How to fix the A1200 ? - info wanted

I've heard there are a few hardware faults atleast on some A1200 motherboards.

Does anyone know a good source that gives information about these ? ( If there are
more of these & what motherboard revisions these concern! )

I know the PCMCIA Reset Fix & "MotherboardMod"-file I've pasted to the end.

Concerning the "MotherboardMod", I didn't locate E123C & E125C on my AT A1200
Rev 1D.4 ( Budgie Rev -01) motherboard ? Where are them ? ( under the RF-modulator
perhaps? )


!!!Apparently there's also " ALICE TIMING & VIDEO TEARING FAULT"  - Does anyone know
what this/these are & how to fix them ? Is the pasted text relevant ?



If in better knowledge than me, please reply. I'm trying to get my ZII-expansion working
- it just might be the A1200 timing errors that stop it from working or it's broken
itself (most propably)     ( RBM Towerhawk Onboard Ex )


Cheers

Kenneth Ekqvist


----

Motherboard Modifications

As with most machines, the A1200 left the factory with a few design flaws. Most
of these won't affect anybody, but they can stop some accelerators from working.
Here are the modifications that should be made for a "perfect" A1200;


REV 1D.4
  Budgie REV -01
   > Remove E123C and E125C from the A1200 motherboard
 
  Budgie REV -02
   > Remove E123C and E125C from the A1200 motherboard
   > Remove XR358 470 ohm pull-up resistor
   > Add 470 ohm pull up resistor at pin 43 of U, ie the Alice chip


REV 2B
  Budgie REV -01 and -02
   > Remove E123C and E125C from the A1200 motherboard
   > Add 470 ohm pull-up at pin 43 of U2, ie the Alice chip
   > Change R118 from 470 ohm to 220 ohm

----

[Stedy]

Hi,

Re: the timing fix,

E123C, E125C are on the underside of the A1200 motherboard near the Alice chip (U2)

I have a Rev2B A1200 and Apollo 1240, I did not do all of the rev 2B mod, I removed R118 and did not replace it and left off the 470 Ohm pull up, all worked fine!

removal of E123/E125 correct a timind delay of about 8 Ns on the 7MHz and CDAC signals, which link to Budgie (system clock/ram controller)

Note sure about what the ALICE timing and video tearing fault is. It could in part be to do with the general motherboard mod. I think there were different filter components on some amiga motherboards for the video.

Hope this helps,

Ian

[Ilwrath]

!!!Apparently there's also " ALICE TIMING & VIDEO TEARING FAULT" - Does anyone know what this/these are & how to fix them ? Is the pasted text relevant ?

Yes, there is indeed an Alice video tearing problem with early A1200's.  I don't know if it went to later versions, I don't believe so, but I've owned three (!) over the years which have displayed the problem, and I've seen two more do it.  There are certain conditions which will cause it to be MUCH more pronounced than others.  Here's the conditions that they all share:

The Configuration:
* Early A1200 - (Rev 1D)
* Baseboard FastRAM (usually more visible if FastRAM is on an early A1200 accelerator, like the GVP A1230 series 1, or the VXL - but I've also seen the display flicker on a simple FastRAM + clock card)
* Screen display set to a fast pixel clock.  (Usually only Hi-Res/NoFlicker screens, such as DblNTSC, DblPAL, or Super72 will be affected -- Turning back to regular NTSC will lower the visible artifacting!)
* Most machines have also had some use of the PCMCIA slot (squirrel SCSI, RAM drive, or Network card) -- Not sure if this is related.

What it looks like:
* Small horizontal tearing will start from near icons and icon text labels.  Looks almost like a HAM mode color bleeding.
* Several minutes later, white vertical bars, starting from the bottom of the screen will begin flickering in and out, while growing in height.  They're approx 10 px wide, and don't seem to corrupt video memory, and also don't affect hardware sprites, such as your mouse pointer.  At the worst case, I've seen these bars grow to be almost half the height of the display (200-300px high - width of bars never changes, though.)
* Condition temporarily worsens with heat
* Condition permanently worsens with age

I remember hearing of fixes for this, but never seen anyone actually fix the condition on a machine, so I can't speak to what needs to be done.  The first machine I had that displayed this problem I had repaired under C= warranty.  The repair was a new motherboard, though.  The replacement also started displaying problems, but by then, C= was gone.  

I currently own an A1200 with this problem, but since I only use it for games, and in NTSC mode, it rarely displays this problem, and even when it does, it's so minimal I don't care.

Hi!

Thanks for the information!

If I remember correctly, many Escom A1200-computers also had some problems (apart from the floppydrive  -  most likely the same). They reproduced
the old 1D-motherboard atleast in some point.

[PulsatingQuasar]

If I do these modifications to the my A1200, what will be the benefit of it.

More stable system? Faster?
What will it help!

Before I start modifying I would like to know what I can expect

[Skippy]

I've got the Rev 2b board, apparently the most bug'd.

I have the R152a and R118 fix I think there's a third fix somewhere...

Skip

[Damion]

Interesting, I have an Escom A1200; I believe the
motherboard revision is 1D4 (ntsc). To date I have had zero problems, neither with my old 8mb baseboard, the 1260 or the floppy drive.  Maybe these issues were resolved with certain revisions?