Superbrain #3 : The Superbrain II board

classic non-acorn hardware, software & languages
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1024MAK
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Re: Superbrain #3 : The Superbrain II board

Post by 1024MAK »

If the semiconductor devices that are attached to the heatsinks don’t get too hot, consider fitting insulation kits to them. I prefer the thermal pads (e.g. silicone type pads), don’t forget the plastic bush for the machine screw/bolt.

Mark
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jonb
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Re: Superbrain #3 : The Superbrain II board

Post by jonb »

Hi Mark

I did consider that but the TIP110 bolted to the heatsink does get quite hot, so I insulated the rear of the chassis instead (with a 3D printed cover).

I have a little more troubleshooting to do on the one servo board, then I can move on at last.
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Witchy
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Re: Superbrain #3 : The Superbrain II board

Post by Witchy »

Drive wise I'm the same, 2 workers in the SBII and none in the SB1, but since that's booting from Gotek it's less important and can wait until I've got nothing better to do. Trouble is, with this collection there's ALWAYS something to do.
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jonb
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Re: Superbrain #3 : The Superbrain II board

Post by jonb »

As I'm going to be messing around with the drives in the SB I I thought it'd be a good idea to print another shield...


SB Drive Bay shield.jpg


Although the slot isn't quite positioned correctly, it is only 2 layers so very easy to trim with a pair of scissors.

And now we come to the interesting part. Using the Gotek as A: and the B: drive I am having difficulties with on the SB I with the floppy cable from the SB II as well, I see no problems formatting or copying data to the B: drive. So I am forced to conclude that something is wrong with the interface on the SB II. This is good news in that it means my TM100s are probably OK, but not so great if it means the SB II floppy interface is playing up.
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jonb
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Re: Superbrain #3 : The Superbrain II board

Post by jonb »

Quick update.

2xTIP110s arrived, soldered in and drives running again. New SCR arrived, soldered into the PSU and that is working too.

Adapter boards arrived but the uIDE port is wired wrong. Fixed that with some patching on the PCB, but I am getting dropped bytes on the read operation. It's probably because the timing on the IDE board is so tight. I had to use expansion port signals only, which means /IN and /OUT which are combined /read and /ioreq plus /write and /ioreq. I wonder if the additional gate on the /in line is causing the problem. Anyway, I've sort of given up on that and will just use the board as the adapter between SB II main board and SB I PSU, for the time being. I'm just verifying it is all connected properly before plugging in the SB II main board. I got the floppy power connectors wrong way round too. Darn it! But I can turn the connectors round to remedy that. Don't want any more magic smoke!
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jonb
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Re: Superbrain #3 : The Superbrain II board

Post by jonb »

Fitted the adapter board last night, after spending a long, long time trying to get the uIDE port on it working.

IMG_7353.jpg

The adapter is the purple board to the left of the fan. It's providing the connection between the PSU board (main / aux serial ports, video signals and power) and the SB II main board. It has additional power sockets for the fan and Gotek (that's the 3.5" power plug), and could provide power to the main board but as I already have this connected via a loom to the screw terminals on the PSU I will leave that as-is. The Tandon drive (B:) is also going to be connected to the screw terminals as it has the (relatively) high current 12v motor.

So far, in testing, it checks out fine apart from the uIDE port. No magic smoke, hooray! I've refitted a shim to the CPU1 socket on the main board and that is how the uIDE will be connected. Life's too short... :)

Now I am going to return to debugging the Tandon drives, and longer term a respray is on the cards for the case. When I can find a good enough paint match!
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Re: Superbrain #3 : The Superbrain II board

Post by jonb »

I’m still left with a non working B: drive. A: is fine, and this is why I hadn’t considered the SB II’s drive circuitry. But eventually it dawned on me that, if the B: drive from the SB I worked fine in the SB I, but not in the SB II, it must be the SB II’s board. Oh dear.

I had a look at the schematic pack. On both machines is a re-triggerable one shot (called Z75 on the SB I) – a 74LS123 – and it is used to condition the read pulses coming from the floppy disk. Someone had hand annotated a resistor change in the one shot’s timing circuit – it said 5.6k and “from 150ms to 200ms”. The resistor is 4.7k on the printed schematic, but my board has a 5.6k. I thought I’d try a 4.7k resistor, and I got better results (still not perfect). But the circuit also has a capacitor, 56pF, so I replaced that too, and this seems to have done the trick, although I am stuck with the ratty drive as B: since the nice drive is misaligned (and I couldn’t correct it).

Finally, I was ready to reassemble the case. I spent most of today fiddling about, trying to get the keys to line up with the bezel, and drilling new holes for the PCB mounting screws. Some lining up of the drive / CRT chassis, and a pair of spacers on the CRT mounts, and it is looking much better. Finish off with a wipe of Armor-all low gloss silicon spray and it looks much tidier. Still needs a respray but it’s bearable for now.


Superbrain II QD with uIDE and Gotek. If only someone hadn’t tried to rub the paint off, it’d be bearable. I now need to respray it and restore the label below the drives.
Superbrain II QD with uIDE and Gotek. If only someone hadn’t tried to rub the paint off, it’d be bearable. I now need to respray it and restore the label below the drives.


I checked the first post on this thread and discovered that this particular voyage of retrocomputing goodness has taken over two years (I received the SB II board early January 2019). Gosh, that is a long time to wait for a repair... but I have stuff that's been waiting longer... don't we all?


Until next time!
JonB
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