A1200 motherboard timing issues

[ant512]

Originally Posted by DrBong

You can find drivers for the Blizzard 1260 and more at the Big Book of Amiga Hardware website.

I nearly posted a link to those, but wizard66 is actually looking for the GVP 1260 drivers.

[JuvUK]

2B board here with Apollo 060 all fine and dandy (no timing fixes) wierd huh?

[Enverex]

Originally Posted by oldpx

The thread might not be TOO old but I must remind that the original poster isn't visiting eab anymore. Yet there is good information here guys

*cough* Since when?

[prowler]

Originally Posted by Enverex

*cough* Since when?

It's oldpx who doesn't visit these forums any more. I think that effort was just his parting shot.

Seriously, though, the whole question of A1200 motherboard timing issues was explained by Eyetech in this document:
http://web.archive.org/web/200010150...0/AMIGA001.HTM

They sent me a copy of it when I bought an Amiga OS 2.1 disk set from them.

[AlfaRomeo]

Originally Posted by wizard66

How to do ?


*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, i.e. the Alice chip

How can we differentiate REV -01 from REV -02?
I have a mobo REV 1D4 but don´t say if it is REV -01 or REV -02

[Bamiga2002]

You just do as you're told here. With revision 1D4 just remove capacitors E123C & E125C.

[Andymiga]

Originally Posted by Bamiga2002

You just do as you're told here. With revision 1D4 just remove capacitors E123C & E125C.

I'm intending to do this mod for my 1D4 board, too.
Thanks for that link, the instructions are very clear.

However, there's an ambiguity with the instructions behind that link.
In the text, it says that the capacitors E123C and E125C should be removed.

BUT in the picture, the resistor(?) E123R and capacitor E125C are marked!

Soooooooo.... should I remove E123R or E123C ? I guess it is only the 'C' components that should be removed, but I'm checking here to be 100% sure.

Thanks

[AlfaRomeo]

Just when I would remove the capacitors E123C & E125C from my 1D4 mobo I saw that E125R, E125C, E123R & E123C were not soldered on the mobo.
What that means?.. In this case there are no fixings to made or there are another fixings otherwise E123C & E125C?
It is possible that are mobo´s 1D4 with timing fixings from factory?

[Bamiga2002]

Originally Posted by Andymiga

However, there's an ambiguity with the instructions behind that link. In the text, it says that the capacitors E123C and E125C should be removed.

BUT in the picture, the resistor(?) E123R and capacitor E125C are marked!

Now you got me confused too . I removed the ones that are marked E123R and E125C like the picture suggested. Can someone confirm that's the right way?

[AlfaRomeo]

Originally Posted by Bamiga2002

I removed the ones that are marked E123R and E125C like the picture suggested

As much as I can understand the components to remove are only the capacitors (E123C & E125C)

[rkauer]

Only the capacitors! don't mess with the resistors or the Amiga will not boot anymore, until you replace them.

[Andymiga]

Originally Posted by rkauer

Only the capacitors! don't mess with the resistors or the Amiga will not boot anymore, until you replace them.

Okay, so we only remove the capacitors that are marked E123C and E125C just as (all) the instructions tell us.

And the picture on that webpage is *wrong*:
http://www.ianstedman.co.uk/Amiga/am..._mobo_fix.html

Thanks, Merry Christmas Mr. Amiga

[Bamiga2002]

It's a few years since i removed the thingies from the mobo (so i might remember wrong!). I must double check which ones we're removed. Well, it's booting and working ok so i must have removed the right ones .

[Zetr0]

Originally Posted by JuvUK

2B board here with Apollo 060 all fine and dandy (no timing fixes) wierd huh?

Beware this Thread Necromancer!!!!


*ahem, well found m8y

for all those interested in performing their own little hackery Stedy has indeed got all the info on his site.

Have a lookie here its not to difficult in truth, as long as you are not an absolute novice with a soldering iron.

as with all things, dont rush in, always check what you are doing with someone, or you may need a new motherboard.

[Andymiga]

Originally Posted by Zetr0

Have a lookie here its not to difficult in truth, as long as you are not an absolute novice with a soldering iron.

as with all things, dont rush in, always check what you are doing with someone, or you may need a new motherboard.

Yes thanks Zetr0, we are indeed checking to be sure --- because that page has contradictions (the picture behind that link has E123R and E125C marked to be removed)!

[NovaCoder]

Originally Posted by AlfaRomeo

How can we differentiate REV -01 from REV -02?

Yes, a very good question....anyone got the answer?

Budgie Rev 01
Budgie Rev 02

The Big Book of HW seems to be saying that the Budgie Rev -02 Release had the XR358 470Ohm resistor removed and an 470Ohm resistor added to pin 43 of Alice. So if you don't have that mod, it must be a Budgie Rev 01?

So in summary, if you've got an ID4 and nobody has performed the mods then you've got a MB with timing issues, even if they don't make themselves 'felt' with your particular setup?

If all ID4's suffer this 'issue', why were ID4's rated as the favourite MB on EAB, that's just crazy talk?

I currently have 2 ID4's, one looks like it's had some work on it done. Although one of them works fine with my 030, the other one won't even boot with it in

[Stedy]

Hi,

I will make a minor update to the A1200 timing fix webpage over christmas to clarify the removal of resistors and capacitors. Taking the opportunity, here is the relevant section of the A1200 schematic concerning E123 and E125.



You can see that E123R/E123C do not connect to any devices to the right of the resistor, denoted by the NC text. The same is true for E125R/E125C. The 7MHz clock and CDAC only connect from Alice (U2) to Budgie. So removing either the resistor or the capacitor will break the AC terminator.

This circuit is an AC terminator. It has a time constant of 1.30ns and was designed to remove high frequency components in the signal rise/fall time. Unfortunately the 22pF capacitor adds loading to the 7MHZ and CDAC lines which coupled with the input capacitance of Budgie (10pF?) + PCB trace of maybe 5pF, it increases the signal rise/fall times. The rise or fall time of a signal T = 2.2RC, where T is the rise time in seconds, R = output driver resistance, C = capacitance.

Most Commodore ASIC have a 4mA drive capability, which from spending too much time around IBIS/Spice models is approximately a 150 ohm output drive impedance
Plugging in the numbers, T = 2.2 x 150 x 37E-12.
T= 12.2ns

If we remove the 22pF capacitor, either by removing it or the resistor, the capacitive load drops from 37pF to 15pF. The rise/fall time is thus:
T = 2.2 x 150 x 13E-12

T= 4.95ns

Accelerator cards with logic buffers have a 3-7ns propagation delay added on. This helps to explain why some accelerator cards work better than others. I would need to re-read the A1200 CPU slot design notes to explain this further.

All formulas and rationale of driver output impedance derivation came from High Speed Digital Design, A handbook of Black Magic by Howard Johnson, chapter 1.

In summary,

Removing either E123 R/C or E125 R/C will perform the timing fix and allow your A1200 to work.

I modified my A1200 (Rev 2B) many years ago and my Apollo 1240 works fine, before I undertook the modification, it did not work at all with the Rev 2B board and the rev 1D4 board I had intermittent issues.

Ian

[TheCorfiot]

@Stedy

What can I say, Thank you ever so much my friend.

I believe that's cleared that one up for good...

Merry Christmas
TC

[Andymiga]

Originally Posted by AlfaRomeo

How can we differentiate REV -01 from REV -02?
I have a mobo REV 1D4 but don´t say if it is REV -01 or REV -02

Originally Posted by NovaCoder

Yes, a very good question....anyone got the answer?

Budgie Rev 01
Budgie Rev 02

The Big Book of HW seems to be saying that the Budgie Rev -02 Release had the XR358 470Ohm resistor removed and an 470Ohm resistor added to pin 43 of Alice. So if you don't have that mod, it must be a Budgie Rev 01?

Here's a good explanation on how to tell if your Budgie chip is 01 or 02:
http://haigh.net/Apollo_crashing.htm

Merry Xmas

[AlfaRomeo]

Originally Posted by Andymiga

Here's a good explanation on how to tell if your Budgie chip is 01 or 02:
http://haigh.net/Apollo_crashing.htm

Merry Xmas

Thanks Andymiga this site will help a lot