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Amiga 1200: Timing Fixes

I've recently been trying to get a PCMCIA wireless card going in the Amiga 1200 and have had no luck. Every time I try to initialise the card, the entire machine locks up. You can't even move the mouse pointer.

Initially, I thought it was drawing too much current from the ageing power supply. To remedy this, I purchased an ATX power supply and wired it in (I'll post an article on this shortly.) Unfortunately, this wasn't the solution.

After a lot more googling, it seems that my A1200 might have the dreaded 'timing issues' that are mentioned across the web. It seems that, during construction of these machines many decades ago, some were fitted with capacitors and resistors that weren't meant to be in the final design. The motherboards actually have the spaces for all of these components, so I can imagine it would be easy for an employee on the construction line to accidentally insert components that were part of a draft design and not meant for the final.

Note that a system without acceleration will (most often) not realise any of these timing issues. The symptoms really only appear once you start pushing the hardware.

Timing Issue Symptoms

There's a really good forum post here that details a lot of motherboard/accelerator combinations and the successes/failures that people experienced. In the end, the result is a total crap-shoot! It seems total luck-of-the-draw as to whether your accelerator will work with your motherboard.

Timing Issue Solution

Fortuantely, you shouldn't despair just yet. There are known solutions for all revisions of the Amiga 1200 motherboards and I'll list (and attempt) two of them below.

Your solution will depend entirely on what accelerator you have and what motherboard revision it's plugged in to. There are two basic groups of accelerators (ACA and Apollo) and instructions for both methods involve removing/adding SMD components. These tiny little resistors and capacitors are an absolute nightmare to deal with and will require a good soldering iron and a VERY steady hand.

Searching around the web, it seems that everyone has their own theory as to what solution is best for what accelerator. It was actually quite hard to draw a concise picture as to what was required for my ACA1220.

For both Apollo and ACA, Ian Stedman has a great wealth of knowledge here which includes the required fixes for both.

ACA themselves also have instructions on timing issue fixes. They only seem to mention the removal of items though. Reading other forum posts, it seems that this is only 'half the job' for a proper timing fix.

There's also a summary of the ACA fix in this thread. I'll quote the information here to make sure it doesn't go missing:

FOL 16:54 01 January 2013
To help others, this is the full fix that should be applied.

E121R and E122R need to be changed to 60ohm Ferrite Beads.
E121C and E122C need to be added (22pf), if not already.

Only E125C should be removed (insome cases you need to leave it). E125R, E125C E123C and E123R should be present.

Some rare cases, you need to leave E125C on and remove E123C.

Note that the ferrite beads mentioned above are 100ohm? But the ones on Ian's page are 60ohm?
Also, note that on the second-last line, I've changed it to what I believe is the correct component reference. It initially indicated that 125C should be removed, but then says that it might be needed... then that it should be present. I believe that the final three items listed should be E125R, E123C and E123R. Not 125. (Actually, if you read the entire forum post, you'll see that FOL corrects the error as I have above.)

It's minor differences like this that can be REALLY confusing.

Following ACA's Recommendations

The rules are meant to be simple: remove four capacitors. Well, turns out these are tiny SMD components and the removal wasn't as trivial as I had hoped. Make sure you have the time and space to focus.

Removing SMD capacitors requires you to heat up the entire item and lift it in one go. Do not try to heat one side and then the other. I used a pair of tweezers, grabbed the capacitor in the middle and then placed the soldering iron through the tweezer grip. The goal was to make sure that the soldering iron would touch both sides that needed to be melted; adding a little bit of solder to the tip of the soldering iron helped as well. Once hot enough, you can then lift the entire lot and the capacitor should be freed.

I actually had the whole SMD component lift with the soldering iron and stick to the tip most times. This probably damages them entirely, but I had a new set of components to put in place, so there was no harm.

After removing all four capacitors... I tested the PCMCIA card and it still locked up! Boo hoo... What to do next? FOL's next advice is as follows:

FOL 15:27 01 July 2013

Originally Posted by marcel21674:
ok, opened up my 1200 this morning. Just to prepare, for some upgrades the next couple of days.
After removing the RF-shield, i thought of removing the E123C and E125C capacitors, but surprise surprise, the already have been removed....
So my rev.2B motherboard does have some timing fixes, but it didn't fix the issues with the aca1232...

Pretend it doesn't.

Add All four components, then do fixes as if your doing it for the first time.

Change E121R and E122R to 60ohm Ferrite Beads,
Add E121C and E122C 22pf caps.
Remove E125C, test A1200. If its all fine, leave it.
If E125C doesn't help, then readd E125C and remove E123C and test again.

I your still having trouble, then try removing both E123C and E125C, then test again.

The forum thread ends with the original poster indicating that they'll try the fixes. Of course... no resolution is mentioned... I might sign up and ask how it all panned out. I'll also try the fixes myself.

The best part about the fixes is that, despite a few minor capacitor values (22pf vs 27pf), the instructions map directly to Ian Stedman's directions.

Following Ian Stedman's Directions

Ian's page indicates that the following changes are required for all Amiga 1200 motherboard versions when using accelerators manufactured by ACA. I've added links to the relevant components at Element 14.

E123C E125C E123R E125R E121R E122R E121C E122C R118
Try fitting 22pF SMD Capacitor if it does not work Fit 22pF SMD Capacitor Fit 27ohm SMD Resistor Fit 27ohm SMD Resistor Change to 0.1ohm Ferrite Bead Change to 0.1ohm Ferrite Bead Add 27pF SMD Capacitor Add 27pF SMD Capacitor Leave alone

Once your care package has arrived, you can prepare your motherboard for surgery. Do be careful extracting the motherboard from the casing. Make sure you unplug every component and unfasten every screw. Excessive force is NOT required.

DSC05071 DSC05072 DSC05078

The components are absolutely tiny and come in ribbons. The plastic sheet can be peeled back, allowing the components to pop out.

DSC05062 DSC05065 DSC05066

Fitting all the components is a nightmare... but I managed to do it with my crappy soldering station.

DSC05075 DSC05076 DSC05081

That's the ferrite cores... installing them was just as hard. I found that soldering one side, then the other and finally returning to the initial side worked ok. The issue would be that it was easy to solder them in at a bad angle and then re-touching meant throwing the components completely out of alignment.

All changes were made... but the PCMCIA card still played up. Turns out the timing issues aren't my main concern.

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About stevenh

Trains… trains… trains… + Electronics + Japan.

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