PLCC SOCKETS ARE EVIL

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exxos
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PLCC SOCKETS ARE EVIL

Post by exxos » Tue Aug 22, 2017 10:11 pm

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While testing out a booster prototype I found that it refused to work with the 68HC000 CPU. I first thought that there was some problem with my PLD code. Later I had bypassed the PLD totally and hardwired the 68000 DIP socket to the PLCC socket. So my PCB was basically a DIP to PLCC adapter. Problem was, it just refused to work. Oddly though, a older TTL (IE original PLCC CPU) worked fine. To which point I blamed the 68HC000 CPU for being faulty.

Several CPU's later, and I couldn't figure it out. The motherboard and booster "adapter" worked fine with a TTL CPU. But adding in CMOS (HC) CPU refused to work. I decided to test those CPU's in my STE and they all worked fine. This made no sense at all. How could the CPUs test fine in my STE but not work in my simple adapter PCB ?!

I dug out a original V2 booster and it booted right up first time. With the HC CPU. So clearly the issue wasn't some compatibility issue with the CPU itself and the motherboard. I even tried a second motherboard and that behaved exactly the same. So the motherboard itself wasn't the problem. Just 2 motherboard refused to work with my HC CPU, but would work with the V2 booster which did use a HC CPU. Again, this made no sense.

So I took out the CPU from the V2 booster, it was known working setup of course, and put in another one of the HC CPU's I had been testing. The V2 booster did not boot up. I tried a few more CPU's.. booster wouldn't boot at all. At that point I tried the boosters original CPU (that worked) in my new V2 design and it did not boot, still.

I thought to go back to "square 1" and put back the known working CPU back into the original V2 booster to make sure I had not broke anything or had a bad connection. To my amazement, the booster refused to work! WTF is going on ?! I tried the original DIP CPU back in the motherboard and it booted right up. So clearly not a motherboard problem.

So now I had re-tested all the HC CPU's back in my STE and each one worked fine. So at this point I had assumed that I had managed to kill the V2 booster. Though that did not really add up since the boosters own CPU refused to work in a simple DIP to PLCC adapter. But wait it gets better! Placing the original TTL CPU into the V2 booster worked, and even worked in my DIP to PLCC adapter (which was the next gen V2 booster hacked that way). So clearly the CPU's were not faulty, The boosters were not faulty, but the CPU's refused to work in the boosters ?! The same CPU's had been used countless times for years in my booster projects! This all made no sense at all.

It was the weekend, I spend the weekends with my girlfriend where I ranted on about all this not making any sense. She suggested maybe the new CPU's are damaging the sockets somehow which would explain why the V2 booster, worked one moment, and refused to work after some CPU changes. Though this did not really make sense as to why the CPU's worked in the STE. But at least it was a new direction for me to think on.

As all my Atari stock was at her flat, I found out the old TTL 68000 CPU's and the newer HC CPU's as used in the STE boosters and said these are the CPU's they are identical. she looked at them and said they aint. Like, what ?! She noticed the HC CPU's pins were actually thinner and a slightly different shape! Odd I thought.. She also suggested again that maybe the new ones are damaging the sockets..

So I routed though some kits and dug out a socket from the blitter kit and let her look at those. I also thought, well, those CPU's work in the STE boosters, so I took a socket out of one of those kits as well. She looked at both sockets and both CPUs and noticed the HC CPU fits in one socket but not another. But the old CPU actually fit in both sockets.. like, WTF ?!

The sockets were slightly different. One socket had pins which were more '\' shaped. The other socket pins were more bent, like 'Y' shaped, well, half the 'Y' shape that is. Basically not a straight pin. I thought the "slanted" pins would contact better if the CPU pins were bent. Though maybe it was the CPU pins on the newer HC CPU being thinner which for some reason did not like one particular socket, basically the slanted pin ones. Though this did not really make sense either.

She later found that the older CPU's fit fine in both sockets, but the newer CPU was a really tight fit in one socket, but not the other one. I looked into this and what I found next actually shocked me.

The HC CPU while it had thinner pins on the bottom, I would assume it was done to aid in SMT manufacturing. So the slated pin sockets would be contacting at a angle more on the bottom of the CPU pins. Which would make it seem a bit suspect if it would contact properly or not. Though oddly that wasn't the issue.. it gets better...

The HC CPU pins on the side are actually WIDER than the original CPU, so the contact area should be better on the 'Y' shaped pins. Though this did not fully explain things either..

I looked at my website at my guide to removing the STE CPU socked and found they were also the 'Y' type pins (or bent pins as I am just going to call them). So this was painting a picture that those slanted pin types are causing some problems. It would make sense since the older TTL types had wider pins and the bottom than the HC types and would contact better. So I thought I had finally found the problem.. only it wasn't actually that either.. and it gets better still...

The slated pin sockets have tiny plastic "spacers" between the pins. I assume just to keep them in position. What I never realised until today, is that those plastic parts actually slot in between the gaps on the CPU pins themselves. This doesn't sound like a big deal but it was actually...

The slanted pin sockets, the plastic spacers (as I call them) being thicker, and the HC CPU pins being wider (at the top) actually resulted in the plastic parts of the socket, pushing the pins inwards to the point where the CPU's would no longer make contact in the other PLCC sockets. Oddly the older TTL types had wider space at the top, so it would never matter for those, which is what I found.

At some point in all this, I found also that once a HC CPU was tried in a slanted pin socket, not only did the socket bend the CPU pins out of shape, but it also distorted the plastic spacers and did at some point cause the original TTL CPU's not to work either. At that point I thought I had killed my V2 booster or motherboard by placing a faulty CPU in it. but it just wasn't so. So now we have the answer to all this chaos!

The original CPU's (TTL type, or even GLUE, MMU chip etc) will work in either type of socket without problem. BUT, the HC CPU's will ONLY work in the 'Y' shaped (bent pin) type of sockets. If you try and place a HC CPU into the '\' shaped (slanted) pin sockets, it will damage the socket AND damage the CPU pins.

The slight "red herring" in all of this was all the CPU's worked in the original Atari PLCC sockets even though the CPU pins were actually bent and wouldn't work in any other socket! So lesson learned that newer sockets are not better than the ones in the 80s.

I guess its also annoying that now any sockets I buy, I have to really check they are the bent pin types before using them in any booster projects. Of course such sockets do not matter with older chips.

I think also there is some split blame here. I can blame the slanted pin sockets for bending the CPU pins, Or I can blame the HC CPU's for damaging the sockets! Or maybe this is just down to tolerances. Maybe the sockets are on the max tolerance along with the CPU. Just so happens that "both" of them being on tolerance extremes that they can actually damage each other. Madness!

Either way, I now know that all PLCC IC's have differences along with the PLCC sockets. The difference are so tiny at a first glance they would go un-noticed. Though I had to post about this as this drove me nuts for 2 days. Hard lesson learned... Never assume anything is as you think it is, and even a innocent PLCC socket can have tiny differences that can stop something from working and test your sanity..

Here are the images.. (click for larger image)
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TOP IC - OLD TTL CPU
BOTTOM IC - NEW HC CPU


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LEFT - OLD TTL CPU
RIGHT - NEW HC CPU


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LEFT - OLD TTL CPU
RIGHT - NEW HC CPU


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SLANTED '\' TYPE CONTACTS


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BENT 'Y' TYPE CONTACTS


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SPACER THICKNESS VARIATIONS

So lesson learned. Not all CPU's are the same size and shape, and neither are PLCC sockets!


..wrap..
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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Re: PLCC SOCKETS ARE EVIL

Post by exxos » Tue Dec 05, 2017 1:27 pm

Another update..

These new sockets I got have the "Y" shaped pins but I believe the plastic spaces which are supposed to sit in between the pins are too large on these sockets. So it is resulting in the plastic pushing away the CPU pins away from the socket pins..

I apologise for the blurriness of the images, but I am simply unable to get the pins the spaces in focus at the same time..

With this example the 68000 CPU.. The plastic spaces seem to flush up against the plastic body of the CPU itself..

The angle of the camera makes it look like the plastic spaces or running out, but they are actually not..

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With this second image you can see a lot better that the plastic spaces seem to be resting on top of the CPU pins..

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A close-up of these sockets...

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And the problem I had before was these plastic spaces were too wide.. And these sockets also look to wide.. The sockets I found which worked before had a very long and thin spacer with "Y" shaped pins. So actually assumed that good sockets were with "Y" shaped pins. Obviously this assumption has now gone out of the window :roll:

From my images above I can see the good socket I was using had "ITT CAUTION" by the looks of it. But my new sockets which I was sure I got from the same supplier last time.. Obviously these sockets are different again :roll:

So I am now on the hunt for good sockets again :roll: I will have a very good look at datasheets and trying find out if I can find the "ITT" socket brand as well. I may just buy one socket of everything that Farnell sell and just try every single one ...

... To be Continued...
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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Re: PLCC SOCKETS ARE EVIL

Post by exxos » Tue Dec 05, 2017 2:10 pm

These sockets look like the ones I have...

http://uk.farnell.com/3m/8468-11b1-rk-t ... dp/1183031
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Assuming that the image is correct...

The only other one stock look like the spaces are too wide as well...

http://uk.farnell.com/multicomp/mc-68pl ... dp/2097216

:roll:
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Re: PLCC SOCKETS ARE EVIL

Post by IngoQ » Tue Dec 05, 2017 2:21 pm

Maybe have a look at these:

http://www.precidip.com/en/Products/PGA ... 4-008.html

Everything I had seen so far from them is very good quality, swiss-made. You can check a CAD drawing online, if it fits your needs.

I bought mine at RS-Online.
Ingo :geek:

“Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away.” - Antoine de Saint-Exupéry

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Re: PLCC SOCKETS ARE EVIL

Post by exxos » Tue Dec 05, 2017 2:29 pm

IngoQ wrote:
Tue Dec 05, 2017 2:21 pm
Maybe have a look at these:

http://www.precidip.com/en/Products/PGA ... 4-008.html

Everything I had seen so far from them is very good quality, swiss-made. You can check a CAD drawing online, if it fits your needs.

I bought mine at RS-Online.
That's a pretty nifty site... Looking at the 3-D drawing, it still looks like sockets I have now. I will have a look through Mouser next and see if I can find some other brands..

I'm really thinking of just avoiding these sockets altogether in future. They seem to be a lot more trouble than they are worth.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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Smonson
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Re: PLCC SOCKETS ARE EVIL

Post by Smonson » Tue Dec 05, 2017 10:56 pm

Your girlfriend is very wise. Can she take a look at some of my projects for me?

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Re: PLCC SOCKETS ARE EVIL

Post by rpineau » Wed Dec 06, 2017 2:40 am

The only one available from mouser is the Preci-dip one... there is probably a reason for this.
The one from Farnell are 3M .. 3M is supposed to be a good brand too.
It's really weird to see that many issues with these sockets but from your pictures it's clear that the plastic part is going too far in and could prevent the pin to make proper contact.

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Re: PLCC SOCKETS ARE EVIL

Post by exxos » Wed Dec 06, 2017 9:16 am

rpineau wrote:
Wed Dec 06, 2017 2:40 am
The only one available from mouser is the Preci-dip one... there is probably a reason for this.
The one from Farnell are 3M .. 3M is supposed to be a good brand too.
It's really weird to see that many issues with these sockets but from your pictures it's clear that the plastic part is going too far in and could prevent the pin to make proper contact.
Other way around ;) The plastic part should go far in , thats a "good" socket. The spacers can't fit between the IC legs, so the spacers push the legs inwards on the CPU itself, and away from the metal contacts on the socket.

The sockets still seem to be generally ok, but I still not happy with it. I cannot find any other sockets than 3M or preci. So likely on production boards, I will just have to forget sockets and solder the CPU direct to the PCB.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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Re: PLCC SOCKETS ARE EVIL

Post by grobda » Wed Dec 06, 2017 2:03 pm

Had a similar issue when fitting a blitter to a STFM with a PLCC socket salvaged from a dead motherboard. Chip was loose in the socket. Managed to get it working by pushing some fine pin strips between the socket and the chip. Not an ideal solution but less hassle than desoldering.

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Re: PLCC SOCKETS ARE EVIL

Post by exxos » Wed Dec 27, 2017 10:26 pm

IngoQ wrote:
Tue Dec 05, 2017 2:21 pm
Maybe have a look at these:

http://www.precidip.com/en/Products/PGA ... 4-008.html

Everything I had seen so far from them is very good quality, swiss-made. You can check a CAD drawing online, if it fits your needs.

I bought mine at RS-Online.
These sockets look like the last resort, the Dimensions I cannot really find :( does not really seem to be a proper technical drawing.. I will order some from RS tomorrow and just see if they will fit the CPU or not..

If these sockets do not work either, then I will just have to to forget using them all together with these newer CPUs.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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