Caluser2000 wrote on 2020-06-15, 22:12:

Disagree completely. EGA runs fine on my XT Turbo running GeoWorks. […]
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derSammler wrote on 2020-05-17, 08:57:

matze79 wrote on 2020-05-17, 08:11:

But VGA/EGA requires NEC V20 or patched Drivers on 3.0

VGA/EGA does not belong into an XT. CGA mono is too slow already, even on a Turbo XT. While it works, it was clearly not meant to be used on XT-class machines.

Disagree completely. EGA runs fine on my XT Turbo running GeoWorks.

If a person is unable to source a mono or herc monitor fitting a EGA card if you have a suitable monitor or an 8-bit VGA card ,or 16 bit vga card that will work in an 8-bit slot, makes perfect sense. Some folk, like me, just do not want to muck around on mono monitors for various reasons. Location, availability, cost of shipping, prefer a colour monitor etc etc...

Better to have a system active with a more modern video card/monitor set up than holding your breath waiting for a specific monitor to show up or wasting hours and hours looking for one. That is one of the great advantages of x86 systems with ISA compared to other systems of the same era.

IMHO, both EGA/VGA are causing less overhead than CGA/Hercules.
It's likely that they both increase performance on XTs, even.
From a pure technical point of view, without considering nostalgia
or socalled period correctnes, there's nothing wrong with VGA on an XT.
In fact, VGA was designed to use the 640KB-1MB range for the framebuffer only,
which allowed for backwardscompatibility with both hard- and software.
(Many first-gen VGA cards included emulation modes for Hercules, CGA and EGA.)
If VGA was made with ATs in mind, it would have used the 15-16MB range, wouldn't it ?

Anyway.. I can also understand that some people prefer Hercules/CGA on XTs. Or Hercules on 286/386, even. 😀
Software before 1987 usually made no use of VGA or little use of EGA only.
And both Hercules and CGA require less memory in the UMA, so the conventional memory can be larger (704KB to 736KB).
It's really the '87 to '91 range in which both EGA and XTs had any relevance (together).
In fact, Hercules likely outlived both of them. After 1992 HGC cards were used
in 286-based terminal computers (diskless stations, cash registers etc) and in
workstations (386+, monochrome card for debuggers etc) still.
At this time, EGA was a relic superseeded by VGA long ago.
Nowadays, EGA, for most people, is mainly remembered as sub mode of VGA.. 😀

Back to topic :-p

I have found a 4.77 MHz board. My Multimeter shows exactly 4.77MHz on the CPU and also on the ISA bus. The Mach-10 is also not running in it. But I noticed there is a clock of 50 Hz applied to the 8086 on the card..so this cannot work.

EDIT: Also noticed my 8086 will not work, I only have the 5 MHz version but I need 10....

I tried to figure out what the way of the CLK is.

So the 4.77 MHz seems to come from the ISA-BUS (not the CPU-connector) and it arrives at the Dallas DS1000 (U31) and the 74S51N (U32). The frequency of the output of the 74S51N seems to be "random", at least my multimeter does not give an exact value...but I think here it should be "converted" to the 9.54 MhZ.

There should also be a jumper to run the 8086 at 4.77 Mhz but I dont know which one. Closing the SW1 doesnt seem to change much.

Then it goes to the 74F04N - and to my surprise there is no output at all, sometimes it shows 50Hz.

Further way is through the transistor I added - which seems to be a quite important part. Also still not sure if its the correct type and if I soldered it the correct way. But no signal arrives at it anyway...

You see I have no idea how this works 😉 Think next I will desolder the 74F04N and check it in my TL866...

Hmmm...can somebody help me with that transistor again please?

So this is the circuit, invisible traces in purple:

And this is my transistor and how I connected it...:

Is this correct..?

Common bean transistors are not made to oscillate at 10mhz, you need different transistor that is rated for these.

Cheers,

derSammler wrote on 2020-05-17, 08:57:

VGA/EGA does not belong into an XT. CGA mono is too slow already, even on a Turbo XT. While it works, it was clearly not meant to be used on XT-class machines.

just your opinion, with VGA i have much faster Video Speed, and the CPU does not need to wait for the Slow CGA/HGC Card.
Its exactly the oposite Situation.

Does the Mach10 only Accelerate Windows ? or is it a complete Upgrade ?

Don't use electrolytic caps in place of tantalums because it could change the characteristics of the circuit. Tantalums can work on higher frequencies and have smaller current leakage than electrolytic.

SW1 also missing on your board?

still do you need help?
Recently obtained worked Mach10. Sadly that documentation/software is missing on the web?

SW1 is for changing CPU frequency from 4.77 to 9.5Mhz , you need to either put jumpers there or a spdt switch. from:
https://books.google.com/books?id=oDwEAAAAMBA … upgrade&f=false

added: I would try a 2n2906/2907 PNP transistor, there were common (the 2n2222 was the npn compliment) and good to over 100Mhz iirc...

Yeah, his 2N2906 should have been fine. General purpose silicon transistors can't do 10Mhz, since when? 1957 when they weren't bipolar type yet? I don't even think most of them in use since 1970 have a problem with 130..140..

BitWrangler wrote on 2021-07-30, 00:04:

Yeah, his 2N2906 should have been fine. General purpose silicon transistors can't do 10Mhz, since when?

I agree that any gen-purpose transistor should be able to drive 10 MHz. But I would like to point out that you have 6 possibilities to distribute the terminal "base", "collector" and "emitter" to the three TO92 pins 1, 2 and 3. And it seems like there are around 3 common "conventions" how to map the pins. If you replace a TO92 transistor with a different model, and especially so if you switch to a different origin (BCxxx transistors are European, 2Nxxxx transistors are American, 2SA..../2SB..../2SC..../2SD.... are Japanese), you better compare the pinouts according to the data sheet. It's not that bad with TO220 power transistors, because mechanical reasons make "center = collector" very likely.

mkarcher wrote on 2021-07-30, 00:16:

I would like to point out that you have 6 possibilities to distribute the terminal "base", "collector" and "emitter" to the three TO92 pins 1, 2 and 3.

Good point ! Good thing the collector and emitter are labeled on the board. Have had to twist some pins around many times to fit a replacement in proper orientation 😀

Yah good point BCE is quite common, worth having one of those $20 eBay component testers around if you've got a lot of randoms you're not sure of. (Plus you can get a basic read of whether caps are still capping etc)

edit: BTW do ya think the Microsoft spokesdroid had his trollface on when he said the 16 bit bus on the 286 crippled performance since it was on 8 bit ISA, yet the 8086 is also 16 bit, 🤣 ... maybe couldn't get 8088s in that speed grade? I dunno... I feel it wants a V30 anyway.

BitWrangler wrote on 2021-07-30, 00:54:

Yah good point BCE is quite common

?

In Europe, the famous BC548 is CBE (BC558 is PNP version).
https://en.wikipedia.org/wiki/BC548

Also, the pinout of the American 2N2222 used to be different.
The historic metal-can type had a different pinout than that 2N2222A in plastic case has now? Or so I heard, not sure. 😅

https://en.wikipedia.org/wiki/2N2222

http://semiconductormuseum.com/Transistors/Mo … ichen_Index.htm

Edit: Flashback! Some XTs, say from soviet union, had 16-Bit extensions (i/0 only) - minus extra DMA controller, extra IRQs etc of course.
So 16-Bit ISA really existed on XT machines, in some way or another. 😀
XT clone with 16-Bit slots ?

Fun fact, also: The 8088 was considered an "castrated" 8086.
Official statement from the original i8086 designer.. 🥳
https://www.pcworld.com/article/146957/article.html?page=2

Making a modern IBM Model 5150 or 5160 replica that's "fixed", not crippled would be cool, I think. 😎👍
Just for fun, to see how it compares.

(With internal 16-Bit i/o, interleaved RAM chips and interleaved eproms, maybe some "full" ISA slots )

That Sergey dude, who made that new XT motherboard, surely has the know how needed, I believe.

BitWrangler wrote on 2021-07-30, 00:54:

edit: BTW do ya think the Microsoft spokesdroid had his trollface on when he said the 16 bit bus on the 286 crippled performance since it was on 8 bit ISA, yet the 8086 is also 16 bit, 🤣 ... maybe couldn't get 8088s in that speed grade? I dunno... I feel it wants a V30 anyway.

As I understand it, the microsoft spokesdroid tried to explain that the win from the 16-bit interface of thr processor is limited due to the 8-bit bus, because everything that misses the local memory cache has to be done in 8 bits. The local cache provides some noticeable gain, though. The 8086 is claimed to collect most of the gain you can get from the 16-bit local cache memory, so there is just a very small unused performance potential left to be picked up by the faster 80286.

mt777 wrote on 2021-07-29, 22:35:

still do you need help?
Recently obtained worked Mach10. Sadly that documentation/software is missing on the web?

Thank your very much for your follow-up! Yes, my card is still not working and fixing it is on my todo list.

Can you please post a photo of your transistor? I would be interested in the exact type and how it is connected.

here are photos
https://drive.google.com/drive/folders/1ZX24C … EwS?usp=sharing

Ah, it's a PNP

Many thanks!!!!!!!!

I have re-uploaded your pictures here - please let me know if its not OK.

To my surprise it is exactly the same one I also tried - see my photo above. But good to know that this is not the reason for the failure of my card...therefore I have to search elsewhere.