Amiga Tower display problems

[technium]

I brought a 2nd hand amiga tower off ebay awhile ago and it worked when I first tried it and then I changed the screen resolution and restarted and now I get nothing but a white screen with the flat screen monitor connected to one port or "no Signal" if I connect the monitor to the other port.

I know its got one of those scan doubler things but I just cant get any display at all apart from this white screen. Any help?

thanks

Colin

[amigakit]

Welcome to Amiga.org!

Connect the Scandoubler SVGA port to the TFT for the following... As a fall back, connect the Amiga to a TV

Reset the Amiga, hold down both mouse buttons for up to 30 secs until an Early Startup Menu appears - select boot with no startup-sequence

at the command prompt 1> type:

rename sys:prefs/env-archive/screenmode.prefs sys:prefs/env-archive/screenmode.old

Then reset the Amiga and go into Workbench.  Goto prefs drawer and run Screenmode.  Select the previous working graphics card screen then test on the TFT to see if working.  If OK save the settings.

 

[Boot_WB]

Is the scandoubler the internal type which clips over some of the chips on the motherboard?  Or an external one?

Are you using some other form of graphics card aswell (eg a Zorro card, or a pci card?)

Does it still sound like the computer is booting from the hard-drive?

Try connecting the (yellow) composite out to a composite in on your TV (a standard phono--phono lead should do the trick).  See if you get a signal from that.  If you can boot into workbench on that you can just reset the screenmode to whatever it was before.

[technium]

ok cant even see what a scan doubler is, the two connections for the monitor (pc monitor btw) is one that goes into a 3dfx graphics card - this is the one that displays "no signal" and the other one is a monitor connector which has a ribbon cable which goes onto the motherboard but theres loads of stuff in here, Ive just removed the graphics card, tv card and network card but theres also a Mediator PCI 1200 SX which lays on top of motherboard which all these cards connect into other than that I cant really see what im looking for

[technium]

ah ha, now ive got it booting, I removed all the cards and mediator and nothing happened when turned on, so reseated mediator (no cards) and now im into workbench although resolution is pants so how do I change that?

Next is to try installing each card one at a time.

[technium]

ok reseated the cards one at a time and it all works fine, upto the point I installed the 3dfx card so why would that be?

any advice, been ages since I had a miggy and that was a A1200

thanks

[technium]

ok next update, I can get it to power on with the 3dfx card inserted but with the power cable not plugged into it.

Ive also found wbprefs on the workbench to change resolution but it keeps saying to close all windows but none are open apart from the main workbench one, so need some advice on that, also whats a suitable resolution for 15" flat panel pc monitor?

thanks if your still reading.

[Boot_WB]

Background (in my limited understanding):

The amiga's native RGB monitor output is at 15.5kHz.  PC monitor frequencies are generally somewhere between 30 and 100kHz.

Original amiga monitors accepted video input at the frequeny the amiga produced - 15.5KHz.  Later 'multiscan' monitors accepted frequencies between around 15.5 and 50 KHz, allowing both PC and amiga to share the same monitor.  Modern PC monitors are generally some range between 30 and 100 kHz, so 'original' amiga screenmodes will not be displayed on them.

The amiga is capable of producing screenmodes at 30khz (-ish), but it takes its toll on processing (and, bizarrely the serial port baud rate).  

Step in the scandoubler, stage left: the scandoubler takes the amiga's native 15.5kHz signal and doubles the scanrate to 31kHz with no extra overhead on the amiga's chipset.

You may know all this already, so apologies if you feel patronised.

To change screen settings:

Go into your workbench drive, prefs drawer, double-click screenmode.  The graphics card you're using in your mediator is a voodoo (3, 4 or 5 - it makes little difference at this point).  
You want to choose one if the screenmodes which start with VOODOO, eg VOODOO:1024x768:32-bit - will give you 32 bit (aka truecolour) 1024x768 resolution through the mediator/voodoo card.  I've found 24-bit (aka high colour) works quite a bit faster, and the colour difference is not really noticable.

If you choose a screenmode labelled with just the numbers (eg 640x320) this will display through the amiga AGA chipset (it will output the video signal through the 23-pin RGB connector next to the composite out port.  If you have a scandoubler attached it should output these 'native' AGA screenmodes through the scandoubler port aswell at twice the frequency, so normal 15.5KHz screenmodes will come out as 31KHz.

There may be other monitor modes available aswell (eg starting with DBLPAL, PAL, NTSC or DBLNTSC): PAL, NTSC you may be familiar with; DBLPAL DBLNTSC are the ~31kHz screenmodes produced by the amiga chipset (as discussed above)  - note these will NOT be doubled to 62kHz by the scandoubler - they will just be passed through.  they will still exact a heavy toll on your chipset though.

Hope that helps, and is not too inaccurate.  

[motorollin]

When you boot the Amiga it will try to initialise the 3Dfx card in the Mediator. If it is not there, then it will not use it, and the Amiga's display will be used. That's what is happening now. When you connect the 3Dfx card to the Mediator it displays through that. From the sounds of it, you have selected a screemode that either your 3Dfx card or your TFT screen are unable to display. Follow Amigakit's instructions in the second post of this thread to reset your display settings back to their defaults. Then boot up with the 3Dfx card connected and select the resolution you were using before when it worked.

--
moto

[technium]

Thanks for the info, Ive just loaded up workbench, then prefs, then screenmode but I dont have much there.

I have the following under display mode

1280x256
320x256
640x256
plus each one has a interlaced option.
Then mode propertied which is screen size and stuff and then colours is a scroll bar but at maximum its only on 256 then the option to test, save, use or cancel and thats it.

How come I dont have the voodoo ones like you suggest

[motorollin]

Sounds like the Voodoo install is screwed - there should be loads of screenmodes. Have a look at the Mediator install guide on the CD. It will tell you how to install it properly. Once this is done all the screenmodes should be available in ScreenMode prefs.

--
moto

[technium]

what cd are we talking about, the only one I got is the os cd and thats it, I dont have no install disks for mediator or 3dfx card

Are they downloadable from the net and if so would a pc made cd be readable on this amiga?

[motorollin]

You can't download them unfortunately. You have to get them from Elbox. They come on a yellow cd with "MMCD" in red writing on it. The person you bought the Amiga from might have it.

--
moto

[technium]

that was ages ago what does mmcd stand for?

Ive just looked in the prefs folder and I have one called "Picasso96Mode" and when I open it it has settings for "voodoo Village-31" where you can choose 1024x7638 etc etc and under modes  you can have
256colours 31khz 74Hz
HiColour 71khz 85Hz
truecolour 30khz 36hz
truealpha 71khz 85 hz

So could this be the right place?

[motorollin]

MMCD stands for MultiMedia CD and it comes with the Mediator.

You've got a Voodoo screenmode in P96Prefs which is good, so you may not need the CD after all. If you click the button to test the screenmode, can you see the testcard on the monitor connected to the Voodoo?

--
moto