Recent content by stepleton

My guess of "partial to full screen" is that the oscilloscope trace of the raw video signal shows scanlines with "stuff" for most of the screen during register display, while it shows mostly empty scanlines during normal display. If I guessed correctly, then maybe I'll have saved patm some...

That said, even with the desoldering gun, you can still run into trouble with through-hole legs sticking to pads with just a bit of leftover solder :) Adding fresh solder and attacking the joint again with the gun can help.

It might be good to know that the BNC connector on the back serves a regular composite video signal. If there's anything there, it will display on an ordinary composite monitor.

I would say yes, in general. You seem committed to the hobby, so you will get a lot of mileage out of a desoldering gun. If you get a quality tool and maintain it (not hard), it will last you for many years. You can build skills with simpler and cheaper tools, and those skills are valuable...

There are several more experienced 5100 owners than me, but I am pretty devoted to the first law of troubleshooting, which is "thou shalt always check voltages" in my scriptures. The 5100 PSU serves five unique voltages to the A1 board: +12V, +8.5V, +5V, -5V, and -12V. Have you got them all...

(wild guess) As it's a three-pin jumperheader, there's a chance that (for example) pin 1 is GND, pin 3 is some "source" signal pin, and pin 2 is IFC. Bridging pins 1-2 pulls IFC to ground, bridging pins 2-3 makes it do whatever the source signal pin is doing, and running with no jumper lets one...

I only knew the first bit (about Eliot Miranda), who we reached out to a while ago; see earlier posts in this thread. Any chance you squirreled away any copies of your own? :) I don't know much about King Crimson, I'm afraid, except for something about mellotrons and a bit of guitar sampled in...

This phenomenon is called "CRT cataracts", I believe. That search term will lead you to a lot of resources.

No worries; it all started when I put the MFM into the computer backwards months ago. I thought I'd fried something, but I hadn't: it turns out to have been the ROM issue all along. If I hadn't suspected hardware, I would have worked out the ROM issue much sooner instead of swapping parts. In...

Update: sure enough, displacing the ROM appears to have helped. I believe I'm ready to move on to the next stage of my project!

Thanks both, I'd noticed that offset too late last night and had wondered if that was what mattered. For what it's worth, the binary file in @nikola-wan 's GitHub repo...

Thanks for the comments! However I think what I just need is to correct my installation of the RS-232 ROM image --- I'm under a bit of time pressure, I have an MFM, and I have a breadboard and a pile of comparators and reed relays to get me where I need to go. As fun as it sounds, I don't think...

Well, colour me surprised: I ran the checksum program, and it looks like whatever I have on the MFM doesn't match what you have: https://photos.app.goo.gl/GsYqBZga4tAL4osg7 When I do CALL "CLIST", I see the same listing you see here...

I've now replaced the 75155s. Everything is as it was before except now Pin 1 (DCD) rests at a little below +3V. The mystery continues. The 4050-series reference manual reports error 67 as: "An attempt has been made to execute an illegal I/O operation on an internal peripheral device. Example...

Thanks for the reply! I didn't think a 4052/4054 MFM could work in a 4051? I haven't tried to use it there and am wary of trying. Can the 4052 MFM work in a 4051? I thought the expansion ports were physically incompatible... I haven't done this, but I will try it if I get desperate. The...