C4PMF not working

MK14HAK
Posts: 356
Joined: Wed Mar 16, 2011 1:49 am
Location: New Zealand

Re: C4PMF not working

Post by MK14HAK »

PS
"If it hangs booting tk0 check controller TX/RX CLK/DATA timing adjustments and particularly the data separator timing as this is CRITICAL and an minor miss adjustment here means go no go."

First note the position of the data separator trim pot.
Then make a very minor adjustment either side of this. You may suddenly find the head unloads and you are back at the monitor prompt - its loaded tk0 !
If not then check your timing.
Good luck.
600RevB:16K,2MHz,64x32,470,CEGMON
SuperKit:502,540B,542B,CEGMON, 8" and 5" FDDs
Cards:PE IO,6522 D-A-D, AY3-8910,ProgramGraphics,Color,UK101
WIP:HexDOS,FDD Emulator
Jeff
Posts: 370
Joined: Fri Mar 07, 2014 4:44 am
Location: British Columbia, Canada

Re: C4PMF not working

Post by Jeff »

Today, I reached a milestone on this project.

For the first time, I am able to boot from floppy and have an OS running on the machine!
C4PMF Boot Screen.jpg
C4PMF Boot Screen.jpg (127.89 KiB) Viewed 12534 times
It has been an arduous task to reach this point. I have learned an immense amount and really enjoyed it!

Whats Left?
- Build a cool enclosure for the floppy, or use the original,,,not sure which direction to go.
- get nice video out from the computer... Right now the signal sucks, and is full of interferance.
- get the color video output working
- fix the right shift key..... it works only sometimes. I will probably replace all the key switches. And when I have all the originals off, I will take some detailed photos of the board. Maybe someone will replicate it!
- figure out the high-resolution graphics video!

Thanks Everyone for all your help, especially Dave, Steve, Phil, Mike, and Grant! Without your help, this computer would be in an electronic recycling dumpster.

/Jeff
Image
Jeff
Posts: 370
Joined: Fri Mar 07, 2014 4:44 am
Location: British Columbia, Canada

Re: C4PMF not working

Post by Jeff »

Hi All,

I would like to improve the video signal on my C4PMF. And of course, I know nothing (well, almost nothing) about video signals and how they are generated etc. If you take a look at the screen shot in the previous post, you can see "snow" in the black background, and also, the signal itself is quite weak. I am using a modern LCD flat panel to display the image and it does a nice job with my other computers, so I don't think it would be the source of the "snow". I have replaced the old rusty RCA jack on the back of the unit and I am using a good quality video cable.

Does anyone have any suggestions on what I can check?

Oh, also, Im not getting colour, just shades of grey...(and definitely not 50 of them!)

Thanks in advance.
/Jeff
Image
MK14HAK
Posts: 356
Joined: Wed Mar 16, 2011 1:49 am
Location: New Zealand

Re: C4PMF not working

Post by MK14HAK »

How does it look on CRT monitor Jeff ?
600RevB:16K,2MHz,64x32,470,CEGMON
SuperKit:502,540B,542B,CEGMON, 8" and 5" FDDs
Cards:PE IO,6522 D-A-D, AY3-8910,ProgramGraphics,Color,UK101
WIP:HexDOS,FDD Emulator
BillO
Posts: 216
Joined: Tue Jul 08, 2014 4:03 pm
Location: Canada
Contact:

Re: C4PMF not working

Post by BillO »

A lot of the modern monitor/TV sets load the video line with 75 ohms. This is technically correct for most 'real' video applications. However, back in the day, this was not adhered to on most computer based monitor systems. The video on most old systems (including OSI) back then used 7400 series logic chips to produce the video. Unfortunately, they can't sufficiently drive a 75 ohm load (maybe about 150 ohms). They can get closer than, let's say - on a 600 board - but can't really do the job 100%. Today's monitors are impedance matched and digital (read - have no sense of humor).

One of the things I want to try is making the video better on my 600 boards. Not sure when I'll get to it, but I'll see what I can get out of a 7403 for sure. What chip/circuitry is used in the C4P as a video driver?

If they ever made a 74ACT03 (or even better 74ABT03), that would be the ticket for the 600 boards!!!
Box stock Superboard II Rev. B
KLyball replica 600D, replica 610 & KLyball Data Separator
OMS SBME and SBME+ memory cards
OMS Digi-Mule expansion bus
KLyball memory card
MK14HAK
Posts: 356
Joined: Wed Mar 16, 2011 1:49 am
Location: New Zealand

Re: C4PMF not working

Post by MK14HAK »

If the noise is still evident on a CRT then it could be the mux of video and cpu access with VAS at U56 on a RevB and D
Connect 02 clk from CPU to U56-2 after cutting trace to U56-2.
Apply the same technique to a 540B- maybe at U6F-2 and check C36. (Untested)
Impedance mismatch will cause signal degradation as per Bill. Maybe a discrete transistor emitter follower would have been better ? (Those 7403 s often blow I found.)

Mike
600RevB:16K,2MHz,64x32,470,CEGMON
SuperKit:502,540B,542B,CEGMON, 8" and 5" FDDs
Cards:PE IO,6522 D-A-D, AY3-8910,ProgramGraphics,Color,UK101
WIP:HexDOS,FDD Emulator
Jeff
Posts: 370
Joined: Fri Mar 07, 2014 4:44 am
Location: British Columbia, Canada

Re: C4PMF not working

Post by Jeff »

BillO wrote:What chip/circuitry is used in the C4P as a video driver?
C4P Video Output.jpg
C4P Video Output.jpg (69.3 KiB) Viewed 12465 times
With my limited electronics background, I would be suspect of the 2N5225 transistor.

/Jeff
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Jeff
Posts: 370
Joined: Fri Mar 07, 2014 4:44 am
Location: British Columbia, Canada

Re: C4PMF not working

Post by Jeff »

MK14HAK wrote:If the noise is still evident on a CRT
I have to find a CRT.... those things are rarer than OSI computers!

MK14HAK wrote:it could be the mux of video and cpu access with VAS at U56 on a RevB and D
Connect 02 clk from CPU to U56-2 after cutting trace to U56-2.
That is actually my next project as the video output of my Superboard also has issues.... it occasionally "quivers", I will have to learn how to post videos!
MK14HAK wrote:Apply the same technique to a 540B- maybe at U6F-2 and check C36. (Untested)
Impedance mismatch will cause signal degradation as per Bill. Maybe a discrete transistor emitter follower would have been better ? (Those 7403 s often blow I found.)
"Discrete transistor emitter follower" sounds really technical to me :shock:

I will investigate U6F-2 and C36.

Thanks Mike!
/Jeff
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Jeff
Posts: 370
Joined: Fri Mar 07, 2014 4:44 am
Location: British Columbia, Canada

Re: C4PMF not working

Post by Jeff »

Like this?
02 to U6F-2.jpg
02 to U6F-2.jpg (227.75 KiB) Viewed 12464 times
/Jeff
Image
BillO
Posts: 216
Joined: Tue Jul 08, 2014 4:03 pm
Location: Canada
Contact:

Re: C4PMF not working

Post by BillO »

That is a discrete emitter follower and should be able to work fairly well.

Have you tried adjusting R5 and R9?

R10 will control the amount of color. Make sure you try that too, and see if the signal at pin 5 of the chip on the upper left is making it to the mixer base.
Box stock Superboard II Rev. B
KLyball replica 600D, replica 610 & KLyball Data Separator
OMS SBME and SBME+ memory cards
OMS Digi-Mule expansion bus
KLyball memory card
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