Strange Problem Amiga 2000

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Strange Problem Amiga 2000

Gerrit Heitsch

This might not be quite the right place, but the Amiga was made by
Commodore after all...

Anyway, I have an Amiga 2000, PAL, the early model that uses a
multilayer board and the A1000 chipset, that exhibits a strange problem.

The system is complete, including the memory card for the MMU/CPU-Slot
which has been expanded to 1 MB and passes the memory test of the
systest disk. I also own a another such card which also works.

There are 2 floppy drives, with DF0: having been replaced with a GOTEK
floppy emulator using the latest FlashFloppy Firmware 0.9.29a.

The problem:

When you turn the Amiga on, it always starts and shows the screen
prompting you to insert a bootable disk. Kickstart is 1.3 (got it this
way). You can have it sit here as long as you want, makes no difference.
If you then plug in a USB stick with a bootable image on it, the system
will attempt to boot and, in most cases, crash with a GURU error of
0000000B.00000000 or 0000000A.00C0xxxx. Taking the GOTEK out and putting
DF0: back in, booting from a real disk only makes the crash less likely,
it doesn't eliminate it.

If the system does not crash but boot, it will then happily run for
hours on end doing whatever you ask it to do.

What I tried:

1) Suspected the PSU, replaced all caps on the secondary side. Measured
the caps I took out (most were from FRAKO), all still good. Primary
filter caps (made by Roederstein, ROE) were only checked, but are also
still as good as new. PSU is made by 'ISMET', delivers up to 200W and
shows no problem powering on with a dual filament lightbulb as a load
for +5V and +12V. Load when on with the bulb is about 60W, more while
it's still cold. New caps didn't solve the problem.

2) Suspected the KS 1.3 ROM and tried a different one. Didn't help.

And now it gets weird.

3) Decided to try a different CPU, Original one is a MC68000P8 from
1987. Tried another MC68000P8, a MC68000P12 and a 68000 from Thompson.
No dice. But when using a 68000 made in 1992 by ST, the crashes
disappeared. Do I have 4 damaged CPUs? Seemed unlikely. All 68000 are
the HMOS kind, none of them is CMOS. For grins, I tried an MC68010L10 as
well. No change.

4) Decided to try one of my KS 1.2 ROMs. No more crashes with any of the
CPUs I own. Tried a second KS 1.2 ROM. same result.

5) Tried the solutions from 3) and 4) multiple times to make sure I
didn't just have a contact problem in one of the sockets. Always behaved
as described above.


Anyone having an idea what might be the cause? The GOTEK delivers the
data faster (meaning less latency, datarate is, of course, the same as
with a floppy drive). Were there any changes to the trackdisk.device
that between 1.2 and 1.3 that might explain this behaviour? And why does
the one 68000 from ST solve it?

Since this A2000 will not be expanded but mostly used for games, I can
live with KS1.2, but some part of me hates unexplained errors of the
'all parts work by themselves, but not when used together' kind.

  Gerrit


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Re: Strange Problem Amiga 2000

Rainer Buchty
On Sat, 6 Oct 2018, Gerrit Heitsch wrote:

> Anyone having an idea what might be the cause? The GOTEK delivers the
> data faster (meaning less latency, datarate is, of course, the same as
> with a floppy drive).

There's at least one machine, the PPG Waveterm, that requires a pulse
stretcher to "digest" the GOTEK read-data output. If that's also the
underlying issue here, you might want to attach a monoflop there to make
the 1-pulses a tad longer.

Rainer

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Re: Strange Problem Amiga 2000

Gerrit Heitsch
On 10/06/2018 06:38 PM, Rainer Buchty wrote:

> On Sat, 6 Oct 2018, Gerrit Heitsch wrote:
>
>> Anyone having an idea what might be the cause? The GOTEK delivers the
>> data faster (meaning less latency, datarate is, of course, the same as
>> with a floppy drive).
>
> There's at least one machine, the PPG Waveterm, that requires a pulse
> stretcher to "digest" the GOTEK read-data output. If that's also the
> underlying issue here, you might want to attach a monoflop there to make
> the 1-pulses a tad longer.

Well, once I get over the initial possibility of a crash, everything
loads and writes fine. And with a KS 1.2 ROM I don't have any problems
at all. That kind of indicates that the data delivered by the GOTEK is
no problem for PAULA to digest and decode.

  Gerrit




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Re: Strange Problem Amiga 2000

MiaM
Den Sat, 6 Oct 2018 19:20:38 +0200 skrev Gerrit Heitsch
<[hidden email]>:

> On 10/06/2018 06:38 PM, Rainer Buchty wrote:
> > On Sat, 6 Oct 2018, Gerrit Heitsch wrote:
> >
> >> Anyone having an idea what might be the cause? The GOTEK delivers
> >> the data faster (meaning less latency, datarate is, of course, the
> >> same as with a floppy drive).
> >
> > There's at least one machine, the PPG Waveterm, that requires a
> > pulse stretcher to "digest" the GOTEK read-data output. If that's
> > also the underlying issue here, you might want to attach a monoflop
> > there to make the 1-pulses a tad longer.
>
> Well, once I get over the initial possibility of a crash, everything
> loads and writes fine. And with a KS 1.2 ROM I don't have any
> problems at all. That kind of indicates that the data delivered by
> the GOTEK is no problem for PAULA to digest and decode.

I might had missed something, but did this problem appear when you
installed the GOTEK and was it known to work before you installed the
GOTEK?

If it's not really GOTEK related, it could be some kind of timing issue
related to whatever happens on the (cpu) bus.

Are this revision of Amiga 2000 really known to generally "work"? (Of
course they did work as they were delivered back then, but are various
expansion cards and upgrades known to be compatible)?

--
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Re: Strange Problem Amiga 2000

Gerrit Heitsch
On 10/06/2018 07:33 PM, Mia Magnusson wrote:

> Den Sat, 6 Oct 2018 19:20:38 +0200 skrev Gerrit Heitsch
> <[hidden email]>:
>> On 10/06/2018 06:38 PM, Rainer Buchty wrote:
>>> On Sat, 6 Oct 2018, Gerrit Heitsch wrote:
>>>
>>>> Anyone having an idea what might be the cause? The GOTEK delivers
>>>> the data faster (meaning less latency, datarate is, of course, the
>>>> same as with a floppy drive).
>>>
>>> There's at least one machine, the PPG Waveterm, that requires a
>>> pulse stretcher to "digest" the GOTEK read-data output. If that's
>>> also the underlying issue here, you might want to attach a monoflop
>>> there to make the 1-pulses a tad longer.
>>
>> Well, once I get over the initial possibility of a crash, everything
>> loads and writes fine. And with a KS 1.2 ROM I don't have any
>> problems at all. That kind of indicates that the data delivered by
>> the GOTEK is no problem for PAULA to digest and decode.
>
> I might had missed something, but did this problem appear when you
> installed the GOTEK and was it known to work before you installed the
> GOTEK?

As I wrote... The GOTEK only makes it more likely to happen, but it also
happens with a normal floppy drive and disk.


> Are this revision of Amiga 2000 really known to generally "work"? (Of
> course they did work as they were delivered back then, but are various
> expansion cards and upgrades known to be compatible)?

Well, this version is using an early version of the Zorro bus, the whole
logic implemented in PALs and TTLs and not a BUSTER chip as in the later
A2000 where AGNUS came in 84pin PLCC instead of 48pin DIP. There are
some problems with the bus protocol on the Zorro slots.

The main difference is that if you use a CPU card with this A2000, you
have to remove the 68000 from the mainboard.

But then, I am not using a CPU card or any kind of expansion card in it
and I either have to use the right CPU (the ST 68000) when using KS 1.3
or just use KS 1.2 with any 68000 to have no problems at all.

  Gerrit





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Re: Strange Problem Amiga 2000

Francesco Messineo
On Sat, Oct 6, 2018 at 7:45 PM Gerrit Heitsch <[hidden email]> wrote:

>
>
> Well, this version is using an early version of the Zorro bus, the whole
> logic implemented in PALs and TTLs and not a BUSTER chip as in the later
> A2000 where AGNUS came in 84pin PLCC instead of 48pin DIP. There are
> some problems with the bus protocol on the Zorro slots.
>
> The main difference is that if you use a CPU card with this A2000, you
> have to remove the 68000 from the mainboard.
>
> But then, I am not using a CPU card or any kind of expansion card in it
> and I either have to use the right CPU (the ST 68000) when using KS 1.3
> or just use KS 1.2 with any 68000 to have no problems at all.

I don't know what type of chip "hosts" the Kickstart (I'm not so
expert on Amigas), but did you try to copy the KS 1.3 on different
EPROMs?
Sounds like some weird decoupling/logic-threshold/rail-bouncing
problem. I would have a good look at the CPU bus with a logic
analyzer.

Frank

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Re: Strange Problem Amiga 2000

Gerrit Heitsch
On 10/06/2018 07:52 PM, Francesco Messineo wrote:

> On Sat, Oct 6, 2018 at 7:45 PM Gerrit Heitsch <[hidden email]> wrote:
>>
>>
>> Well, this version is using an early version of the Zorro bus, the whole
>> logic implemented in PALs and TTLs and not a BUSTER chip as in the later
>> A2000 where AGNUS came in 84pin PLCC instead of 48pin DIP. There are
>> some problems with the bus protocol on the Zorro slots.
>>
>> The main difference is that if you use a CPU card with this A2000, you
>> have to remove the 68000 from the mainboard.
>>
>> But then, I am not using a CPU card or any kind of expansion card in it
>> and I either have to use the right CPU (the ST 68000) when using KS 1.3
>> or just use KS 1.2 with any 68000 to have no problems at all.
>
> I don't know what type of chip "hosts" the Kickstart (I'm not so
> expert on Amigas), but did you try to copy the KS 1.3 on different
> EPROMs?

It's a 40pin Mask ROM, 16 bit wide. You can get EPROMs for it, but I
don't have any and I also don't own a programmer for them.

  Gerrit


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Re: Strange Problem Amiga 2000

MiaM
In reply to this post by Francesco Messineo
Den Sat, 6 Oct 2018 19:52:23 +0200 skrev Francesco Messineo
<[hidden email]>:
> On Sat, Oct 6, 2018 at 7:45 PM Gerrit Heitsch
> <[hidden email]> wrote:
> >
> >
> > Well, this version is using an early version of the Zorro bus, the
> > whole logic implemented in PALs and TTLs and not a BUSTER chip as
> > in the later A2000 where AGNUS came in 84pin PLCC instead of 48pin
> > DIP. There are some problems with the bus protocol on the Zorro
> > slots.

Well, the "protocol" itself is mostly just the autoconfig process,
which is super simple to implement (and most likely not a problem). The
problems it might have seems more likely to be of the analogue kind,
i.e. reflections or similar.

That might, or might not, be an issuie in your case.

> > The main difference is that if you use a CPU card with this A2000,
> > you have to remove the 68000 from the mainboard.
> >
> > But then, I am not using a CPU card or any kind of expansion card
> > in it and I either have to use the right CPU (the ST 68000) when
> > using KS 1.3 or just use KS 1.2 with any 68000 to have no problems
> > at all.
>
> I don't know what type of chip "hosts" the Kickstart (I'm not so
> expert on Amigas), but did you try to copy the KS 1.3 on different
> EPROMs?

One problem is that almost no one who's not an "Amiga kickstart burner"
has those EPROM's in their good-to-have junk box. They are 16-bit and
therefore much rarer.

> Sounds like some weird decoupling/logic-threshold/rail-bouncing
> problem. I would have a good look at the CPU bus with a logic
> analyzer.

Agreed, but maybe an oscilloscope would be better, as it's not unlikely
that the issue needs a faster tool than most logic analyzers.

--
(\_/) Copy the bunny to your mails to help
(O.o) him achieve world domination.
(> <) Come join the dark side.
/_|_\ We have cookies.

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Re: Strange Problem Amiga 2000

Gerrit Heitsch
On 10/06/2018 08:52 PM, Mia Magnusson wrote:

> Den Sat, 6 Oct 2018 19:52:23 +0200 skrev Francesco Messineo
> <[hidden email]>:
>> On Sat, Oct 6, 2018 at 7:45 PM Gerrit Heitsch
>> <[hidden email]> wrote:
>>>
>>>
>>> Well, this version is using an early version of the Zorro bus, the
>>> whole logic implemented in PALs and TTLs and not a BUSTER chip as
>>> in the later A2000 where AGNUS came in 84pin PLCC instead of 48pin
>>> DIP. There are some problems with the bus protocol on the Zorro
>>> slots.
>
> Well, the "protocol" itself is mostly just the autoconfig process,
> which is super simple to implement (and most likely not a problem). The
> problems it might have seems more likely to be of the analogue kind,
> i.e. reflections or similar.
>
> That might, or might not, be an issuie in your case.

All interesting signals (address, data and some control signals) for the
Zorro slots have to go through a bunch of 74LS245, so reflections on the
long traces for the slots can't be the issue.

  Gerrit


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Re: Strange Problem Amiga 2000

silverdr@wfmh.org.pl
In reply to this post by Gerrit Heitsch

> On 2018-10-06, at 14:41, Gerrit Heitsch <[hidden email]> wrote:
>
> This might not be quite the right place, but the Amiga was made by Commodore after all...
>
> Anyway, I have an Amiga 2000, PAL, the early model that uses a multilayer board and the A1000 chipset, that exhibits a strange problem.
>
> [...]
>
> Since this A2000 will not be expanded but mostly used for games, I can live with KS1.2, but some part of me hates unexplained errors of the 'all parts work by themselves, but not when used together' kind.

It's a long shot but I twice solved "illogical" (surprisingly also with A2000) issues by finding and replacing (with FB) partially faulty EMI filters. I don't have A2K schematics at hand now (does this revision have Gary?) but since it looks somehow related to floppy circuits (Gotek vs. regular floppy) and possibly a sort of edge-case timing issue - I'd possibly check also around Gary and floppy lines, which can have some EMI filters around the external connector.

--
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