a2000 problem.

[nahoo7]

I have an a2000 with 68030 accelerator,scram2000 scsi card with 850mb hd and plextor cdrom attached,386 bridgeboard,flickerfixer card wb 3.1.
My problem is after about 5mins of running the computer, the screen becomes corrupted with all different coloured pixels on the screen and eventually freezes.
If I switch it on after about 30 to 40 mins it works again and repeats this process
I have replaced cia chips and denise chip but this didnt change anything also reformatted hd.
The same thing happens using the video output so the flicker fixer isnt the problem,I cant seem to find any heat problems  ie none of the chips seem to be overheating.
The ram is reported correctly so I dont think the ram is corrupted.
I think it may have something to do  with the power supply but am only guessing any ideas?regards nahoo7.

[CLS2086]

Hi,
dying PSU or a virus...

[JimS]

try pushing down on the agnus in it's socket, and check the socket for cracks.

[JoeMuc2006]

Might also be a thermal problem as your A2000 always does well for some time, and regularly fails after some time. Especially flicker fixers / scan doublers get unexpectedly hot. I have an external flicker fixer for my A500 and once nearly burned my fingers on it. I think I'll provide it with a fan before using it next time... it was too expensive to just burn it. No idea why the manufacturer didn't think of that.

Or, the PSU might be overloaded with all the hardware you have. If it is not a heat problem, try to run the machine with less expansion boards and see whether it is stable then. I'd first remove the 386 board, then check stability, if it still fails, remove the flicker fixer and try again. If you can, exchange the PSU with one from another A2000.

[quenthal]

Yeah, check out every chip on a socket that they are firmly in place. Run your amiga without cover with fresh air (from a desk cooler or something like that) and check if it runs longer then?

[nahoo7]

hi thanks for your replies have checked all chips are properley seated agnes chip looks okay .
I dont have another psu ,do have an atx psu  but it doesnt have a switch on the back does that matter if I use that in the a2000.
Can I put a switch in the lead that carries the tick signal to power up or switch it on and off at the wall.

[Amiga4k]

Suggest you power the hard drive and CD-ROM drive from the ATX psu for a test. This takes the strain off the A2000 psu. If the A2000 acts normally or falters, then your sure about the power supply being a problem. (Hope that sounds right?).
If you have a voltmeter, add a "Y" power plug so you can check check the voltages on the drive line during operation, and especially when it falters.
The drive connector on the A2000 psu is wired as follows:
Orange Blue Blue Yellow
12VDC---Ground----5VDC
If the A2000 psu is the problem, I would then suggest you remove the power supply, open the case, and clean it. Also check the fan, to see if it's burdened with grim, and actually turns.


Taken from this source:
AMIGA TROUBLESHOOTER - PART 2: A500/A2000
THE AMIGA TROUBLESHOOTER IS COPYRIGHTED © 1993 IAN PERRY.
HTML conversion by Thomas Unger 2002. View the original document.
VIDEO PROBLEMS

   1. Screen brakes up (scrambles) after running for 15 to 30 minutes.
      Probable causes are:

          * 8370 - 8372/8375 U2 Fat Agnus (U101 A2000)
          * 8362 U4 (U201 A2000)
          * U2 Socket (U101 A2000)

   2. System locks up when double clicking icon:

          * 8370/8375 U2 (U101 A2000)
          * 8362 U4 (U201 A2000)
          * 8520 U7 Odd CIA (U300 A2000)
          * 74LS32 U37 (U302 A2000)

   3. Scrambled video loss of composite sync.

          * 8370 - 8372/8375 U2 (U101 A2000)
          * 74HC245 U41 (74HCT244 U205 A2000)
          * RP403

   4. Incorrect colors (loss of red, green or blue):

          * 8362 U4 (U201 A2000)
          * 74HC245 U40-U41 (74HCT244 U205-U206 A2000)
          * Video Hybrid

   5. No video (black screen)

          * R405 4.7 ohm resistor
          * R406 4.7 ohm resistor
          * 8362 U4 (U201 A2000)
          * Video Hybrid
          * 74HC245 U40-U41 (74HCT244 U205-U206 A2000)

[Olecranon]

One thing to keep in mind.  If your trying to use an ATX power supply to run your CDROM and HARDDRIVE, you need to force the power supply on (since it doesn't have a switch).  You need to run a small loop of wire from the GREEN wire to any BLACK wire on the motherboard connector.  

I would suggest taking a small length of wire, strip both ends, and plug the expose ends into the corresponding places on the motherboard connector of the power supply.

[nahoo7]

okay thanks for that info will check it all out tonight.
As suggested with the scrambling screen looks like it may be the agnus chip.
The only spares I have are from a500 which wont be 1mb of chip ram will that make a difference will have to find a chip puller as I live in Australia anybody know where Ican get one?cheers.

[Amiga4k]

I am including a list of Agnus chips (researched it). I do not know whether your system is PAL or NTSC (what are Australian systems anyway?). Radio Shack has chip pullers. You need to get the tiny hooks down into the opposing notches, and pull up evenly.

Agnus (512K)   8370    318070-01   A500 (NTSC), A2000 (NTSC)
Agnus (512K)   8371    318071-01   A500 (PAL), A2000 (PAL)
Agnus (1MB)     8372      318069-01       A2000
Agnus (1MB)   8372    318069-02   A500 (PAL), A2000 (PAL) Regular Type

Agnus (1MB)    8372A     318069-02         A500
Agnus (1MB)    8372A     318069-029   A500 (PAL), A2000 (PAL) (changed after some damage)
Agnus (1MB)   8375     318069-17   A500 (NTSC), A2000 (NTSC)

[nahoo7]

Hi attempted to use an atx psu in my a2000 using direction from amiga psu guide and no go.
Followed directions exactly,the only difference is that pin 14 on the atx psu that I have tried is black and the green wire is pin 4 on one and pin 17 on the other.
Both psu were working so must be wiring wrong any ideas cheers.

[dbrads]

I had a simmilar problem about 10 years ago with my original A2000, it turned out to be a bad KS2.04 rom that I fitted.
I called the supplier, they sent a replacement and it cured the problem. If you have a spare KS rom maybe it would be worth a try.

[nahoo7]

Ok thanks for the reply will try that cheers.

[Amiga4k]

You never did say what the voltages were on the power supply.

[nahoo7]

sorry  no I dont have a volt meter so I cant check it out.
Anyway I put the old power supply back in and turned it on and it started up with coloured flecks on the screen.
Rebooted and then got screen screen so I think I will purchase another agnus chip and see what difference that makes.