A cure for A1200 accelerator / expansion instability

[Photon]

I posted this just because it was long overdue since I did the 100 MHz Apollo-060 tests in my "A1700".

It was unbootable at 100 MHz, mainly due to a weak point between the accelerator chips and the memory. It's known that not all Apollos or Blizzard can go to 100 MHz but that 90 or 95 MHz usually works fine (with the appropriate 68060 chip version, of course).

But strangely, I continued to experience instability when going back to 80 MHz! This surprised me so much that I suspected the female connector. (Basically because re-inserting sometimes helped.) I perfected the socket and the instability remained in my A1200, on two motherboards.

Then, when I put the A1200 mobo in my A500 case, the symptom grew more pronounced, and I pushed here and there, reinserted, and still thought it was the female connector and that basically all hope was lost, I thought I just had to get a 'proper stable accelerator'.

-~-
But looking at the A500 case, I saw that the weak plastic bottom sagged between the rubber feet under it.
-~-

The same must be true for the A1200 case, but to a slightly smaller extent.

This of course meant that however flush I made the steel-plate bottom half of of the RF shield to the case, the case itself would sag and the expansion card would simply "hang" on the mobo male connector, and the mobo won't bend to follow, giving bad contact. And the female connector is so very tight that any change in temperature will cause the same problems as for any clip-onto-SMD-socket board for other Amigas: bad contact.


The solutions:

1) Remove sagging.

For my A1700, it was so extreme that it required a small plastic spacer under the board (to raise the right end of the board to make exactly horizontal like the mobo) and a plastic sheet as thick as the rubber feet under the case, to stop the case from sagging.

For A1200 owners, the solution could be to put the thinnest possible adhesive anti-skid sheet under the case, and/or sand down the rings around the rubber feet down and of course remove the rubber feet. Everything should in theory then be exactly horizontal.

Putting two or four rubber feet on the expansion lid could also work, but note that they won't be recessed like the normal ones. I think I'll go with the no-rubber-feet-at-all solution, if I have the oomph to fiddle some more.

2) Make everything level.

First, unscrew all screws holding the mobo to the case bottom and loosen the hex screws by each connector on the back so they won't lift the board off the case bottom. Now, the screws that don't go through holes in the mobo are okay, they just hold the RF shield bottom to the case bottom. But there are some screws through holes in the mobo, and these push the mobo into the plastic between mobo and RF shield until the solder points/component pins dig into that plastic.

Insert the accelerator straightly. The mobo will adjust itself in height to perhaps make it "hang" on the accelerator female connector. Not good. If so, tweak/bend the thin steel supports of the RF shield until you look carefully and the mobo and accelerator are level and horizontal.

Screw the mobo screws back in, but only allow them to just touch the mobo, or they will bend down the RF shield supports and make this unlevel again. Look out for non-thin patch wires on the underside of the mobo, this will lift up the board. Finally, just tighten the hex screws by the connectors without any force.

Now you know that the mobo is at the correct height and horizontal without lifting or pushing down the female connector of the accelerator.

-~-

I think this is the cause of many A1200 accelerator owners wrongly calling their accelerator unstable.

My A1700 has now been the fastest and most reliable Amiga I have, for a long time.


You might have a for real electronic problem with your accelerator, but 68060s never overheat, heat is not a problem for the accelerator chips either, and without static damage to chips or physical damage to board layers and traces, expansion cards are never but never unstable because of an electronic failure. Instability is almost always "bad contact" (as in corroded traces or failing solder points).

That means I can't promise that your card will work after this fix, but if re-inserting and "pushing at different points on the board" (or "works on my bench but not in the case", or the classic "lift front 2 cm and drop the case on the desktop" )has made it work for a while, THIS should be the cause of the instability and your card is OK.

[delshay]

There a few more things that make a stable A1200. This I have being working on for the past month. Test runs for a minimum 24HR.

Putting buggie software a side,it has not crashed or lock-up during long test runs.

With improved stability also comes new speed. One thing I can say and i 100% guarantee it, there's going to be a new world record for A1200

[Cymru]

With great speed comes great responsibility!

[roy bates]

this was pretty sound advice,yes its true any card wont like being at an angle on these type of connector keeping it flat and level with the motherboard is a very good idea.

it also helps when finding other problems.

[Photon]

Well, I should make it clear that how much the angle affects stability depends on how tight the female connector is. The ones I've tested have all been tighter than PCI or PCI Express slots in a PC or the A500 expansion connectors. The pins are springy like the PC/A500 ones, but the gap in the plastic is smaller, so that the spring pressure of the pins can't protrude much at all beyond the plastic. With each degree away from exactly level, the springy pins are sort of lifted off the upper pins of the mobo by the plastic (instead of the pins) touching the mobo pin edges. Since they protrude so little, some of the pins will exert very little pressure on the copper of the mobo pins -- or none at all.

At speeds around 20 MHz, poor contact quality starts to play in, and it's then that this causes instability.

The reason for loosening the hex screws by the connectors is also that there is another angle, the slope of the mobo from the connectors to the front. If this is not level, it will affect the contact quality even more. But unless you have put something under the mobo that pushes it up, or something under the expansion board (like chips preventing you from closing the expansion flap) that prevents it from lying flat on the case, it should be level. Even if the A1200 case is sagging, where the board is it doesn't sag more at the end of the mobo connector near the back connectors than the front, so the sag only affect the angle mentioned in the original post. But you could loosen everything and put the expansion card by the mobo connector and look (without inserting the card).

The goal is that when the card is inserted, no pressure should be applied to the card by the mobo, the card shouldn't "hang" on the connector, and there shouldn't be anything pushing up under the mobo or card to "warp" it. Then, when you fasten the screws, the same rule must apply. (Sadly, some expansions have chips or memory under them that makes this impossible. Then what you must do is put plastic spacers between RF shield and mobo that raise the mobo - so that when you just lay the card down next to the connector, the card lies flat and is in height with the mobo pins.)

[clauddio]

the big problem with some A1200 accels are that some of them have a buggy female connector with buggy bronze which oxidizes with the time causing serious problems and headdaches....specially apollo 040 and 060 boards have this problem
The best way to solve is cleaning the connector often and removing the oxide using alcohol or any good product

[Photon]

What, alcohol is not a good product!? Well, I think so.

Yep, all connectors oxidize except gold-plated ones. Any electro-cleaner that isn't lubricating (ie. wasn't made for cars or locks also) is fine, just spray on and insert and you're done.

[clauddio]

Originally Posted by Photon

What, alcohol is not a good product!? Well, I think so.

Yep, all connectors oxidize except gold-plated ones. Any electro-cleaner that isn't lubricating (ie. wasn't made for cars or locks also) is fine, just spray on and insert and you're done.

you are talking about the gold connectors as some soundblaster cards have?