Superbrain #3 : The Superbrain II board

[1024MAK]

Incidentally, you should see the total lash-up I have on my desk... this'll make you laugh!

Who said you shouldn't muck about with CRTs outside their cases?

Nice lash-up

But I think you are missing a vital item. Where is the cup of tea / soft drink?

Only people scared due to the internet being full of death/doom mongers have a thing about uncased CRT displays... Go back to only ten to fifteen years ago, and most TV shops that carried out repairs would have had many sets running on soak test with most of their cases / covers not fitted

No different to having an internal combustion engine running while not housed in a chassis.

Safe as long as you are not stupid or silly enough to put your bits in harms way

Mark

[PS I may be more than a bit biased, as in my job, a lot of the time we work on live electrical systems].

[leenew]

Any good for you Jon??
https://www.ebay.co.uk/itm/Green-Screen ... ctupt=true

Lee.

[jonb]

Good spot, Lee.. I'll think about it (having just bought a 9" B&W monitor)... If it was white or amber I'd snap it up!

[jonb]

Definitely on my way. Decided the breadboarded sync mixer wasn't cutting it, so did some seriously old school electronics on a bit of blobby board:

Top view, nothing to see here..

But underneath, it looks like a logic board from a 1960s IBM mainframe!

Not sure it works yet.


Edit: No, of course it doesn't.

[jonb]

Hmm, I think I fixed it but it looks like the GT65 has had it for now.

Drat, drat and double drat!

[jonb]

I spoke too soon, obviously.

Not only has the GT65 failed, but the LCD TV behind it just went POP and released some magic smoke.

On the underside, we can see that the tiny surface mount semiconductor, Q801 has completely exploded.

And the big transistor, Q802, is split in half!

Not having much luck today!


It might be worth repairing, if I could find out what Q801 is...

[jonb]

Some better news. I had another fiddle with the GT65 and it is working again.

Deflection is still bad, though, but for some reason I prefer it to the LCD. I also acquired a small 9" monitor from a well known auction site for the princely sum of £17 but it turns out to be not working well at all. A disappointment (thanks to a vague description that implied it worked) but it may be useful for parts. Or, I may get it working again (pigs may fly, too).

[jonb]

Hitachi 9" monitor repair thread: viewtopic.php?f=45&t=16381

Image generated by the SB II: download/file.php?id=43326&mode=view

Image generated by an Atom: download/file.php?id=43331&mode=view

Bearing this in mind, and the similarity between the images generated by the Hitachi and Amstrad GT65 monitors, I think the Superbrain's video signal is off slightly. I think I need a bit of advice on diagnosis. To recap: it provides separate H and V sync, plus luminance and I am using one of MNark's sync mixers plus my own PCW video mixer to generate composite sync. I can get an image on the GT65 if I fiddle about with the B+ power supply but I think that is luck, and the image is too wide. On the Hitachi monitor, prior to the repair, I could see the image albeit squashed to the top of the tube. A consequence of bad vertical deflection.

I could swap out the CRTC or other ICs that interact with the sync pulses.

I did notice one other thing. If I disconnect H or V or both sync signals from the mixer board it doesn't seem to affect the signal.

I can apply my scope to the H and V sync signals, but what should I look for?

[1024MAK]

At this link there is details of what a 625 line, 15625Hz, 50Hz (in other words, a PAL) video signal should be like. Complete with timing information.

Mark

[jonb]

OK. I've double checked the sync mixer and it looks OK.

Here is a scope trace. CSYNC is the mixer output and HSYNC / VSYNC are the inputs.

Y=CSYNC, C=HSYNC, B=VSYNC

Zooming into the VSYNC:

Y=CSYNC, C=HSYNC, B=VSYNC

Question - should the HSYNC pulses still be present in CSYNC while VSYNC is low?

[jonb]

More traces..

Y=Composite Video, C=HSYNC, B=VSYNC

The composite video signal doesn't look much like the one on http://martin.hinner.info/vga/pal.html

Let's zoom in..

Y=Composite Video, C=HSYNC, B=VSYNC

This is the start of a line. I'm a bit surprised that the pixels are not proper square waves but they do result in some display (which can be correctly resolved by the LCD monitor). I cannot see a back porch:

Y=Composite Video, C=HSYNC, B=VSYNC

..although the line duration looks to be correct (64uS according to the info site).

[jonb]

Ah...

After some adjustment (of the video mixer trimmer and H-HOLD) I seem to have a picture. Deflection is still way out though (too wide, too tall). Let's see what adjustments this monitor can make. Probably not enough, like the GT65 - I think the Superbrain's video output is to blame.

[jonb]

This is about as good as it gets. In order to shrink the image I had to adjust the B+ voltage (should be 12v, probably nothing like that now) as it has the side effect of zooming the picture (and changing the brightness). I've also adjusted V-height and Linearity, and H-width as far as it will go. Despite the picture, the image is not particularly bright or clear. upping the contrast or brightness results in blooming that blurs the image (and there is no focus adjustment).

[jonb]

Another minor update.

In order to get access to the SB II's serial ports, it's necessary to build a stand in for the "Intermediate Board", which is a small daughter card that provides the main and aux serial ports, as well as a place to mount the SB II CRT's brightness control. It connects to the 50 way IDC plug at the top of the main board (JP1), so I had to fish out the proper connectors. I built the thing out of prototyping board and point to point wiring and used an ATX DB9 connector. Only the Main port is implemented at the moment. After the usual faffing about with null modem adaptors and the like (not needed here as it turned out) and grounding the /RTS line on the main USART, I was able to use a USB-Serial adaptor to transfer files to/from my PC with Kermit.

So now the "lash up" looks quite a bit better:

Next steps will be to build a case for it in plywood, then see if the GT65 parts can be made to show a better image. I'll probably do the case in two parts; a base to hold the boards and PSU with a removable shelf for the monitor and HxC to sit on; then once I find a 12" monitor or get the GT65 working I'll build out the top part of the case that actually encloses it. I'm planning on making it look like a real Superbrain II (that is probably a bit too ambitious!) and I'll be on the lookout for a pair of full height floppy drives as well. I've got some BBC 1/2 height drives but they're only single sided so will not be able to read the QD spec floppies.

I have to say, this SB II main board project has been tremendous fun so far!

[jonb]

GT65 is kind of working now, thanks to some very helpful guys over at CPCWiki.

To reduce the width, it turned out that a reduction in one of the high voltage capacitors feeding the LOPT was necessary (wise? We will see!). Full details, if you're interested, here: http://www.cpcwiki.eu/forum/amstrad-cpc ... djustment/.

So now I can proceed to the "woodworking" phase, because of course it needs a nice box to sit in.

[mister35mm]

I have always wanted a Superbrain, or something similar.

[jonb]

There is nothing similar. It's my favourite CP/M machine.

But you might consider:

• A TRS-80 Model II (with 8" floppy drive) and Lifeboat, Aton or Pickes & Trout CP/M (I have one)
• A TRS-80 Model IV with CP/M
• A TRS-80 Model IVP (portable), again with CP/M
• Northstar Advantage
• Kaypro 2 (but has 9" screen)
• Philips P2000C (this has a built in SASI interface) (also 9" screen) (I have one)

The problem is they are quite rare and thus, valuable - to the right buyer.

All of these machines are supported by cheap-ish IDE implementations of one sort or another. For instance, I've just finished implementing uIDE drivers for the Superbrain. You can boot and run the whole thing without accessing the floppy drives. (uIDE is my own universal IDE interface for Z80 machines).

But if you really want a cheap CP/M fix, go for an Amstrad PCW. Or even better, build one yourself in a cheap FPGA board : http://searle.hostei.com/grant/Multicom ... gaCPM.html

Then make it go like hot snot off a shovel: https://www.retrobrewcomputers.org/doku ... jonb:start

CP/M at 50Mhz!! Whoosh!

Then make it look cool: viewtopic.php?f=41&t=12954&p=222030#p221457

[jonb]

So, after acquiring a lovely little amber monitor from a well known auction site for not much money, we have this:

Close up.

Mmmm lovely amber goodness...

I think there are still some adjustments needed (especially to the focus) but overall I'm pretty chuffed. I could probably do the uIDE drivers for it now (if I wasn't busy with the uRTC project)..

[SteveH]

You teasing us all Jon? What's this about a uRTC project?

[jonb]

Hi Steve

uRTC - Universal RTC for Z80 computers.

Fits onto the Z80 bus used by uIDE and attaches as shown using stand offs.

Like uIDE it is programmable for the base I/O address, but the RTC chip needs 8 of them as it has 8 registers. I am using the Superbrain 1 to develop the utility suite as my Amstrad PCW serial interface has packed in so I cannot transfer test code to it. There is a discussion over on the CPCWiki forums if you're interested : http://www.cpcwiki.eu/forum/nc100-nc200 ... ad-pcw-rtc.

(The machine featured in this thread is a Superbrain II which already has a battery backed RTC on-board.)