pulse on both H and V... which matches EGA and CGA specs. So... I guess the most probable is, it is CGA but with an MDA pulse width.... But still, there is one thing that worries me... Vsync freq / refresh rate ! The programmer puts out about 46.6Hz , whereas it says taht EGA/CGA is only 60Hz ! So doesn't work... Also, how can 46Hz even exist ? I mean it's such a low frequency that the screen would flicker so badly no human would tolerate that ! :wtf: So all in all my sync signals are inconsistent with old standards, it's a pot pourri. So what I am starting to fear, though I do admit it's a bit paranoid and far fetched (so hopefully I will be proved wrong soon...) is that this programmer was shipped with custom monitor ! One that was tweaked/specced for Micropross to suit their programmer, to make sure customers could not buy a third party monitor on the cheap to save money, maybe. So that custom monitor had maybe a special phosphor as well, with a very high persistence characteristic to get around the very low 46Hz refresh rate. I know, far fetched, but who knows. In any case, not too worried... I am taking it one step at a time. I just ordered that CGA/EGA to VGA converter, so let's wait for that and see what that does for me. We will take it from there... |
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