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Numitron
April 6th, 2016, 11:05 PM
Hello everyone here on the VCF. I'm new here, though I've been lurking for a while. As you can guess from my name, I've always loved restoring old tech (learned my first electronics on an old tektronix tube (valve) oscilloscope) and making stuff work again in general. I'm currently in college in physics, so you can guess that I would be a bit young to be in this hobby as my nostalgia can only go back to cassettes and 3.5'' diskettes.
Still, despite most of my entourage not understanding why I get all excited over an obsolete piece of tech, I started collecting old computers when I could get them, first a Radio Shack CoCo from a family member, then a TRS-80 model 100 from a customer in exchange for repairing their computer, both of them non-functional until I repaired them. (Anecdote: I nearly started a fire repairing the CoCo because of a reaction of the foam with cyanoacrylate glue)

I got more serious about it recently. I won an auction on ebay for a 5150 restored unit + 5151 monitor for 90$US. It's still stuck back in the forwarder warehouse until I can afford (translate: enough disposable money) to haul it back here in Montreal, Canada, which is around 130US (or 10 billion Canadian pesos, thanks exchange rate) for the whole thing along with a cassette deck for the CoCo, a Model F keyboard and a bunch of floppies. This has nothing to do with the subject at hand but just wanted your opinion on the thing.

REAL SUBJECT STARTS HERE

Alright, so I got this other 5150 in ''meh'' condition I found locally for 60CAD, guy said it was working. It is a 5150 unit upgraded with an XT power supply, full height 10MB miniscribe hard disk, 2 half-height 5''1/4 floppy drives with appropriate controllers, an AST SixPak+ and what seems to be a Hercules clone card (same layout as the original board, but with no branding or code and a seemingly modern PCB mask). It was of course, not working. Dissassembled the thing, immediately went to the PSU, which wouldn't start in no condition. I checked the mobo for damage and found the shorted C7 tantalum in seconds (I was really lucky, hit the defect on first try, was closest C7 to PSU). I think I have 10uF tants on hand to replace it.

As for the PSU, I spent a week trying to troubleshoot the thing before giving up (why wouldn't it start?!), nearly desoldered the whole board and testing every darn component and found niet. I went to the computer club (I run the physics club at my college. We repair computers for them, go figure) and found a modern AT PSU basically just lying on the floor with other crap. I ''borrowed'' it, gutted it and transplanted it inside my XT PSU (https://goo.gl/photos/eYaF34Dyq872Ke8t8) (as some people suggested here) with a lot of hot glue, wood and positive thinking. Works like a charm. Hard drive spin up and nothing explodes for now.

Now... If you read my introduction, you know that my mono monitor and XT keyboard is still on the opposite side of the continent. So, I can get a keyboard using an Arduino programmed as a PS/2 to XT converter, but how can I get a way to get a monitor output? The hercules only output TTL video signals. I wondered if there was any way to convert that signal to something readable using common displays without modifying the display card. I found a few things online that may help, including this (http://www.reenigne.org/blog/i-bought-an-xt/) but I would need a digi-key order to get the parts, and the guys didn't even test it.

I also thought of using an analog TV repair oscilloscope to act as a monitor, by inputing the V/H sync to XY, and video signal to Z/trig. Though I don't know enough about that TTL video signal to even know if that's even doable. I have done TV-scope circuits back in high school but that's it.

What are your thoughts?

Thanks to all.

modem7
April 7th, 2016, 12:39 AM
Welcome to these forums.


I also thought of using an analog TV repair oscilloscope to act as a monitor, by inputing the V/H sync to XY, and video signal to Z/trig. Though I don't know enough about that TTL video signal to even know if that's even doable.
No. The problem is that the sync out of the card is a pulse (see scope pictures at [here (http://www.minuszerodegrees.net/mda_cga_ega/mda_cga_ega.htm)]) that occurs at the start of the sweep. What the oscilloscope would require for XY is a ramping voltage (over the duration of the sweep).

modem7
April 7th, 2016, 12:54 AM
Now... If you read my introduction, you know that my mono monitor and XT keyboard is still on the opposite side of the continent. So, I can get a keyboard using an Arduino programmed as a PS/2 to XT converter, but how can I get a way to get a monitor output? The hercules only output TTL video signals. I wondered if there was any way to convert that signal to something readable using common displays without modifying the display card. I found a few things online that may help, including this but I would need a digi-key order to get the parts, and the guys didn't even test it.
We know that your IBM 5150 has a serial port. If you have a 'modern' (or semi-modern) PC with a serial port, what you could do is:

1. Using an appropriate cable, connect the COM1 serial port of the 5150 to the COM1 serial port of the modern PC.
2. Modern PC: Run terminal software.
3. Modern PC: In the terminal software, set the parameters of serial port COM1 to 9600,N,8,1
4. 5150: Boot the 5150 with a DOS boot floppy, one that contains MODE.COM
5. 5150: (Blindly) Enter the command of: MODE COM1:9600,N,8,1
6. 5150: (Blindly) Enter the command of: CTTY COM1

The "CTTY COM1" gets DOS to direct 'console' output to the COM1 serial port (instead of the video card), and fetch 'console' input from the COM1 serial port (instead of the keyboard).

You now interact with DOS on the 5150 via the terminal software. There are limitations in what you can do, but at least it is something until a 'permanent' solution arrives.

reenigne
April 7th, 2016, 12:56 AM
I found a few things online that may help, including this (http://www.reenigne.org/blog/i-bought-an-xt/)

That was me! That hack worked fine for testing little assembly programs I wrote myself, but it was not useful for running existing software. Eventually I bought a CGA card and 5153 monitor on ebay. I also use old NTSC TV and a couple of different composite capture devices for looking at the composite output, and I have a VGA card that I use with it sometimes.

Unfortunately I can't think of a cheap/easy way to convert the normal output from a Hercules card to either NTSC or VGA - the timings are completely different so you'd need some complicated electronics to convert them. I did find https://www.dmcinfo.com/latest-thinking/blog/id/8626/creating-a-raster-monitor-from-an-oscilloscope which describes how to convert sync pulses to sawtooths for oscilloscope display but again the electronics is non-trivial.

Numitron
April 7th, 2016, 03:04 AM
I did not expect so many responses in so little time, I'm pleasantly surprised.
Anyway, I don't have actually anything to boot on, no floppies. I would love to be able to buy some to write on from my modern PC, but it seems that 5 1/4 drives are just impossible to install on any of my systems (my oldest modern PC is from 2005 or so) so I can't write a copy. Currently chasing down some boot disk on ebay, but they're expensive as hell. If any of you guys can provide a copy or anything in that regard, I'll be happy to pay the price.

I just expected to boot on BASIC and test basic functionality at first. Then get a boot disk and attempt to see if there is any problem with my current cards, floppy drives and HD.

And actually, reenigne, those electronics are totally doable for me (I like the challenge). Not trivial, but I could get the parts quick and cheap. I have access to pretty much all of the equipment I could ever want here and we even got a very nice lot of parts already. I must admit that my analog skills are not as good as I would like them to be, but I could be working on that next week, when I get the parts from Digi-Key.
Quickly going over that, I suppose that I eliminate the LM1881 since I got my pulse signal, and I don't even need to change my input pulse voltage? Hugh, I really need to get back to analog design.

Anyway, thanks a lot guys for your support.

Stone
April 7th, 2016, 03:53 AM
What boot disk are you (specifically) looking to get a copy of?

SpidersWeb
April 7th, 2016, 12:03 PM
If you're getting someone to send you a boot disk and have no means to create a new one.... I'd also order a drive cleaning kit to use first (or at least clean the heads with isopropyl / cotton buds). Nothing worse than inserting your only boot disk and having a dirty head tear the first track off.

Numitron
April 7th, 2016, 07:01 PM
Alright, so... Today was a good day despite the absurd weather. I repaired the motherboard (replaced the tant), got a satisfying 1 long beep followed by 2 small ones. Cleaned the unit as much as I could, then put it back together, testing one card at a time. The system post even with all cards inside, including RAM sixpak. However the hard disk was flashing an error code - 1101 which should be seek/recal error. I let the unit run for 90 minutes or so before doing hot starts to try to unstick the HD without disassembling the thing, but it still gave me an error. Only thing that changed was a new stepper grinding noise after spinup. I had the instinct of removing the drive of the unit, put it on its back and start it again to try to relief stress and unstick the head, and then the damn thing starts up without errors on the first try. I did a few power cycles then put everything back together. I start up the machine, and after post it attempt to boot from floppy A then attempt to boot from the HD. Finally, relief.
I quick probed the video output to see if it is outputting signal properly, and yeah, that looks like MDA sync signals as I could see from modem7's link. Pictures and HD fail video here (https://goo.gl/photos/QG2BZ8jdQ6UNnSL2A).

Now, to boot. I actually have a 5150 CP/M floppy going my way but of course I'm not sure I should start with that thing first... I'm not sure what I would like to boot on my machine to be honest. What are your recommendation? I thought PC-DOS or MS-DOS, but which version? My goal with this machine is pretty much to play around and try original software on it. My knowledge stops pretty much here. From where should I get a cleaning kit? Can I just wipe the head with IPA on a q-tip?

Again, thanks for the support!

modem7
April 7th, 2016, 10:41 PM
What are your recommendation? I thought PC-DOS or MS-DOS, but which version?
All I will say, is that on my IBM 5150/5160/5170's, I use PC-DOS (IBM DOS) instead of MS-DOS, just be more authentic, and the version that I have standardised on is 3.3
It works for me.
For hard drives over 32MB in size, I am forced to create multiple partitions, ending up with multiple logical drives (C:, D:, etc.), but I am not fussed about that.


From where should I get a cleaning kit?
I think aution sites are about it.


Can I just wipe the head with IPA on a q-tip?
Yes, but be careful.

Numitron
April 8th, 2016, 09:20 AM
What boot disk are you (specifically) looking to get a copy of?

From modem7's recommendation, I'm seeking a PC-DOS 3.3 boot disk.

Also, I will be seeking a CGA/EGA card with composite output as well as a RBBi monitor. Will post to proper section soon.

Stone
April 8th, 2016, 10:39 AM
From modem7's recommendation, I'm seeking a PC-DOS 3.3 boot disk. I like MSDOS 3.3 because it comes with GWBASIC.

Also, I will be seeking a CGA/EGA card with composite output as well as a RBBi monitor. Will post to proper section soon.I have a Datamedia CGA card with composite output:

30539

I have MSDOS and PC-DOS 3.3 disks as well. I prefer MSDOS because it comes with GWBASIC.

I don't know what an RBBi monitor is but I do have a Princeton Graphics systems HX-12 RGB monitor.

If there's any interest, lemme know.

Numitron
April 10th, 2016, 04:35 PM
*cough* *cough* *clear throats* ... Sorry, I meant RGBi, you know, CGA DB9-connector output.
I'm interested. I'll contact you.