jdgabbard

Yeah, I'm deathly afraid of High Voltage. So no risk of me poking around with that thing until it's unplugged and discharged. I do not like anything over 36v DC, lol Here is my blog post on the acquisition: http://retrodepot.net/?p=158

Well, I bought a couple of Kaypro Computers (A Kaypro II and a Kaypro 2X) today for $60 and a few hours drive time. The Kaypro 2X seems to boot ok (I do not have a boot disk to verify), as it asks you to place a disk in the A drive. However the Kaypro II appears to be modded. I'm assuming it was some type of ROM banking (there is a toggle switch that goes to the back on the computer). Does anyone have any idea what is going on here? I can probably dump the rom, but I'd hate to desolder it without having a replacement (I do not have any 2732 eproms). See the attached photo. The computer is dead at the moment. At first when I tried to boot it I heard a high frequency chirping coming from the power supply, and there was no power on the rails. However, I disconnected the power cables from the floppy drives and it appears to stop chirping and there is now power on the rails. However, the CRT does not power up. So this is likely going to take a little work to get going. I gotta be honest, I know nothing about CRTs. All things considered, if the one still works I'm still happy with the purchase. But I'd like to get both working.

Well, I've never used a PDP-1, but I can tell you that on the simplest of "Panel Operated" Computers, they typically do not have an auto-advance. But even if you do, mistakes still happen. And one byte entered incorrectly could mean you have to go through the entire code in memory to double check. Now, on mine I added the ability to increment and decrement the address location being viewed (It was a software driven panel, I'm not sure what he PDP-1 has). This allowed me to start at the bottom of the address space in question and scroll through the code fairly quickly checking for errors. However, it's still VERY time consuming when you're talking about KBs of code. That is another reason I wanted Intel Hex transfers on my new project. I can literally transfer 32k of code and verify it in just under 30 seconds.

Honestly, 98 was king. There is a reason people continued to use it into the 2010s. Of course, the longest reign would go to XP I suppose. But in the end, 98 had everything one needed. It was the first of the "Modern" OSes. Everything we have now is essentially a reincarnation of that early version.

Not really purchased this week, but arrived this week. I got my order of CoCo Cartridge PCBs that I ordered from Elecrow.

Here is a short article about it over on my blog: http://retrodepot.net/?p=117

James, I do not know if you have or not confirmed memory locations on a computer with switches. All I am saying is that yeah, it doesn't take too long to go through a small program. But a large one can force one to sit there examining locations for quite some time. Especially if he missed a byte, or doesn't know which one he entered correctly. I know on the first z80 computer I made I decide to create a breakout Hex keypad so that I could plug information into the machine faster, and scroll through memory locations faster. Because without it, my larger programs were simply taking forever. As far as the PDP-1 is concerned, I'd have to think you'd be correct in that they probably had a paper tape boot strapper embedded in memory. Once the fascination with flipping switches wears off, and you just want to test some real code, you start looking for faster ways of getting it into the computer.

Ok, if anyone wants an Open Source CoCo Cartridge Shell, here are my GNU GPL STLs over on Thingiverse. https://www.thingiverse.com/thing:2536842

You make the assumption that you know which byte wasn't entered correctly. In either case, checking 1000s of bytes of code can be tedious. Trust me, I've had to do it a few times...

I watched this video the other day. Great video.

Just added another update to the project.

Thanks Mark. Btw, I think we are both members of some of the same groups on FB...

Interesting. A PC-88 has always been on my list of 'I'd like to own one, but I have to pay bills' list.

Not in the current configuration. On the final board there will be 64kB of Ram that is banked by way of 74LS74. So CP/M should be able to run on it with a suitable bios. However, this computer is not that much different from the way CP/M operates. The idea is to have system calls, that reside in low memory, which the user can make calls to in order for their program to function. Such as conin/conout. This make porting CP/M compatible software easier, as you simply have to change the system calls in the source, and the . ORG to compensate for running at 8000h rather than 0100h.

I have been working on this computer for a while, and just recently got the monitor to the point that I'm ready to begin showing it to the masses. The computer itself is still a work in progress, the finalized board will have a graphics chip, mass storage, and a fair amount of I/O. But, for now it is simply communicating over serial. Software wise, I am planning on porting Tinybasic, as well as writing some disk utilities. Even though it's not finished, I figured I would share it.

Good afternoon. I'm curious if anyone has any STLs for CoCo cartridge shells? I've seen there are at least some schematics and board files for PCBs on the Web. However, I'm not seeing anything for the shells. I'm guessing I'll probably have to design them myself and upload to Thingiverse. But before I go through the print/test odyssey I figured I would ask. Surely there has been at least one person think about this before now... P.S. I have seen the one for the SDC, and while it should work, it isn't a general purpose shell.

I watched this episode when you released it the other day (yeah, I'm subscribed...). Good video, it actually got me thinking about all of those older software companies that went belly up in the 90s. I was just a kid back then, but what a great time in computing history!

I'm looking for the HDD Cover for a 486 laptop of mine. I do not know why I would think someone would have just the cover laying around and not be using it with their computer. But hey, I've got a computer with no cover, so it's worth a shot. They obviously get separated.... There is a picture of the cover linked below. Hopefully someone can help me find one. If not, I guess I could always 3d print something close. But it would be nice to have the original.

I'm looking to get pointed in a general direction for learning about the MC6845/6545 families of CRTCs. Are there any Gurus on here, or can someone point me to a in-depth site where I could get some good information? My ultimate goal is to design a Video Board for my homebrewed z80 Computer that can be accessed through an 8255 PIO. I've managed to find some information, a one or two schematics, but they all seem somewhat cryptic, insofar as they assume that you already know where some of their signals go (they do not terminate on the schematics, or have no explaination of the control interface with the uProcessor). About the closest I've seen to what I'm wanting to do is the N8VEM VDU board that is at the page located here: http://obsolescence.wixsite.com/obsolescence/the-vdu-board However, there are no schematics for it on the Wiki, as they have moved on to the CVDU board that utilizes the Commodore 8563 chip. Although it seems as though they still sell the boards. Worse, I'm not sure who even designed the VDU as unlike many of the other boards for the project it doesn't have the name of the designer on it in the pictures I have seen. I've already sourced the datasheet for the MC6845 and have read through it, and have a basic understanding of how it works, but it never hurts to see someone else's work so that you can get ideas of how others have solved problems. One of my biggest issues is understanding how integrate Video Memory in the form of SRAM rather than the smaller DRAMs. Here is where I'm sure that there is at least one example of a similar hack, again with the N8VEM group and their use of the TMS9918 with SRAM, but the information was stored on the old PBworks page and seems to have been lost. Does anyone have any resources they could share?

I've done the video mod along with the new keyboard from the source above. Both work great. I have one that I actually modded to use a tactile keyboard that I build and installed into the case. It works as it should. Hope you get it working.

Hrm.... I wonder if he would do a IMB PC/XT replacement supply... This is interesting, I'm going to have to bookmark his site.

I was changing out the battery on a Genesis/MD cartridge when I discovered something that has me baffled. I cannot readily explain it, so I figured I'd post the information here and see if anyone else may be able to shed some light on the reasoning for the design. So the cartridge in question is a EA Madden 95 board, version P10002 Rev M. On the SRAM's VCC line (ie, From the battery backup circuit) there is a decoupling capacitor in parallel with a 2meg resistor to ground. The particular SRAM is the Goldstar GM76C88ALK, and the capacitor seems to be a radial 100nF. Now per my reading of the datasheet, the Goldstar SRAM has a standby current of about 2uA. Obviously there would be some small bleed from the capacitor. However, the Resistor would also have a current bleed to ground of around 2uA. Obviously the current leakage through the capacitor would be nothing of major concern, I question the reasoning of the resistor. Is there something I'm not catching here, or is it as if EA wanted the batteries on these boards to eventually die? Maybe this was in an attempt to be able to sell the upcoming games, since the old game may prematurely loose power from the battery? The only logic I can see with this particular resistor is for the purpose of slowly bleeding the battery. Or is there something about the 1026B battery backup circuit that is clunky without this particular resistor? I opened up a traditional Genesis cart, ESPN Speed World - PCB is 171-6278A, and notice that there is absolutely no resistor to ground. Considering that it is using the same GM76C88ALK and has a very similar battery backup circuit (BA6162), I see no real purpose for the 2meg resistor other than those of malicious intent. Any thoughts?

Yeah, as mentioned above I would try cleaning the port and checking the pins to make sure they're not bent out of shape. I had a similar problem with my SNES last week. On that one it turns out it was the solder joints on the cartridge itself that had broken contact over time. Reflowing with a little 60/40 was all it needed in order to make it come back to life.

I do not have the means at the moment for doing any label work. My only printer is a B&W Laser, although I do have a laminator that would come in handy.... Anyhow, I'm looking for someone, or a web service, that can do custom labels without charging an arm and leg.

It was a few bad solder joints. From the looks of it, it has been reworked at least once. I cleaned it up with some 90% isopropyl, applied some fresh flux, reflowed with a little added 60/40, cleaned and tested. Works 100%. Thanks guys, now I'll be set to play some Gradius later.