VGA card mystery

[KenEG]

For some time now my Commodore Colt with a Video Seven VGA-16D card in it has had an intermittent problem. Sometimes when turned on there would be no video. Usually turning it off and back on would cause it to work. Friday it wouldn't come on so I tried cleaning the card edge of the card, switching cables and monitors, and finally playing with the display switches on the back of the computer. That seemed to fix it. Tried it Saturday and couldn't get it to work at all. I have a DTK XT-Turbo with a old OAK Technologies 8 bit card in it. The Video Seven is an 8/16 bit card. So I pulled the card out of the DTK and installed it in the Colt. Works great! So I put the video seven card in the DTK figuring it wouldn't work. It works perfectly. I have periodically booted both computers and they have continued to work.

Anybody her have an idea as to what is going on? I am happy right now, but fear an impending failure.

 

[Hugo Holden]

and finally playing with the display switches on the back of the computer.

I assume you mean the dip switches on the Video-7 card ?

The probability of an intermittent electronic fault is mostly lower than an electro-mechanical one. So if one takes the reasoning that it is an intermittent connection "somewhere", where would that likely be?

Actually, it is pretty unlikely on the board's edge connector, because when you plug those in and out the mechanical friction cleans the gold surfaces, but it is still worth cleaning. If there are any IC's in sockets on that Video-7 board, remove the IC's and clean the pins & socket and re-fit it observing anti-static precautions.

One area I have seen is DIP switches giving trouble. The mechanism inside them does not self clean the contacts well when the switches are exercised, so they go randomly open circuit, especially when they are old and the Gold plating inside them acquires a non conductive layer. Spraying cleaner into them is useless. So, if all else fails and it is still behaving in an intermittent manner, replace those switches, if on that card, with new manufacture ones. I don't know your card, it might have jumpers too.

Having said the above I recently had an "Intermittent IC" in my SOL-20 computer, a flip flop where its output vanished, fell to zero volts, just from time to time, disabling the keyboard. But those are the things nightmares are made of and they are pretty rare compared to more common problems. Also it was not temperature sensitive either.

 

[KenEG]

Thanks for the reply. No I meant the switches on the back of the computer. It has a built in CGA/monochrome adapter that has to be either disabled or set to monochrome to work with an ISA video card. I didn’t try messing with the switches on the card. There are socketed chips on the card, so if I have any more trouble I will try resetting them. As I have been thinking more about this, I am wondering if it is a power issue. The DTK has a bigger supply and has an XT-IDE adapter with a DOM in it. The Colt has a smaller supply and an actual hard drive. Maybe the DTK has enough power to get through an iffy connection, but the Colt doesn’t? If so it will fail again when the corrosion gets worst. My other theory would be capacitors on the way out.

 

[Ruud]

IMHO the Colt is the same as the PC10/20-III. At the moment I'm using a Tcheng(?)-4000 VGA card. My problem: the PC sometimes starts up in monochrome mode. Why? I have no idea at all. The state of the dip switches at the back don't matter. In the past I had the same problem with other VGA cards as well so but it is so rare, once in every 25 power-ons I guess, that I just leave it that way.

 

[Xacalite]

My problem: the PC sometimes starts up in monochrome mode.

Most likely it's because the card pays attention to the Monitor ID pins, especially pin 12 - not connected in the original IBM VGA color monitor, connected to GND in monochrome monitor.
Later monitors use pin 12 for DDC, so it's sometimes 0, sometimes 1.
It's easily remedied in software, eg. Trident cards come with SMONITOR utility to set the monitor type.

 

[Ruud]

This is new to me. And to make it more exiting: I use a KVM switch.

 

[Miggy]

This is indeed a known problem: I have it on my PC20-III with a Trident 9000 VGA in combination with a Sony crt-monitor. Other combinations of VGA-cards and monitors in the same computer don't have it, but I really wanted to use that combination of hardware. It really annoyed the hell out of me and at first I thought it was caused by defective hardware or an incompatiblity. Neither is true, although the latter comes close.

Solved it with a small utility I found in a thread on Vogons, concerning this problem. I would prefer to solve it hardware wise on the videocard, as I understood it is rather simple for someone with the needed skills , but I don't trust myself cutting/drilling/soldering or otherwise severely risking my hardware...

The utiliy I use (coloron.zip) can be found in this thread on Vogons.