G-Force 030 Combo hangs

[jcm]

Hi all,

first, I apologize if this has been covered already.  

I have a GVP G-Force 030 Combo with a 68030 at 40Mhz. I got it used and it worked fine for 7-8 months when the A2000 started to hang. First, it was maybe once a week, then once a day and then once an hour.  And then, it would not boot at all.  A couple of friends had a look at it and when we changed the clock crystal from 40MHz to 25MHz, it boots but hangs after 5-10 seconds. Changing the CPU produces the same result.

Since there are not schematics to get for this card a friend who is quite competent when it comes to electronics has had a look and has guessed that it's the PAL circuits are damaged, which apparantly happens after a while when you overclock the thing. Another friend suggested it may be the MACH circuit that's damaged.

Anyone have any idea what the problem may be?  

Thanks,

Joacim

[jcm]

Which GVP 030 Combo is this? GVP released three of them, a 25Mhz entry-level version, a 040 mid-level version, and a 50Mhz high-end version. I guess you probably have the 25Mhz version?

Does the Amiga boot without the board? What about the power supply? Did you try the GVP card in another system?

It's the series II 40Mhz. The A2000 boots fine without the GVP board and we have tried the GVP board in another A2000 with the same results.

We have also checked the PSU and it is fine. I suspect the GVP card has been overclocked by a previous owner.

[jcm]

Tried it with the memory removed?

Is this one of the ones with memory chips soldered directly to the board? I remember someone else having a problem that pointed to those a while back. Not sure if it ever got resolved?

Also, have you tried cooling it? (fan, run with the case open, add a heatsink, etc.)

Yes, it's the one that has 4MB pre-installed.  I have tried to remove the additional RAM I had installed and set all jumpers accordingly. No difference I'm afraid.

[jcm]

If it's the same 1 I have then it should have 4MB soldered and room for 3 more. Is there anything new on the system? remove all cards and go with just the soldered memory.

There is a Golden Gate II and a NE2000 network card installed. Have tried to remove all other cards and the result is the same I'm afraid.

[jcm]

I got some time today to fiddle around some more. I removed the two 4MB RAM sticks and set jumpers accordingly. I also disabled SCSI harddrive present.

With 40Mhz clock crystal installed, system at least boots to insert-diskette-screen but CPU, FPU and the thing at RP2 (see enclosed photo) gets crazy hot.

[ATTACH]5535[/ATTACH]

With 25Mhz clock crystal installed, CPU and FPU stay at reasonable temperature levels but the RP2 thing gets crazy hot when I try to boot from a workbench diskette.

So - progress but still not progress I suppose.

[ATTACH]5536[/ATTACH]

I forgot to mention that I had the memory buffer chips (I think it was, anyway) replaced as my electronics friend thought they was the source of the problem. They are in the red box in the other photo attached to this post.

[jcm]

I spoke too soon on this. I removed the FPU and lo and behold, everything boots and the circuits stay cool.

Until I tried to do some diagnostics and realise that the A2000 isn't actually using the GVP 030 Combo-card at all.  Put everything back and the machine indeed still boots but it still doesn't recognise the GVP 030 Combo is even installed.

I'm totally stumped here, but obviously something is very broken.

Sad face, etc.

[jcm]

RP2 is a resistor pack, and shows damage. It has been getting hot all of it's life, probably. These are typically used to pull a signal up to (+5V) or down to (GND) if no other part of the system is directly driving the signal line at the time. On the inside they are very simple, just a bank of resistors lined up to one common rail. Saves a lot of connections than using individual resistors.

Typically, some RP designs have lower or higher resistance values than are necessary for continuous operation. Also, if they are sinking more power (Volts X Amps = Watts) then they were designed for, they will get very very hot and eventually some of the individual resistors in them start burning out. Resistors have a wattage value. If they sink more current and draw more power (watts) than they are rated for, they will die, sooner rather than later.

The snag with resistor packs is, every resistor in one has a similar resistance. Sometimes you want a bit higher, to reduce the amount of power being drawn. Swapping out just one resistor isn't possible without hacking the motherboard. If you do replace RP2, try it 2 ways - one with the same resistance values, one with about double that or less. The double one will run cooler, but might not be able to "assert" the line correctly.

You might find some of the logic chips around that area, which connect the fast RAM sockets to the rest of the system, have gone bad. You can get 74 series chips in both TTL and CMOS. Most equipment was fitted with TTL. CMOS take way less power and does the same job, but requires careful handling as it is static sensitive (this is an issue when noobs start poking around with hardware).

What revision of A2000 are you using it on? Problem might not be the card, it might be a mod done to bring early rev 4 boards up to rev 6 standard. Or there might be issues with both Amiga motherboard and card daughterboard.

The root cause I think is, accelerators need slow downs when talking to or reading from the Amiga custom chips, or chip RAM. That part of the bus only goes at 7MHz (AGA goes 14MHz), so accelerators have to slow down access to those areas, or the information gets garbled on transfer. For some reason, that used to work, but does not anymore.

The problem is vastly reduced on the A3000 and A4000, which were ALWAYS designed for faster CPUS to access the Amiga parts of a system without a hitch. OK, sometimes you have to plug in newer Busters, but the design side was there from the start. Those were designed asynchronous from the ground up. A2000s just were not, it was something they were adapted to by modification.

I got the 4.3 revision in my A2000. As I mentioned previously, the GVP 030 Combo ran fine for months in this A2000 but I guess a 30 year old computer can brake too.  

[jcm]

Can't look at mine right now but as I recall the FPU is a 25Mhz one. If that was overclocked it may have been damaged.

Sounds like a reasonable explanation. I can't find any info in the documentation about disabling the FPU entirely after removing it.  Any secret jumper setting I missed or didn't understand?

[jcm]

All that stuff in the yellow box is socketed FOR A REASON. It was designed to be replaced in time.

It can be difficult to source replacements in that package, at least you have all the chip numbers written on the top of them.

4.3? Yeah, time to hack it up to 6. Which was what happened at the time, some of the mods may have gone bad, and the card is actually OK.

Yeah the GAL/PAL chips are NOT easy to come by and they are locked so whatever code they contain can't be read off the chips.  Thanks so much, GVP.

I guess I'll just have to sell this card and the RAM and get something else for this A2000.

[jcm]

I'm sure you've already seen this, but I believe it might be more informative regarding jumper positions than what the factory provided:

http://members.iinet.net.au/~davem2/overclock/combo.html

Interestingly, seems the option to set frequencies and add a wait state are configurable by jumpers--I wonder if the PALs really were different for factory 50MHz cards?

Great link, hadn't seen that.  Thanks!

[jcm]

Pat brings up a good point.  If you're trying it on Rev. 4 A2000 boards, any difference if you try it on a >Rev. 6 series board?  The newer models have much cleaner signals.  Slight chance but maybe worth checking out?

I don't have a rev. 6 board to try it with unfortunately.