Recent content by rjarratt

I have to say I don't know or don't remember as it was quite a long time ago.

I have a DECstation 5000/240 which had a PSU problem. I don't know if the 200 uses the same PSU, but take a look at these blog posts of mine to see if they help at all: https://robs-old-computers.com/category/retro-computing/decstation-5000-240/ Regards Rob

Hello again. I haven't been able to look at the VT100 again until today. I decided to try a regular PC PSU supplying the VT100 video board, just to exclude any possibility that the VT100 PSU might be causing any issues with the over/undershoots. I know I was told the PSU would not be the problem...

I think Henk is right, the box is just terrible. It would be good to take a closer look and see what is salvageable. Cirencester is quite a way from me though, not sure I would make the journey specially given the condition of the machine.

Yes I calibrated the probe by connecting it to the two contacts on the scope designed for this purpose. I used a plastic tool to turn the dial until the square wave was perfectly square. Only then did I try to measure the signal on the chip. I tried to keep the length of the ground as short as I...

I checked my probe against the scope's calibration output and used a test clip so that I could connect the probe ground wire directly to the chip's ground pin. This is what I got: So I think the under/overshoot is genuine. How do I go about finding the cause?

That might be a good idea, but I would prefer to get to the cause of the excessive heat really (if I can!)

Thanks Alon. I am using a 1:10 probe. I am pretty confident that the probe I was using was calibrated using the scope output, and I was using the same probe on the good VT102 as the bad VT100. However, I do know that I would not have connected the probe ground wire to the chip's ground pin. So...

I just measured 5.1V on Vcc to the chip. This chip is a recent replacement for the original one because I thought it might be faulty, so it shouldn't be a bad part if both of them get hot. A few posts back there was discussion about the under/overshoot because there is some of that going on...

There is certainly the space to add a heatsink, but I think there must be an underlying problem causing it to get so hot in the first place. As noted in my last reply, the same chip in a VT102 does not get anything like as hot. Maybe I could add a heatsink anyway, just to try to help it out.

I did wonder if it might be normal, but I checked on a working VT102 and the same chip does not get anything like as hot. I can smell the heat and it is too hot to touch. I have been trying to use my multimeter to measure the temperature as it has a temperature function. I don't know if I am...

Well @bigfix sent me two DC012s. I took the old one out, soldered in a socket and installed one of the "new" chips. As you can see below, the external video now works! :) I now need to reassemble the monitor board and see if the flyback is OK, but I have a strong suspicion that it has failed...

I have been trying to find these parts in the UK but I have not been able to find them. Maybe other similar fasteners would work. Maybe once I get the VT100 working again I will try to find them.

I have been looking at this further and comparing my faulty VT100 with a working VT102. I suspect that the DC012 chip may be faulty in that the scan count outputs (SC0-SC3) seem to be only ever all zeroes or all ones. On the working VT102 I can see these outputs count up from 0-8 then F then...

I hadn't considered that it would be the first row of pixels, only the first row of characters. When I use characters that have pixels at the top then I do see them repeated all the way down the screen. What is curious though is that it isn't just characters like the vertical bar, which has a...