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Old 30th Jun 2023, 10:03 pm   #21
Maarten
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

I have no experience with this system whatsoever, but if I interprete correctly, you're forcing it to send out a 32kHz sync signal by setting forced_scandoubler to 1. Just try setting it to 0 and see if that helps.
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Old 3rd Jul 2023, 11:48 am   #22
PenroseHouse
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

Thank you, Maarten, that does work:
forced_scandoubler=0
composite_sync=1
ypbpr=0
direct_video=0

...except:

1 the image is wobbly, and has top-right corner sort of folded over, I could take a photo but

2 it only works on the menu screen, then when I choose a game/core these settings seem to be overriden and we get junk again.

...so I probably need to talk to someone who is an expert in the MiSTer to find out about how to force the settings to apply to every game, every core, rather than just the menu.

Maybe there's two problems, and 1 above is something to do with capacitors or whatever, if I can solve 2 and I still get 1 I'll post a photo.

...

Actually, the MiSTer works with my Dell CRT.

I need Windows PC on one CRT and MiSTer on the other, at the same time, and I no longer care which is which!

So I could alternatively use my newer Dell CRT with the MiSTer, and get the Amstrad monitor working with my Windows PC.

Maybe I need to buy an RGB graphics card, my graphics card only has HDMI and DVI-D - or maybe the Amstrad CM14 can be connected to the DVI-D.

Rather use analogue as much as possible to avoid distorted pixels.
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Old 23rd Jul 2023, 2:14 pm   #23
PenroseHouse
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

Progress...?

I bought an adapter on eBay, converts the MiSTer's VGA output to RGB, has VGA socket the MiSTer end, SCART the monitor end, plugged into the SCART->Amstrad adatper.

Output is now stable, but as you can see there's 2 (3?) significant issues:

1 right is to the left, left is to the right, right VERY dark
2 top is distorted
3 (whole image is a LITTLE dark/off colour ---- maybe!)

Of course the diagonal lines aren't there in real life.

I have these settings as suggested by the seller:
forced_scandoubler=0
ypbpr=0 ; set to 1 for YPbPr on VGA output.
composite_sync=1 ; set to 1 for composite sync on HSync signal of VGA output.
vga_scaler=0 ; set to 1 to connect VGA to scaler output.

and settings as below left on default. Note that I'm using the MiSTer Multisystem which has a few physical switches:
-sync on green and/or multisync crt (applies to both VGA and SCART output)
-a related switch: "Standard position (Option link jumper pins 1+2) / Alternative position (Option link jumper pins 2+3)"
-4:3/16:9 set to 4:3
-5volt/3.something (can't read it) volts, have only tried the lower voltage
(I am UK/PAL)

Once again, really grateful for any help. Maybe the monitor is just faulty?

______________
Those settings left as default:
vscale_mode=0 ; 0 - scale to fit the screen height.
; 1 - use integer scale only.
; 2 - use 0.5 steps of scale.
; 3 - use 0.25 steps of scale.
; 4 - integer resolution scaling, use core aspect ratio
; 5 - integer resolution scaling, maintain display aspect ratio
vscale_border=0 ; set vertical border for TVs cutting the upper/bottom parts of screen (1-399)
rbf_hide_datecode=0 ; 1 - hides datecodes from rbf file names. Press F2 for quick temporary toggle
direct_video=0 ; 1 - enable core video timing over HDMI, use only with VGA converters.
vga_sog=0 ; 1 - enable sync on green (needs analog I/O board v6.0 or newer).
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Old 23rd Jul 2023, 11:54 pm   #24
SiriusHardware
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

Which way 'up' is the composite sync being generated? Idle High / Active Low, or Idle Low / Active High? Can you change that 'polarity'?
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Old 24th Jul 2023, 1:26 pm   #25
PenroseHouse
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

I feel bad pasting all this stuff in below but I'm an assembly coder, not a hardware guy! Really grateful for any help.

I've attached the MiSTer.ini file, but here are the options that I think MAY have something to do with what you're asking me (am UK Pal):
--------------------------------------------------
vsync_adjust=0
; Set to 1 for automatic HDMI VSync rate adjust to match original VSync.
; Set to 2 for low latency mode (single buffer).
; This option makes video butter smooth like on original emulated system.
; Adjusting is done by changing pixel clock. Not every display supports variable pixel clock.
; For proper adjusting and to reduce possible out of range pixel clock, use 60Hz HDMI video
; modes as a base even for 50Hz systems.
--------------------------------------------------
; If you monitor doesn't support either very low (NTSC monitors may not support PAL) or
; very high (PAL monitors may not support NTSC) then you can set refresh_min and/or refresh_max
; parameters, so vsync_adjust won't be applied for refreshes outside specified.
; These parameters are valid only when vsync_adjust is non-zero.
refresh_min=0
refresh_max=0
; These parameters have the same format as video_mode.
; You need to supply both PAL and NTSC modes if you want vsync_adjust to switch between
; predefined modes as a base. This will reduce the range of pixel clock.
;video_mode_ntsc=0
;video_mode_pal=7
--------------------------------------------------
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Old 24th Jul 2023, 1:27 pm   #26
PenroseHouse
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

Not sure the file attached.
Attached Files
File Type: txt MiSTer.ini___.txt (14.0 KB, 41 views)
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Old 24th Jul 2023, 2:18 pm   #27
SiriusHardware
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

Well, perhaps an easier way to address the question is: If you put a scope on the SYNC output signal going to the monitor, is it active low (normally high, with low going pulses) or active high (normally low, with high going pulses?).
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Old 28th Jul 2023, 1:04 pm   #28
PenroseHouse
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

I admit to being completely out of my depth here. I have one of those things that you touch the two ends and it bleeps, and numbers appear on the screen! I'm totally not a hardware guy so I feel like I'm wasting people's time on here, for which I apologise.
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Old 28th Jul 2023, 1:13 pm   #29
SiriusHardware
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

You aren't, it's just that the MISTer (which I understand is a hardware emulator of multiple systems, especially old computers) is a bit of a niche interest here and not many people know about it. I am aware of it but I don't have one, nor have I used one.

Have you found this forum yet?

https://misterfpga.org/

It seems dedicated to the MISTer. You may find some more knowledgeable people there. Sorry to seem less than usually helpful.
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Old 28th Jul 2023, 4:23 pm   #30
PenroseHouse
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

Thank you, I shall post on there.

I'm also keen to connect this monitor to a Windows PC, but my understanding is that it's very complicated, you need:

- to install an (old) RGB graphics card
- to make your own cable
- to install special software and tweak it (I'd tie myself in knots just with this last one)

If I happen to be wrong and there's an easy way, perhaps someone could tell me. But if I'm right and it's that complicated, I think it's best not to get into it!
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Old 1st Aug 2023, 2:14 pm   #31
PenroseHouse
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

OK, I posted on the FPGA forum, got some really helpful replies, but tried all the options and, although I get a BEAUTIFUL picture, when I'm playing a game and the border turns white, yellow or bright green, anything white turns purple!

This is surely a MiSTer issue, though I mention it here in case I'm wrong and it could be eg capacitors need changing, if that's possible perhaps someone can let me know.

So we can consider this matter resolved, and someone can lock the thread if that's what you do on here...?

Though if anyone knows how to make a CM14 work with a Windows PC, please reach out!


...


Just adding some closing words purely for anyone who found this thread because they're considering buying a CM14 to use with a MiSTer:

It looks like due to some complications with the MiSTer, it simply isn't compatible with the CM14.

Either the MiSTer thinks it's detecting some problem and (wrongly) changes some colours to allow for it, or the monitor does the same. Or else (as someone suggested) there's some voltage compatibility issue between the MiSTer and the monitor...?

Either way, don't buy a CM14 to use for a MiSTer monitor unless you're a serious hardware guy/girl and are willing to risk time and money.

As for me - at least I know the monitor isn't faulty, so at some point I'll buy a real Spectrum, to use with the cable from Cool Novelties - I assume that cable works.

In case anyone does want to try a CM14 with a MiSTer, I might as well post the final .ini options here, though this is ultimately MiSTer stuff, and as I say the whites can look like your favourite white Fruit of the Loom T-shirt when you've accidentally left a red sock in the washing machine...

____________________________________

;ypbpr=0 <----delete as no longer used

forced_scandoubler=0 <----it's a 15Hz monitor so don't double 15 to 30

composite_sync=1 <----don't know why but FPGA forum guy told me this

menu_pal=1 <----it's a PAL monitor, with 0 you'll get a flickering main menu

vga_sog=0 <----try the four combinations of 1/0 here vs. physical SOG switch on/off,but all seem to mean green/purple issues at least some of the time

vga_mode=rgb <----supported modes: rgb, ypbpr, svideo, cvbs. rgb is default.
(this last option is completely new so paste it in if it's not there)
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Old 3rd Aug 2023, 2:13 pm   #32
PenroseHouse
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

Is there a way to connect this monitor to my SCART (presumably composite) Pioneer VHS video player?

If it's a rabbit hole then I won't bother but if there's a cable on Amazon or eBay that I can just buy then that would be great.
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Old 4th Aug 2023, 3:12 am   #33
atsampson
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

You wouldn't just need a cable - the monitor doesn't include the hardware needed to decode composite video to RGB and syncs. Amstrad did sell an add-on box that sits under the monitor and provides a TV tuner and composite decoder, so you can use the monitor as a TV - the (splendidly named) Amstrad MP-3 - but they're not very common.
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Old 4th Aug 2023, 8:06 pm   #34
Maarten
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

Philips made similar add-ons for their monitor range. Also not too common, but I've seen a few over the years.
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Old 4th Aug 2023, 8:42 pm   #35
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

The Amstrad add-on was sold by surplus mail order companies about 30 years ago so there must be some about, though many will have been dismantled and repurposed.
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Old 8th Aug 2023, 10:51 am   #36
PenroseHouse
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

Thanks for that. It looks like there are TWO (or same listed twice) on eBay, in France, but it's like seventy quid, if it let me solve the other problem too I'd try it but not sure I can do that right now.

Though it's French, has French text on the buttons, would it work on the monitor? Is French electrickery the same...?

AMSTRAD
Adaptateur MONITEUR MODELE MP-3
12 volts
Connecteur péritel connecteur coaxial câble alimentation et sortie RVB
Norme L SECAM
testé, fonctionnel et en bon état cosmétique
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Old 8th Aug 2023, 11:57 am   #37
Maarten
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

The way I understand it, is that it has a SCART input. It should work fine for converting SCART to your monitor input. The mains voltage for France was 220V back in the day, so you might want to wire up a small 24V transformer to use as a voltage dropper (secundary in antiseries with the mains).
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Old 8th Aug 2023, 2:33 pm   #38
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

The French one probably won't work. It says system L, SECAM on it, so unless the VHS player can output this standard on its RF output (it won't, unless it's French) you won't get a picture or sound from a UK-spec machine. Better to search for a UK model MP-3 which supports system I (or B/G) PAL.

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Old 8th Aug 2023, 4:17 pm   #39
Maarten
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

Video and sound through the SCART should work, but I overlooked that the TS wanted to use a VHS player as a source. CVBS (composite video signal with colour) won't work as the VHS player gives out a PAL signal and the tuner unit expects a SECAM signal.

However, a DVD player will work correctly as long as you set it to output RGB.
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Old 9th Aug 2023, 4:47 pm   #40
PenroseHouse
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Default Re: Amstrad CM14 CRT computer monitor - blank screen

Maarten, cmjones01, THANK YOU both for your input on this. I shan't risk it. Maybe I can get the VHS player to work on my newest old CRT, an Elonex from 2001, but that's totally off topic because it's a different monitor.

BTW, it works a treat with the MiSTer as it's VGA.
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