Getting a display from Apricot computer

[roadrash]

I recently with the help of the power supply section of these forums, repaired and restored a vintage Apricot-PC. When I got the computer I was'nt given a monitor with it and as I have many other systems and monitors I didnt expect to have problems. As it turns out this particular computer came with its own dedicated monitor and from the circuit diagrams it seems its a video (not RGB/VGA) output of some type yet I have been unable to get a display on any low resolution video monitor. There are only 4 connections on the monitor cable 1:Ground, 2: Horizontal Sync, 3:Vertical sync, 4:Video. When i recently made a cable and connected to a old phillips video monitor with the very same connections it gave me me a display of some kind continually scrolling and ratcheted down each side. No text could be made out. I wonder could someone help me solve what display is neeed for this computer. I have uploaded the service manual which also covers the monitor with schematics that might off some clues.

[Andrew F. Ali]

Re: Getting a display from Apricot computer

The Vertical Sync is out. Try adjusting the V-Hold on the Monitor to stop the scrolling. If the Monitor was working before then there may be e-caps in the PC that may need replacing.

[R_J]

Re: Getting a display from Apricot computer

If you have a vertical sync problem but you have the sync signal going from the computer to the monitor it's a good chance it has the wrong polarity and the signal would need to be inverted.
That monitor in the diagram requires positive going horizontal and positive going vertical sync so thats what the computer must be outputing, what is the model of the philips monitor you are using?
The diagram I provided would only need one inverter section for each sync signal and not be configured to compine the signals

[roadrash]

Re: Getting a display from Apricot computer

If you have a vertical sync problem but you have the sync signal going from the computer to the monitor it's a good chance it has the wrong polarity and the signal would need to be inverted.
That monitor in the diagram requires positive going horizontal and positive going vertical sync so thats what the computer must be outputing, what is the model of the philips monitor you are using?
The diagram I provided would only need one inverter section for each sync signal and not be configured to compine the signals

Took a while but found a service manual (attached) for the phillips monitor I was using to try it on. It should give all the info we need. I have other monitors but they dont have a video input that matches the computer like this one does.
Can you check (page 15 of this manual and see if this one should work. I currently use this monitor on a Commodore PC1 so know it works, just be nice to get it to work with this Apricot too.

[R_J]

Re: Getting a display from Apricot computer

That monitor requires negative going sync for the vertical, the sync pulse will need to be inverted before going to the monitor,
It may be posible to mod ic601 in the monitor to change the sync polarity (ie lifting pin 5)
you could install the 74c04 into the monitor feeding the v sync from the plug into pin 3 and the output of 74c04 pin 4 into ic601 pin 4 and getting +12 for the ic from the monitor itself

[dick_barton]

Re: Getting a display from Apricot computer

Looking at Page 164 of BM7913.pdf, both the Horizontal & Vertical sync are given as Positive (+)

Apricot manual says Horizontal sync is Positive (+) and Vertical sync is Negative (-)

So I would build the neat convertor R_J has given in post #3

[roadrash]

Re: Getting a display from Apricot computer

Looking at Page 164 of BM7913.pdf, both the Horizontal & Vertical sync are given as Positive (+)

Apricot manual says Horizontal sync is Positive (+) and Vertical sync is Negative (-)

So I would build the neat convertor R_J has given in post #3

WOW thanks so much everyone. I will do this Just a question I cant seem to find any 74C04 ic's

[roadrash]

Re: Getting a display from Apricot computer

That monitor requires negative going sync for the vertical, the sync pulse will need to be inverted before going to the monitor,
It may be posible to mod ic601 in the monitor to change the sync polarity (ie lifting pin 5)
you could install the 74c04 into the monitor feeding the v sync from the plug into pin 3 and the output of 74c04 pin 4 into ic601 pin 4 and getting +12 for the ic from the monitor itself

Think I have managed to source all the components now. I may need a little bit of help with this first need to find a old bit of vero board or something. I am a little confused with the 74C04 layout on your diagram as its different to what is shown online. See attachment. Can you explain?

[R_J]

Re: Getting a display from Apricot computer

I think this should work as its only the vert. sync pulse that needs inverting. That diagram was for inverting and combining the h & v sync for a different monitor
this is done inside the monitor and uses the +12 volts from the monitor so the diodes and cap. are not required, it should work

It may have been possible to copy the circuit used for the video inversion (ic601 pin 9)
By lifting pin 5 from ground and connecting it to +12 via a 10K resistor and adding the diode and a small value cap.

[R_J]

Re: Getting a display from Apricot computer

Have you been able to get any video to display even with the vertical sync issue? I see this monitor has a seprate video and intensity input, what was it used for before?

[roadrash]

Re: Getting a display from Apricot computer

Have you been able to get any video to display even with the vertical sync issue? I see this monitor has a seprate video and intensity input, what was it used for before?

yes here is a picture of what i am getting and you can see the ratchet/saw tooth pattern. i am not connecting intensity as computer doesnt output that. an i right in asuming this old 1980 is anologue output? may i am using the wrong monitor

[R_J]

Re: Getting a display from Apricot computer

Is that with signal going to the monitor? You could try adjusting the horz. frequency, R517, If the horz. osc. is off frequency the display could look like that.
Looks like the monitor horz. frequency runs at 18,432Hz the computer outputs 15,750 so there is quite a difference and I'm not sure if can be adjusted that low to sync the horz. frequency, looks like the range is 17,298 - 18,694 Hz

If those sawtooth go away when the horz. input signal is removed, then the monitor is trying to sync to it but can't, You could try changing R514 from 15K to 12K (as per data sheet for TDA2593) and see if that will bring it in

[roadrash]

Re: Getting a display from Apricot computer

Is that with signal going to the monitor? You could try adjusting the horz. frequency, R517, If the horz. osc. is off frequency the display could look like that.
Looks like the monitor horz. frequency runs at 18,432Hz the computer outputs 15,750 so there is quite a difference and I'm not sure if can be adjusted that low to sync the horz. frequency, looks like the range is 17,298 - 18,694 Hz

If those sawtooth go away when the horz. input signal is removed, then the monitor is trying to sync to it but can't, You could try changing R514 from 15K to 12K (as per data sheet for TDA2593) and see if that will bring it in

I appreciate this but concerned about modifying a monitor for this computer. I use this on other machines and dont want to change just to use on this Apricot computer. Would it be better if I picked up one of these NEC multisync monitors with all the various inputs and I also have have herw something else that we might be able to use, that i bought in case there ever was a problem like this. I am talking about this video converter http://www.ebay.co.uk/itm/New-RGB-CG...wAAOSwu1VW8Rwk.
If we could use this thing it would be a better option. Ive had this for a few years but not as yet found a use for it. What do you think?

[roadrash]

Re: Getting a display from Apricot computer

Just bought a second hand NEC Multisysnc 1810 which according to the manual does Sync polarity which is what we are looking for I believe. If this works it would be be great and seeing as it was only £20 it will be a bargain and very useful in the future as well.

[R_J]

Re: Getting a display from Apricot computer

is this the one?
on page 39 "Synchronisation Range - Horizontal 24.0 kHz to 80.0 kHz (Automatically)"
your computer outputs 15.750 khz horzontal, so it still might not sync

[roadrash]

Re: Getting a display from Apricot computer

is this the one?
on page 39 "Synchronisation Range - Horizontal 24.0 kHz to 80.0 kHz (Automatically)"
your computer outputs 15.750 khz horzontal, so it still might not sync

yes spot on thats it. It came today and ive tested it on a pc and its all working. i looked the manual and it does say it will accept both Horizonatl and vertical sync in both positive or negative. This is wht i bought it. I still cant see where i connect the computers video output to on the monitor as it only mentions R G & B and not composite or anything else. But does tell me where to connect vertical and horizontal sync.

[roadrash]

Re: Getting a display from Apricot computer

i also have one of these maybe we could use bothhttp://m.ebay.co.uk/itm/Genuine-GBS-...%257Ciid%253A4

[R_J]

Re: Getting a display from Apricot computer

yes spot on thats it. It came today and ive tested it on a pc and its all working. i looked the manual and it does say it will accept both Horizonatl and vertical sync in both positive or negative. This is wht i bought it. I still cant see where i connect the computers video output to on the monitor as it only mentions R G & B and not composite or anything else. But does tell me where to connect vertical and horizontal sync.

You can connect the video from the computer to the green input of the monitor

[roadrash]

Re: Getting a display from Apricot computer

I just managed to persuade someone to sell me a monitor from a non working Apricot system he was selling on Ebay and when it arrived yesterday I stripped it apart to check if anything was gonna blow when I tried it and it worked OK. Its a really tiny little monitor here are some pictures of it inside etc. So at lease i dont have to worry about trying to get something else adapted for use with it now and I now know for sure the computer itself is working properly too as its shows a picture of a floppy on screen asking to insert a disk.