Superbrain QD Nearly Fixed?

[alan8086]

Hi all,

Just a quick vid and rundown of where I'm at with my 12 year Superbrain quest:

A pick of the Mboard after all the socketing etc I've done:



I've socketed about 15 of the glue logic chips - partly to test them on my ABI Chip tester and partly just so I could see where traces go.

I replaced the PPI chip socket - previously when pressure was applied to that chip, it would cause distortion or a 'change' on the display. This was an intermittent connection where a trace met a through hole pad, now repaired and a new socket in place.

The CRTC chip socket has similarly been replaced, another bad contact beneath it. Z46 and Z48 were socketed so I could see where traces went and check continuity back to the CRTC chip.

The VDAC socket has been replaced - it was crusty with bits of IC pin stuck in one of its sockets.

The EPROM socket has been replaced - again, its been de socketed so many times, thought it deserverd a new turned pin socket.

The only non glue logic original sockets left are the 2 CPU sockets and the FDC socket.

The above is mainly for JonB who is kindly acting as my SB consultant!

Any other comments are welcome regarding a way forward. Personally I do think trying a replacement CRT8002-003 VDAC chip is worth a go. I have 5 of them, so it seemed unlikely that ALL of them have failed, but if I leave that socket bare, with no chip, the SB behaves in exactly the same way. Of course that may just mean there is an issue in the circuitry before the VDAC? Most of the IC removal/testing has been centred on ICs relating to the VDAC chip thus far.

Anyone have a CRT8002-003 chip for sale? The 003 bit is important and I've not seen that variant online so far.

Thanks,

Alan

 

[JonB]

Hi Alan

As I said in my PM, you are nearly there.

The following is for the interest of the readers (as I have said all this via PM already).

That machine is definitely booting up. The seek noises are typical: tick - delay - tick tick and the keyboard response and beep indicate that the BIOS is loaded and running. The positioning of the block cursor is consistent with a successful boot.

I think it is strange that all of your spare CRT8002s are damaged. One of them must be OK. Problem is, until you test them on a known good SB you won't know. At a pinch, you can use a CRT8002 (no suffix) to prove that everything else is OK, but you won't see properly formed characters (they will be readable but the right hand side of each character will be truncated). I have one of these that I could lend you. Or you could send me your 8002s and I can test them in my SB. I think the sooner we eliminate this chip as a source of the problem, the better.

 

[alan8086]

Hi Jon,

Thankyou again for more input - I will get 4 CRT8002's and your cleaning disks packaged up tonight!

I sound like an obsessed oddity but I keep picturing how it will feel when I finally see that 'Insert disk' prompt! I had a real mania for these machines as a kid, that was around 1989/90. In 2007 I decided to revisit my mania and got a free/non working SB off eBay and 12 years on - nearly there!

Also need to Kryoflux the disks I have for it as the intriguing thing about this Superbrain is the Micronix PixelPlotter board it has. I assume the disk labelled 'graphics progs' is for that device. I've tried ImageDisking it after a clean with alcohol, I got a few good sectors and then a load of unreadable ones. Oh well, next project!

Hi Alan

As I said in my PM, you are nearly there.

The following is for the interest of the readers (as I have said all this via PM already).

That machine is definitely booting up. The seek noises are typical: tick - delay - tick tick and the keyboard response and beep indicate that the BIOS is loaded and running. The positioning of the block cursor is consistent with a successful boot.

I think it is strange that all of your spare CRT8002s are damaged. One of them must be OK. Problem is, until you test them on a known good SB you won't know. At a pinch, you can use a CRT8002 (no suffix) to prove that everything else is OK, but you won't see properly formed characters (they will be readable but the right hand side of each character will be truncated). I have one of these that I could lend you. Or you could send me your 8002s and I can test them in my SB. I think the sooner we eliminate this chip as a source of the problem, the better.

 

[JonB]

I had a real mania for these machines as a kid, that was around 1989/90.

A comment made about classic sports cars: Never drive your dream car.

Fortunately the SB is a bit more predictable - it's a competent CP/M computer with a smaller than average TPA, much like any other CP/M box of the time.

Where it scores is:-

• Looks pretty cool
• All in one single unit
• Has a clear screen and a really nice keyboard
• You can fit uIDE to it for hard disk goodness - and it boots too, so your disks and drives can have a rest

Don't forget to implement the motor_on mod so the drives shutdown when not in use. Other useful improvements I've done include fitting an auxiliary 12v PSU to drive the floppy motors (prevents the screen wobbling) and a modern 12v quiet fan (with some resistors inline to slow it down, so the machine is nearly silent now). I also built a new cable to go between the PSU/Serial board and the main board as my original ribbon gave up after too many disconnect / reconnect cycles.

 

[StephenM]

Hi Alan, I had a problem with inverse video and it came down to me accidentally cutting a leg on the 74LS86N.



Possible trace break or faulty logic?

 

[alan8086]

Hi Alan, I had a problem with inverse video and it came down to me accidentally cutting a leg on the 74LS86N.

View attachment 53893

Possible trace break or faulty logic?

If those are the 06 and 86 next to the VDAC IC, I have them both socketed and with tested good ICs. I've traced back to where the pins should go to using the schematic and continuity test too - cant see any issues within my limited technical competence anyhow!

I have a CRT8002 on its way from Russia - Hopefully I wont have to wait the full 3 - 4 weeks for its arrival!

BYW - what software do you have for your SB and what do you 'do' with your machine?

Thanks for your reply

 

[alan8086]

A comment made about classic sports cars: Never drive your dream car.

Fortunately the SB is a bit more predictable - it's a competent CP/M computer with a smaller than average TPA, much like any other CP/M box of the time.

Where it scores is:-

• Looks pretty cool
• All in one single unit
• Has a clear screen and a really nice keyboard
• You can fit uIDE to it for hard disk goodness - and it boots too, so your disks and drives can have a rest

Don't forget to implement the motor_on mod so the drives shutdown when not in use. Other useful improvements I've done include fitting an auxiliary 12v PSU to drive the floppy motors (prevents the screen wobbling) and a modern 12v quiet fan (with some resistors inline to slow it down, so the machine is nearly silent now). I also built a new cable to go between the PSU/Serial board and the main board as my original ribbon gave up after too many disconnect / reconnect cycles.

Hi Jon - I'm in agreement with all that! Out of the 4 lumps of vintage tech I have, the SB seems the most 'convenient' and practical to use. An early All in One PC! My IMS 8000 is a heavy lump which requires a laptop, hyperterminal etc. The NEC APC is just as heavy though has a built in colour screen but not a great deal of available software. My Compaq Portable III - I just don't use much!

Oh, I got as far as finding a box, placing 3 cleaning disks within, packing 3 VDAC and 4 VDUC ICs in IC tubes and no further!

I've started de soldering non working keys off the motherboard and cleaning the gold contacts inside. The mechanism surprisingly robust and simple. - not much to break and finding gold in anything is usually a sign of quality - back then anyhow!

 

[JonB]

You need to take a trip to the Post Office. Come on, you can do it!

The keys are the same as those used in a BBC Master, so if you struggle with any of them replacements are reasonably easy to get hold of.

SMK Type 4 Linear: https://stardot.org.uk/forums/viewtopic.php?f=9&t=12890&p=166220

Having said that, I needed a new one because the stem was broken and all attempts to glue it together failed. Otherwise, cleaning them gave good results.

Regarding your Russian 8002. Is it -003 or no suffix variant?

Regarding software and usage, I have pretty well all the main CP/M software installed on a uIDE board, but I don't use the SB for anything in particular (other than to develop the uIDE BIOS). It just sits around looking pretty. The next time I use it will be for uRTC development (a real time clock to connect to the uIDE bus cable). When I finally get the boards from China, that is..

 

[alan8086]

I'll try again with a courier this weekend - I have nothing but disdain for the PO.

There is a key with a broken stem on my SB MB - the one I am fixing up is defiantly the most scrappy of the two, in terms of broken traces, keys and general battered-nes I'm just aiming for functionality ATM though.

My CRT8002 has no suffix. It was the cheapest I could find, about £9.80 including postage. According to tracking, its coming from Wuhan in China. despite the cyrillic characters I saw at one point.

The only suffixed 8002 I can see on eBay is a -025 which doesn't get mentioned on the datasheet. Looking at those character encoding graphics, the -018 seems similar to the -003 so is that another one to look out for?

Barring that, I was thinking of inventing the thing that allows the External mode on the crt8002 so I can have a board with a 2816 EEPROM with the correct encoding, and maybe others for other languages etc? I will have to do some more research however once my brain works.

How hard would it be to 'invent' the impossibly rare S100 adapter card for the SB? Using the External IO bus that comes from the Z80? I had one years ago - dont remember there being that may ICs on it? If i went to the bottom of a certain hill in Cheshire, with a metal detector, I'd probably find it again!

 

[JonB]

Ah yes, the dreaded hill. A tragedy!

The 8002 will work but as I said before it will give you chopped off characters. You can still use the computer with it.

So, for the S100 board it is a matter of matching the signals coming out of the expansion port with the S100 bus signals present on a Z80 S100 machine (one of which I believe you have). As the S100 is a passive bus, you shouldn't need anything other than a point to point. Do bear in mind, though, that S100 boards require power supplies that are out of range of what the SB supply offers (8v / 16v unregulated) so you'd need to fit a separate PSU. I'm not sure how the Intertec adapter overcame this, but I do know the expansion port doesn't have every Z80 signal on it. It has 0v, +5v, D0-D7, A0-A15 and the following control signals: /RST, /INT followed by I/O signals /IN, /OUT (these are pre-combined with /IOREQ) and /RD, /RW (pre-combined with /MREQ). We don't get /IOREQ, /MREQ, /M1, /WAIT, /BUSREQ, /BUSACK, /REFSH and one or two others I probably missed, so recreating a genuine S100 bus with all Z80 lines is not possible. Thus, it will limit compatibility (quite greatly, I imagine). You might try to get the signals direct from the Z80 with a shim as I do for uIDE. So a Z80 - S100 bus adapter could be built, subject to further investigation.

Next, the question becomes "what additional functionality do you want to add via S100?"

If it's mass storage you want, I have that covered.

Incidentally, the Intertec schematic pack I have here (genuine printed document) has a diagram for the Intertec Hard Disk adapter but not the S100 adapter, sadly.

 

[alan8086]

Another bit of progress...



Picture is dim because it's between the 50hz/camera shutter speed

Now I can type accasional correct characters but usually just get ??????? When a key is pressed. The DIR listing is a one off until I fix ths issue.

 

[JonB]

OK, this is good. Next up we need to fix the ??? issue. It could be one of a number of different problems but from the sound of what you've written via PM it could be one of those bad connections.