Recent content by A4000Bear

Well, Murphy's law had kicked in. Literally minutes after I posted the original question, I found the link I was looking for. A youtube video by Epictronics I'll include it here in case anyone is interested. Unfortunately, it appears that his variant is also unsuitable, the two additional...

I recently saw where someone had redesigned the layout of the PC-Sprint so that it could fit in his XT clone. From what I remember, the normal PC-Sprint fouled an ISA slot in his computer, so it was redesigned with a long, thin PCB, with the 8284 chips in line. Unfortunately, I had foolishly...

Its possible the colour subcarrier frequency is off, or drifting. If you look closely at coloured areas when the colour is low, do you see 'Hanover Bars'? These are fine horizontal lines of dim and brighter colour. Wikipedia has an article with pictures of what they look like. There is a...

Some questions for you. Has the problem suddenly appeared on a previously working system? Is your system PAL or NTSC? Note: the 1701 monitor does not support RGB or RF.

I have now tried the resistor mod, but unfortunately it makes no difference at all.

Thanks for that. I tried it with the jumper settings recommended there, but no luck. I get the power light going from dim to bright, but after that, nothing. My U38 has a checksum of 90C4, and I have a full 50MHz 030 installed. I haven't yet tried changing R3, 4, 38, & 39 as suggested to 1K...

I found your link to the 50MHz GAL files to be very interesting as I have a 40MHz version of that board, so I decided to try them to upgrade my board to 50MHz. I had previously tried this without success, even though I have a 50MHz 030 installed. It was then that I found that the PALs had to be...

I have just completed documenting my jailbar removal adventures here: https://a4000bear.neocities.org/jail/jail Here are a couple of examples:

Haha! I still haven't figured out why most of my EPROMs don't work as character ROMs!

I found some Motorola 68B45 CRTC chips in my spare parts collection. I had already tried a few different Hitachi 6545 chips with no change in behaviour, so I tried these. None of the 68B45s worked. I got a single horizontal line in all cases. I don't see any reason why the 68B45 won't work in a...

Well, going down that little rabbit hole was a waste of time. I temporarily incorporated the outstanding modification (14) to my board. No apparent difference at all. The machine runs as before. Still good with the original character ROM, but screen shift/corrupted characters with an EPROM...

After a lengthy examination of my board and the schematics, it appears that some of the modifications have already been incorporated, but others have not. Modification 7 was not - but as it applies to the 8032, and my board was originally a 4016, I guess that was no surprise. Modification 14...

It seems those mods listed are instructions for rework after the boards are manufactured. They include things like attaching identification stickers and the piezo speaker, which are things my board has. However my board has none of the cut and jumper mods. In an attempt to determine how common...

I have tried a different CRTC and there was no difference. All my CRTCs are Hitachi ones (including the one that came with the machine). I am aware that different brands of CRTCs can have subtle differences. I may have different ones in some other machines/cards I could try if the brand is an...

I did try 74177s in those spots - luckily I have three of them. I guess a previous owner changed them at some stage. I'm trying to figure out exactly what those mods do, and if I can try them non destructively, without cutting pins or tracks. Fortunately the previous owner had put many of the...