MacOSMonkey
Well-known member
Does anyone have v.1.3 of the Spectrum/8 Series III ROM?
- So do I need a different oscillator to run 1024x768 at 60hz for different manufacturers? I have a Dell e153fpc lcd monitor (native 1024x768 at 60 and 75) and I can’t seem to get it to work right. The card is a series III and has the 30.24, 64, and 80 MHz oscillators, with one empty slot.
With the Spectrum/24 Series III, the problem may be that you are using the board in a non-cleared slot. Make sure you clear the slot PRAM before trying the board so that it will go into Round Robin by default (cycling configuration choice where you hit the space bar to set the config) at startup. Boot the machine with nothing in the slot, then insert the board, or zap PRAM on the Mac. Or, as I recall, you can also hold down the option key at power-on to initiate Round Robin.
Another problem may be the response time of the monitor, which may be slower than the time allowed for each sync config in Round Robin. You can try configuring the board at whatever mode you want on the other monitor, then plug in the Dell FP and see if it can sync up. The Dell monitor may be a little bit pokey on sync detect, depending on the output timing. (?)
If neither of those things helps, then you may not have the right sync output via the DB15->VGA adapter. The board obviously works, since it is working in your other config. Or, maybe the timing is out of spec for the Dell for some reason. You would need to look at the output signal on a scope.
The SuperMac stack probably isn't going to help you with this one -- also it predates the Spec/24 III.
Sometimes it is the types of sync - not all monitors support Sync on Green.So sounds like even though two panels are at the same resolution, same V/H frequencies, same nominal clock frequency, there are some differences that cause it not to work on certain systems?
Yes, if the card is in a slot it was not in before, it does that round robin thing (same when you zap the PRAM). And yup, you're right, it also does it if you hold down the option key on power on. But I believe all this does is allow you to choose the monitor/frequency and is useful if you only have one monitor. If you are able to boot, I think you get the same effect by opening the SuperVideo control panel and choosing the monitor manually and choose "Install", and then rebooting? or am I wrong?
So sounds like even though two panels are at the same resolution, same V/H frequencies, same nominal clock frequency, there are some differences that cause it not to work on certain systems?
Sometimes it is the types of sync - not all monitors support Sync on Green.
If you are trying to convert DB15 -> VGA and you are getting no video, you will probably need an adapter with dipswitches that lets you manipulate how sync is being transmitted. They are available, I think. That may get it working. You should also look up the tech specs for the Dell and see what it requires. (Regardless, it obviously works in your other configs, so whatever it expects, it is not getting and it is likely a sync issue.)
Hmm...since you have a scope, compare the sync width and shape between the PC-8 and Spectrum/24 III. The rework cap on the Bt output that is bent over the top of the part on Spec/24 III (which I think is on green - but check the pins) is there to minimize vertical line shadowing (voltage ringing/overshoot). The cap doesn't completely eliminate the problem, but it fixes it beyond the threshold of general user awareness/detection. So, maybe the sync is out of spec vs. the Dell monitor requirements, or maybe the cap is affecting the waveform in a way that prevents it from syncing (it's going to round it off and, therefore, shorten the valid high period). The video signal is obviously present and functional based on the other monitor you have, so it must be some spec/voltage issue. Maybe the Dell FP is more sensitive to deviations and requires longer to sync up. The problem might also relate to other aspects of the video timing (blanking, etc.). As a quick test, you could try just removing the cap to see if that changes the behavior, but there will be increased vertical ringing in the video output visible as shadowing on high frequency color changes -- like the black and white borders of folders, etc.I've been using a DB15->VGA adapter with 10 dip switches. I've been keeping a notebook trying every combination. I think I exhausted it for the Spectrum III / DELL combination with no success.
I also tried with a Radius PrecisionColor 8 (not 8XJ) and it worked with the DELL at 640x480 using 1467 which is 13" 640x480 @ 66Hz Mode 5 (sync on green) albeit scaled up (native resolution on the DELL is 1024x768 from 60-75Hz).
So I redid the test with Spectrum III / DELL using the various Mode 5 (sync on green) dip switch settings but none would get me a working image using the Spectrum III. The card itself was set to 1024x768 @ 60Hz. I also tried with 1024x768 @ 75Hz. Neither worked with any of the Mode 5 dip switch settings.
Would a fast, non-inverting buffer help? This isn't crazy speeds is it, its not like pixel clock, its going to be once per line or once per full screen (I wasn't paying enough attention sorry).Hmm...since you have a scope, compare the sync width and shape between the PC-8 and Spectrum/24 III. The rework cap on the Bt output that is bent over the top of the part on Spec/24 III (which I think is on green - but check the pins) is there to minimize vertical line shadowing (voltage ringing/overshoot). The cap doesn't completely eliminate the problem, but it fixes it beyond the threshold of general user awareness/detection. So, maybe the sync is out of spec vs. the Dell monitor requirements, or maybe the cap is affecting the waveform in a way that prevents it from syncing (it's going to round it off and, therefore, shorten the valid high period). The video signal is obviously present and functional based on the other monitor you have, so it must be some spec/voltage issue. Maybe the Dell FP is more sensitive to deviations and requires longer to sync up. The problem might also relate to other aspects of the video timing (blanking, etc.). As a quick test, you could try just removing the cap to see if that changes the behavior, but there will be increased vertical ringing in the video output visible as shadowing on high frequency color changes -- like the black and white borders of folders, etc.
Edit: (...and for that cap, there may be a better way to fix -- or prevent -- the problem. It was just the easiest manufacturing rework hack so that the board could ship. But, it would be a research project. For example, the problem may be lack of VRef stability, etc., or some other instantaneous power draw issue -- which is probably greatest when transitioning from black to white. So, if not specifically an output problem, maybe there is a front-side or local bulk capacitance solution that would work...but require more parts or be trickier to implement -- who knows? It could also just be a Brooktree issue that requires overshoot management. However, I think this issue was addressed more successfully in later boards -- whether Bt or ADV-based -- to improve general video quality.)
Would a fast, non-inverting buffer help? This isn't crazy speeds is it, its not like pixel clock, its going to be once per line or once per full screen (I wasn't paying enough attention sorry).
Edit : So double figure μS speed range minimum if it was once per scanline. Which well within the speed of any buffer you're likely to use.