WarpSE: 25 MHz 68HC000-based accelerator for Mac SE

[Zane Kaminski]

Just to reiterate, here is a scope trace showing the probable reason that the monitor won’t sync correctly:

When the HSYNC signal is low, the beam of the CRT is drawn to the left of the screen so as to start scanning out a new line left-to-right. To an LCD’s controller or the DVI gizmo we have been discussing, the HSYNC low pulse is a hint that the the next video line is starting soon.

Issue here is that HSYNC stays low for way too long such that the HSYNC low pulse overlaps with the first 1/4 of the active video portion. So I’ll apply the high-pass RC filter as on the Power-R gizmo to limit the HSYNC low pulse width. Then hopefully one of my monitors will sync despite the 22.25 kHz HSYNC frequency (corresponding to the 342p resolution) being lower than the specified minimum of even the best multisync displays like the NEC LCD1860NX and HP L2335. They all officially only work with a > 30 kHz line rate corresponding to 480p or higher. They do sync to LCs at 512x384 though which have a similarly low like rate of 24.48 kHz. So with luck, the HSYNC pulse limit circuit will work with the monitor and we can proceed with the WarpSE debugging.

 

[alxlab]

Oh that picture of the SE video signal is gold! Yeah it's exactly what has been mentioned but never see a picture.

Just to be clear for people, here's what normal VGA hsync with video signal should look like.

 

[alxlab]

Just curious but on your power board I noticed you use two XOR chips and separate the RGB signals VS just connect the RGB pins all together like on t http://www.waveguide.se/?article=compact-mac-video-adapter

I was wondering what the logic behind the design is?

 

[retr01]

So take the low voltage RGB signal, over-sample, then produce the right VGA HSYNC at a higher voltage so that the modern display can understand and process to the screen? Can the Pico detect the RGB signal that low?

There is no VSYNC from the compact Mac's video chip, correct?

 

[Zane Kaminski]

Just curious but on your power board I noticed you use two XOR chips and separate the RGB signals VS just connect the RGB pins all together like on t http://www.waveguide.se/?article=compact-mac-video-adapter

I was wondering what the logic behind the design is?

Well the XOR gate is just so that I can choose whether to invert the hsync/vsync/video signals with a jumper.

As for why they're separate, it's a transmission line effect thing. I wanted to use a both-ends termination where there is a 75 ohm termination resistor not just at the load (monitor) but also at the source (adapter gizmo). Why? It makes it work better with a crappy VGA cable. You can get signal reflections with bad VGA cables where things on screen have a "ghost" image some distance to the right proportional to the cable length. Double the cable length and the ghost image moves 2x further to the right. It's from impedance discontinuities--bumps in the road so to speak--sort of causing a reverse echo to be sent backwards down the line back toward the video source. Without a proper termination there to attenuate the signal reflection, it bounces back toward the monitor, creating the ghost image some time later.

You can see this effect in a swimming pool at the boundary between the shallow end and the deep end. Make big wave with your hands in the shallow end going toward the deep end. When the wave crosses the line between the shallow and deep ends of the pool, it will reduce slightly in height and a little negative wave will be sent backwards toward you. In the monitor cable, the depth of the pool is like the cable impedance. If the impedance of the cable is far from 75 ohms or there is an impedance discontinuity--a spot where the regular geometry of the cable is disturbed like a connector--this will create a reflection like the one created when the wave crosses into the deep end. Water has a lot of attenuation so the reflected wave does not last for long, but you could conceive of it splashing against the back wall of the shallow end and going again toward the deep end. This is what creates the ghosted window effect. With the 75 ohm source, when any reflections hit the VGA adapter, they are attenuated as if the shallow end was infinitely long and there was no back wall for the wave to bounce off.

VGA video is 75 ohm impedance so in order to add the termination to the output of the adapter, I had to use a resistor network to take the 3.3V signal from the 74LVC gate and turn it into a 1.4V signal with 75 ohm output impedance for each line. This will get cut in half to 0.7V when plugged in to the 75 ohm terminated monitor.

I could use a single 74LVC gate and connect them all together but then uhh, the combination of three 75-ohm transmission lines in parallel would be like 25 ohms. So to match the impedance correctly with all three lines paralleled, the output impedance of the gate oughta be 25 ohms. For 74LVC series, the output impedance is pretty poorly controlled, like 10-30 ohms. It's hard to make an accurate resistor on a chip. So ratiometrically compared to the desired 25 ohm output impedance, you could have on the order of 2.5x too low impedance or 20% too high, making it a poor attempt at the both-ends termination and it won't have as good of an effect on the signal. You could add a 5 ohm resistor to get 15-35 ohms to sort of center the inaccuracy around the desired 25 ohms but realistically you can't make it any better with such a low impedance. So instead I used three separate gates for each of R/G/B. That way the target impedance would be 75 ohms and the 10-30 ohm range is smaller in comparison, making the termination work better.

 

[Zane Kaminski]

Garrett just finished the rest of the assembly of some WarpSE prototypes:

I’ve gotta redo the clock switching and DIP switch logic as I mentioned a while ago, then I can try it out!!!!

 

[Zane Kaminski]

Garrett just fixed the video gizmo with a new bodge circuit:

And now the video is working on the multisync LCD:

Sort of. Guess this Mac SE board is messed up. Gotta fix that and then we can continue.


Edit: That was easy. Just had to jiggle the SIMMs a bit.

 

[retr01]

LOL! My SE/30 screen got crazy. Fix the memory, all good.

It makes me wonder how many have gone too far troubleshooting and missed the RAM?

Cheers!

 

[alxlab]

Did heat cause this?

 

[Zane Kaminski]

Did heat cause this?

View attachment 6245

Sort of. That's the result of being in 85 degC Simple Green solution for an hour. The reason for this was that we couldn't find our preferred cleaning agent, Zep Industrial Purple Degreaser. So we tried Simple Green, ostensibly a similar product. Most important thing about the choice of cleaning agent is how quickly it damages the board (as shown) compared to how quickly it removes flux and other gunk. An hour in hot Simple Green caused this result and it didn't even remove the flux residues, even with intermittent ultrasonic during the hour (maybe 10 minutes total). An hour in Zep would have been much worse for the board but it only takes a minute or less for 85 degC Zep solution + ultrasonic to remove the flux. So SG fails and we're back to Zep for cleaning purposes.

 

[retr01]

Simple Green caused this result and it didn't even remove the flux residues...only takes a minute or less for 85 degC Zep solution + ultrasonic to remove the flux.

So flux is hard to remove unless there is the right solution and process. 99% IPA is not one size fits all, after all?

 

[Zane Kaminski]

99% IPA is not one size fits all, after all?

Yes, many times over. It often doesn't really wash the flux off, just sort of pushes it around the board. Plus it's expensive compared to water and degreaser. Also don't use 99% (i.e. anhydrous) isopropanol to clean a MacBook keyboard. It wicks up the sides of the keys and weakens the plastic clips underneath. Then a bunch of the keycaps fall off when you blow dry it clean. 70% or 91% is much better for that purpose. Learned that the hard way on my 2021 14" Pro. I thought I was being good to it by using something without water... My old 2015 must have had sturdier or more resilient plastic for the key clips since that never happened on my old machine.

 

[retr01]

Good to know! What about WD-40 or solvalene as a degreaser?

 

[Zane Kaminski]

Good to know! What about WD-40 or solvalene as a degreaser?

WD-40 is a bit too lube-y. Solvalene sounds interesting! I had never heard of it. Contrary to the "-lene" suffix it's water-based. But Zep is fine, just make sure to get it pretty hot in the ultrasonic or else the cleaning action is slow and it screws up the board by the time it’s clean. At 85 degC a light-to-moderate amount of flux comes off in less than a minute and no board damage is done.

 

[retr01]

Solvalene sounds interesting! I had never heard of it.

Here is an example:

Highest Strength Industrial Degreaser | Superior Industries, Inc.

The highest strength and most effective water based degreaser. Removes grease, oils, inks, soot & stains from production equipment, concrete floors, construction vehicles and when diluted properly is the most cost effective product available.

www.superior-industries.com

 

[JDW]

Yes, many times over. It often doesn't really wash the flux off, just sort of pushes it around the board. Plus it's expensive compared to water and degreaser. Also don't use 99% (i.e. anhydrous) isopropanol to clean a MacBook keyboard. It wicks up the sides of the keys and weakens the plastic clips underneath. Then a bunch of the keycaps fall off when you blow dry it clean. 70% or 91% is much better for that purpose. Learned that the hard way on my 2021 14" Pro. I thought I was being good to it by using something without water... My old 2015 must have had sturdier or more resilient plastic for the key clips since that never happened on my old machine.

Thankfully 100% (not that weak 99% stuff ) IPA did wonders to get flux off my SE Reloaded board. As you can see here, I used a toothbrush and soaked it for a half hour. Plastic parts seemed to have come through just fine. I was a tad worried about the electrolytic capacitors (you don't want to get that inside them), but my power-on test shows the board works fine, so they are no worse for wear.

 

[retr01]

100% IPA?! Like this one?

https://amzn.to/3utmiPI

Thankfully 100% (not that weak 99% stuff ) IPA did wonders to get flux off my SE Reloaded board.

 

[alxlab]

And now the video is working on the multisync LCD:

View attachment 6243

Forgot to ask what's the model of the LCD monitor? Sounds like it would be a useful monitor to have around.

 

[Zane Kaminski]

Forgot to ask what's the model of the LCD monitor? Sounds like it would be a useful monitor to have around.

It’s the HP L2335. 1920x1200 resolution. I like it a lot not just because our lab is HP themed but also because it’s an alright display. I believe it has the same panel as the old 23” Apple Cinema Display. These two were the first IPS displays to come to market. Nowadays there are screens with better viewing angles but it’s nevertheless acceptable to put Windows up on and it syncs to basically anything.

 

[JDW]

100% IPA?! Like this one?

https://amzn.to/3utmiPI

I normally use this 100% (not 99.9%) version sold on Amazon Japan:

Amazon.co.jp: 100% Isopropyl Alcohol 500ml IPA 2-Propanol : Industrial & Scientific

Amazon.co.jp: 100% Isopropyl Alcohol 500ml IPA 2-Propanol : Industrial & Scientific

www.amazon.co.jp

But for the bathroom dunking shown in my Part III video, I did use this 99.9% stuff:

https://www.amazon.co.jp/-/en/gp/product/B0B1M8SK8N/

No, there's no noticeable difference once you get past 99%. Just don't use the 70% rubbing alcohol because that has a fair amount of water in it.

In the past, I used Anhydrous Ethanol, but it tended to leave a film, so I switched to IPA.

I'm not sure if this discussion helps Zane, or not, but I just wanted to clarify.

Zane, your work on this accelerator is amazing. If it works without distorting the sound, you will have done better than Levco SuperMac! Honestly, I don't know how they released a product with distorted sound though. I can't remember if there was customer outcry over that back in the day. I do know that @Kay K.M.Mods is not a happy camper about the distorted sound when using his Carerra040 on his SE/30. A big part of the Mac experience is sound, so it's important to get that part right, in my opinion.