Superbrain #1 : The ratty one

Talk about non-Acorn classic computers/hardware/software here (including retro consoles)
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jonb
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Re: Superbrain #1 : The ratty one

Post by jonb » Thu Aug 30, 2018 5:07 pm

Swapped out the 2114 and things are looking better:

Code: Select all

Z80 ICE V0.72 Jun 21, 2011 R. Grieb/Tauntek

OK ===> l 0
0000 3A 00 88       LD A,(8800)
0003 FE 55          CP 55
0005 C2 13 00       JP NZ,0013
0008 3A 01 88       LD A,(8801)
000B FE AA          CP AA
000D C2 13 00       JP NZ,0013
0010 C3 21 00       JP 0021
0013 21 00 04       LD HL,0400
0016 11 00 C0       LD DE,C000
0019 01 00 04       LD BC,0400
001C ED B0          LDIR
001E C3 06 C0       JP C006
0021 31 FF 8B       LD SP,8BFF
0024 3E 00          LD A,00
0026 32 00 88       LD (8800),A
0029 32 01 88       LD (8801),A
002C 32 07 88       LD (8807),A
002F 32 06 88       LD (8806),A
0032 D3 10          OUT (10),A

OK ===> d 480

0480   23 C3 77 C0 33 2E 31 20-20 20 49 4E 53 45 52 54    #.w.3.1   INSERT
0490   20 44 49 53 4B 45 54 54-45 20 49 4E 54 4F 20 44     DISKETTE INTO D
04A0   52 49 56 45 20 C1 01 00-FF CD 71 C2 CD B6 C2 CD    RIVE .....q.....
04B0   AA C2 E6 80 CA CB C0 CD-70 C0 01 00 00 CD 71 C2    ........p.....q.
04C0   CD B6 C2 CD AA C2 E6 80-C2 BA C0 21 80 C7 11 01    ...........!....
04D0   00 01 00 01 CD 60 C2 C3-80 C7 E5 D5 C5 F5 DB 69    .....`.........i
04E0   E6 04 CA F1 C0 CD 25 C1-DB 48 F1 C1 D1 E1 FB ED    ......%..H......
04F0   4D CD 0F C1 C3 E8 C0 E6-7F 47 FE 20 FA 04 C1 78    M........G. ...x

OK ===>

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Re: Superbrain #1 : The ratty one

Post by jonb » Thu Aug 30, 2018 5:13 pm

..much better..
CCH SB rides again.jpg
CCH Superbrain rides again!

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Re: Superbrain #1 : The ratty one

Post by hoglet » Thu Aug 30, 2018 5:15 pm

=D> =D> =D> =D> =D>

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Re: Superbrain #1 : The ratty one

Post by jonb » Thu Aug 30, 2018 5:43 pm

Cheers Dave

Just need to recap the PSU, fit the auxiliary 12v supply and a 12v fan, reassemble it then on to the next challenge.

Gotta say, all that CP/M goodness on my desk brings a warm feeling to my heart!

:D
Last edited by jonb on Thu Aug 30, 2018 5:44 pm, edited 1 time in total.

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Re: Superbrain #1 : The ratty one

Post by 1024MAK » Thu Aug 30, 2018 6:38 pm

jonb wrote:
Thu Aug 30, 2018 5:43 pm
Gotta say, all that CP/M goodness on my desk brings a warm feeling to my heart!
Best fit a heatsink to that ASAP :lol:

Well done Jon =D>

Dare I say it, your getting good at these repairs :D

Mark

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Re: Superbrain #1 : The ratty one

Post by leenew » Thu Aug 30, 2018 7:22 pm

Well done Jon (again!) =D>

Lee

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Re: Superbrain #1 : The ratty one

Post by jonb » Fri Aug 31, 2018 8:00 am

Hmm, well I gave up on alan8088's mainboard and returned it. Not my finest endeavour. Now, for this CCH machine I need to recap its PSU, fit the auxiliary 12v supply (Meanwell, not some off brand Chinese junk!), replace the dead 115v fan with a 12v fan, refit the floppies (and fix Drive B: which was broken). Still a way to go, but it is all easy peasy apart from the broken drive which needs investigation.

Meanwhile, thanks for the moral support and advice. What a great forum! :D

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Re: Superbrain #1 : The ratty one

Post by jonb » Fri Aug 31, 2018 8:01 am

1024MAK wrote:
Thu Aug 30, 2018 6:38 pm
Dare I say it, your getting good at these repairs :D
Mark
The praise of the praiseworthy is above all rewards.

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Re: Superbrain #1 : The ratty one

Post by leenew » Fri Aug 31, 2018 8:29 am

jonb wrote:
Fri Aug 31, 2018 8:01 am
1024MAK wrote:
Thu Aug 30, 2018 6:38 pm
Dare I say it, your getting good at these repairs :D
Mark
The praise of the praiseworthy is above all rewards.
Hmmm..... I wonder what MY praise is worth? :-k :lol:

Lee.

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Re: Superbrain #1 : The ratty one

Post by jonb » Fri Aug 31, 2018 8:50 am

Lee, thanks for that, I actually laughed out loud!

:D

Thank you, too, for your kind words. I think we're in the same boat - as "journeymen", learning how to fix retro computers. For my part I find that my path to success is helped greatly by people like Mark and Dave, who are experts and (more importantly from my perspective) are willing to share their expertise and time to help others. I have been, and always will be, very grateful to them and other people like them. In turn, I hope to be able to contribute myself, one day, in a likewise manner.

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Re: Superbrain #1 : The ratty one

Post by leenew » Fri Aug 31, 2018 8:55 am

jonb wrote:
Fri Aug 31, 2018 8:50 am
Lee, thanks for that, I actually laughed out loud!

:D
Glad I could be of assistance in *some* way then :D
jonb wrote:
Fri Aug 31, 2018 8:50 am
Thank you, too, for your kind words. I think we're in the same boat - as "journeymen", learning how to fix retro computers. For my part I find that my path to success is helped greatly by people like Mark and Dave, who are experts and (more importantly from my perspective) are willing to share their expertise and time to help others. I have been, and always will be, very grateful to them and other people like them. In turn, I hope to be able to contribute myself, one day, in a likewise manner.
You are of course correct. The time that some experts are willing to give, and the patience that they show to members of all levels of abilty is quite incredible =D> =D> =D>

Lee.

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Re: Superbrain #1 : The ratty one

Post by 1024MAK » Fri Aug 31, 2018 9:50 am

Ah, now, let's not get carried away. I don't consider myself to be an expert. True I do have a couple of qualifications to my name due to attending a technical college back in the 1980's (gosh that sounds so old now :shock:).

But most of my knowledge about fault finding microprocessor systems comes from a combination of my existing electronics knowledge and experience, experience at my job (although 99% is not component level, but 'replace the card' type work), doing my own repairs and modifications on my own systems, and learning from others on forums like this one.

Mark

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Re: Superbrain #1 : The ratty one

Post by 1024MAK » Fri Aug 31, 2018 9:57 am

Oh, and I may occasionally drop the ball (sometimes with magic smoke and smell, sometimes in a big way). But those stories are for another time and place... :lol:

Don't be afraid of going wrong. Learn from it :wink:
And never give up hope, there may be symptoms of multiple faults. Tackle them one at a time :D It's actually rare that a system cannot be repaired after a 'normal'* failure, as long as replacement parts are still available.

* not including extensive damage like a large overvoltage, or lots of corrosion.

Mark

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Re: Superbrain #1 : The ratty one

Post by jonb » Fri Aug 31, 2018 2:39 pm

Which is why I am trying to encourage alan8088 to return the board or his other broken one.

So, back to the CCH machine, I pulled all the elecrolytic caps out of the PSU and ordered replacements. Horrible job, as Intertech liked to bend the legs at 90 degrees to the board prior to soldering and that, combined with the bottom of each cap touching the board, makes them tricky to get out without damaging pads. Looks like I pulled 6 pads and damaged one track this time, not too bad considering what happened when I fixed my own PSU.

Caps out.JPG
Caps oooot!

Most of those pads are not actually connected to anything other than the via they surround. This PSU has none of the old "magic smoke" RIFA caps; instead it's got high voltage plate caps, which I assume are not prone to smoking. I don't know what these are like in failure mode, but my PSU had one that had exploded. However.. I'm not inclined to replace the CCH PSU ones as they look clean with no visible scorch or other marks.

New electrolytic caps on order...
Last edited by jonb on Fri Aug 31, 2018 2:55 pm, edited 2 times in total.

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Re: Superbrain #1 : The ratty one

Post by jonb » Fri Aug 31, 2018 3:18 pm

Oops, looks like I missed one! 10v 47uF..

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Re: Superbrain #1 : The ratty one

Post by jonb » Wed Sep 05, 2018 9:32 am

Some more pictures of the PSU.

I wasn't happy with the way the 240v - 115v step down was wired. One of the wires looks like an earth but it is in fact 115v AC live.

IMG_4900.jpg

On the left hand side of the board, there is an RF filter and fuse. I didn't like the way the wires were coloured, especially the white wire coming in from the mains cable (it was the live), or the green and yellow sleeves on the filter, which were loose and again implying a ground connection.

IMG_4901.jpg

So, I pulled it all out and started again.

IMG_4904.jpg
Rewired! Properly!

The new wiring scheme is:
  • Brown: 240v AC Mains Live
  • White: 115v AC Live to PSU (after filter).
  • Black: 115v AC Neutral to PSU (after filter).
  • Blue: Neutral (shared between 240v mains and 115v as it is common on the step down transformer)
  • Green / Green & Yellow: Earth
I fitted a new mains cable as the old one has illegally coloured wires (White: Live, Black: Neutral, Green: Earth) and also modified the power switch wiring so that it is connected to the 240v incoming (previously it was switching the 115v live, post step down - which meant the transformer was always connected to the mains). No problem here as the switch is a 240v part. All exposed connectors have heat shrink sleeves, apart from the transformer as it's not practical given the "U" shape of the lugs. I may fashion a cover for it, though.

All the PSU caps are fitted, apart from a 10v 4700uF unit that is still in the post.

There is also a Meanwell PSU to wire in to provide a better 12v supply for the floppy drive motors - it's in the post as well.
Last edited by jonb on Wed Sep 05, 2018 9:40 am, edited 4 times in total.

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Re: Superbrain #1 : The ratty one

Post by jonb » Wed Sep 05, 2018 10:00 am

Here's what the old plug looks like. It's wired safely enough, except:
  • The fuse is 13A but really should be 3A.
  • The live is white although someone helpfully marked it with red!

IMG_4905.jpg
How not to wire a plug...

Oh dear, oh dear.

:roll:
Last edited by jonb on Wed Sep 05, 2018 10:01 am, edited 1 time in total.

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Re: Superbrain #1 : The ratty one

Post by Elminster » Wed Sep 05, 2018 10:19 am

I have a couple of switched PSU, designed for things like LED lighting but very useful. I have a 200W 36V and a 40w 12v for my DIY project bench.

Got job on the caps, I have a monster CAP on my SWTPC which scares me. Probably keep its charge for a few thousand years.

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Re: Superbrain #1 : The ratty one

Post by jonb » Wed Sep 05, 2018 10:49 am

Thanks Elminster!

The missing cap turned up today so I fitted it and connected the PSU 5v and 12v outputs to a test load:

IMG_1140.JPG

..then adjusted the 5v line to 5v.. The trimmer pot is very loose - I'll have to put something on it to stop it turning, once I've set the voltage up right for the board. It's ready to go back into the chassis now. :D

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Re: Superbrain #1 : The ratty one

Post by Elminster » Wed Sep 05, 2018 11:09 am

jonb wrote:
Wed Sep 05, 2018 10:49 am
The trimmer pot is very loose - I'll have to put something on it to stop it turning, once I've set the voltage up right for the board.
loctite for bolts would do it. Or blue tac :)

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Re: Superbrain #1 : The ratty one

Post by 1024MAK » Wed Sep 05, 2018 11:28 am

Best if whatever you use is not too runny...

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Re: Superbrain #1 : The ratty one

Post by jonb » Wed Sep 05, 2018 11:40 am

1024MAK wrote:
Wed Sep 05, 2018 11:28 am
Best if whatever you use is not too runny...
Yeah... like, "BOOM!"..

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Re: Superbrain #1 : The ratty one

Post by 1024MAK » Wed Sep 05, 2018 12:09 pm

I don't normally bother to "seal" trimmers or presets on my equipment, but in the past I have used just a small drop of the gooey liquid paper (cheap brand of 'Tipex').

Mark

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Re: Superbrain #1 : The ratty one

Post by jonb » Sun Sep 16, 2018 9:24 am

OK, there is an update to this story and it's not great..

It's going back to CCH on the 24th, so I had to reassemble it as I'd been using it to power Alan's SB Main board (see "Superbrain #2: The Board"). This is when I discovered that the drives seemed rather flaky. It's the first time I've tried to run it with both drives since the board failed last time. The symptoms are that B: won't read floppies. I suspected head alignment, so swapped them around. Still not working. Then I tried a different cable without success. Eventually I plugged in a known good pair of BBC drives, set to 40 track, and got the same problem. This means, sadly, we are back to the main board, and in particular the area around CPU2 that communicates with the FDC. I have already replaced one 2114 (it was the reason CPU1 couldn't read the ROM properly) and I suspect there might be a problem with the other one. Only way to tell is to do a memory test with the ICE in CPU2's socket. Here we go again!
Last edited by jonb on Sun Sep 16, 2018 10:43 am, edited 1 time in total.

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Re: Superbrain #1 : The ratty one

Post by jonb » Sun Sep 16, 2018 11:01 am

CPU2's memory map is a bit odd:

Code: Select all

0000000000000000111111111111111122222222222222223333333333333333
0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF
RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR  RR  RR  RR  RR  RR  RR  RR  RR
OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO  WW  WW  WW  WW  WW  WW  WW  WW
00000000000000000000000000000000  22  22  22  22  22  22  22  22
01220122012201220122012201220122  22  22  22  22  22  22  22  22
I expected to see ROM in the first 1/4 as you do when looking at CPU1's map (because the same ROM is paged in when CPU2 is active, or should be). Then we see a bunch of repeated RAM segments starting at 8200. What's odd here is that CPU2 has 1k of SRAM only and it is supposed to start at 8800 and end at 8BFF. That would be 28 on the ICE "md" output shown above, I think, and yet there is a hole there.

When testing the address range 8800-8BFF I get no errors, though. :-k

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Re: Superbrain #1 : The ratty one

Post by jonb » Sun Sep 16, 2018 11:17 am

Further investigation, this time of the ROM again. From CPU2's perspective, it looks like this:

Code: Select all

0000 00             NOP
0001 00             NOP
0002 00             NOP
0003 DB 0A          IN A,(0A)
0005 2F             CPL
0006 3D             DEC A
0007 28 1C          JR Z,0025
0009 21 00 04       LD HL,0400
000C 11 00 C0       LD DE,C000
000F 01 00 04       LD BC,0400
0012 ED B0          LDIR
0014 01 00 04       LD BC,0400
0017 2B             DEC HL
0018 1B             DEC DE
0019 1A             LD A,(DE)
001A BE             CP (HL)
001B 20 EC          JR NZ,0009
001D 0B             DEC BC
001E 78             LD A,B
I know this is wrong. The same ROM, when viewed from CPU1, looks quite different:

Code: Select all

;
;	INTERTEC SUPERBRAIN EPROM (2716)
;
;	SEE LOC 006D FOR PATCHING 35 CYLS TO 40 ETC.
;
;	DISASSEMBLED Mon Oct 10 02:10:42 1994 BY WARREN GAY.
;
	LD	A,(08800H)	; 0000
	CP	055H		; 0003
	JP	NZ,00013H	; 0005
;
	LD	A,(08801H)	; 0008
	CP	0AAH		; 000B
	JP	NZ,00013H	; 000D
;
	JP	00021H		; 0010
;
;	MAIN CPU CODE... SYSTEM INITIALIZATION.
;	COPY ROM 0400 CODE TO C000, THEN JP C006
;
L0013:	LD	HL,00400H	; 0013
	LD	DE,0C000H	; 0016
	LD	BC,00400H	; 0019
	LDIR			; 001C
	JP	0C006H		; 001E
I have no idea how the machine is managing to boot, but the effect is to jump to 0025 instead of 0021. This section of code initialises certain addresses:

Code: Select all

L0021:	LD	SP,08BFFH	; 0021	STACK POINTER
	LD	A,000H		; 0024
	LD	(08800H),A	; 0026	ZERO 8800
	LD	(08801H),A	; 0029	ZERO 8801
	LD	(08807H),A	; 002C	ZERO 8807
	LD	(08806H),A	; 002F	ZERO 8806
;
;	ACCESS RAM FROM MAIN Z80?
;
	OUT	(10H),A		; 0032	SEND ZERO -> PORT(10H)
	LD	A,(002FH)	; 0034	?
	OUT	(08H),A		; 0037	RESTORE FDC CMD????
;
;	WAIT FOR A MAIN Z80 REQUEST (POLL 8807 BYTE)
;  (ETC)
;
Somehow it is running enough code to boot. It's also able to display the "insert disk" message. Am I barking up the wrong tree?

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Re: Superbrain #1 : The ratty one

Post by jonb » Sun Sep 16, 2018 11:23 am

Substituting the 4.03 ROM (a TMS2716) for my EEPROM carrier board (with v3.1 ROM installed) yields a better result:

Code: Select all

OK ===> l
0000 3A 00 88       LD A,(8800)
0003 FE 55          CP 55
0005 C2 13 00       JP NZ,0013
0008 3A 01 88       LD A,(8801)
000B FE AA          CP AA
000D C2 13 00       JP NZ,0013
0010 C3 21 00       JP 0021
0013 21 00 04       LD HL,0400
0016 11 00 C0       LD DE,C000
0019 01 00 04       LD BC,0400
001C ED B0          LDIR
001E C3 06 C0       JP C006
0021 31 FF 8B       LD SP,8BFF
0024 3E 00          LD A,00
0026 32 00 88       LD (8800),A
0029 32 01 88       LD (8801),A
002C 32 07 88       LD (8807),A
002F 32 06 88       LD (8806),A
0032 D3 10          OUT (10),A
Looks familar...

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Re: Superbrain #1 : The ratty one

Post by jonb » Mon Sep 17, 2018 8:31 am

...however, it still does not allow B: to read files...

Time to recap:
  • Both drives work when configured as A:.
  • The only difference (electronically) between reading A: and reading B: is the DS0 / DS1 signal (which selects the drive). On attempting to access B:, the drive light comes on and the motor spins up (in other words, it is being selected properly by DS1).
  • CPU 2's memory looks to be OK, and it's reading the ROM correctly (CPU 2 manages the FDC on the Superbrain).
  • Swapping out the FDC had no effect.
  • Swapping out the drive cable had no effect.
  • Attempting to access B: with a completely different set of drives (the known good BBC Micro unit) had no effect.
Wondering what I've missed here. Must be something... :-k

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Re: Superbrain #1 : The ratty one

Post by 1024MAK » Mon Sep 17, 2018 9:06 am

Does this system make use of a Drive Ready/Disk Changed (/RDY, pin 34) signal?

Or it’s timed out waiting for another signal from the drive?
Pin 26 /TRK00 Track 0
Pin 8 /INDEX Index

If one of these signals is missing, would this cause these symptoms?

Mark

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Re: Superbrain #1 : The ratty one

Post by jonb » Mon Sep 17, 2018 9:33 am

Hi Mark

I think that as A: works perfectly then all signals are OK. I tried to swap drives again today and the B: drive wouldn't boot. Funny, as I definitely tried it before. Maybe I can stick a BBC drive in there to test.

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