STE V1.5 32MHz BOOSTER - STATUS

Help & information about the STE V1 series boosters.
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Re: STE V1.5 32MHz BOOSTER - STATUS

Post by exxos » Fri Jul 13, 2018 5:51 pm

I took out the GAL and all the resistors and basically hardwired the CPU in as a stock setup, and it still does not work..

So I am back to thinking this is sort of bad connection fault again.. Though I do not like getting into these "going around in circles" problems. I guess it is possible these PCBs are simply rubbish..

I got my regular PCB guy to manufacture the final boards anyway. So of course I will do a lot of testing with those. Likely I will have 2 machines running, one with a 40MHz OSC, and another with a 32MHz OSC. And see if the 40MHz one dies or not.

I am still investigating, this seems a bit of a mystery :roll:

IMG_3042.JPG
IMG_3042.JPG (114.71 KiB) Viewed 1130 times

EDIT:

Checked bottom of the motherboard to the top of the booster CPU, all connections are fine. So there is nothing other than the CPU in circuit, direct connection as "normal" just doesn't work.

I took the CPU off the booster , back in the MB... works again.. So I will try a new CPU on the booster board.. This really doesn't make any sense...

EDIT2:

OK So I plugged the booster board directly ontop of the CPU in the MB socket.. now it doesn't boot.. hmmm.. there are no shorts on the board from what I can see.. even if there was, doesn't explain 10+ hours before it failed...

EDIT3:

OK so short on PCB between DTACK and BG , must have happened during my last re-solder.. So back on with the CPU again...and.. still doesn't work.. bizzare..

EDIT4:

Tried the suspect CPU in my old V1 booster (32mhz) and CPU came right on.. so can't be the CPU... all connections on the new booster board seem fine.. so what else is there ??

EDIT5:

Put a new CPU on the problem booster board and now it boots! So why does that one CPU work in the MB, work in the V1 booster, but died on the new booster boards.. Even though at the moment its hardwired for 8MHz.. No bad connections, no shorts, just refuse to work..


EDIT6:

So back to working at 40MHz now.. well bit unstable as not got the sil arrays in yet.. and its died again... :pullhair:


EDIT7:

Tried a previous revision board and hardwired that to 8mhz and seems to exhibit the same "fault".

I really think there is something bad on these test boards.. but I don't know what.. Will just have to wait until I get my proper boards and do more tests on those..

EDIT8:

So I found a short on the CPU :roll: So now its running at 40MHz again (though with a different CPU than originally). Though it still doesn't explain why it died earlier when the CPU tested fine in another board.

Think I am just going to put this down to its solar eclipse & Friday 13th.. Good enough explanation as any other...
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Re: STE V1.5 32MHz BOOSTER - STATUS

Post by exxos » Sun Jul 15, 2018 9:53 pm

Had a thought to check the CPU I was having issues under my microscope.. And look what I found..

Capture.JPG
Capture.JPG (158 KiB) Viewed 1075 times

Basically two pins have not had any solder on them. I don't know why as each pad on the PCB had paste, and I even checked under a magnifier that each pin was sitting in paste.. But the some reason paste did not adhere to the 2 CPU pins, even despite three or four re-solders. This also explains why it worked fine with a totally different CPU (I did not even re-apply any paste on this, just heat gunned the new CPU, so it was not a issue of not enough paste on the PCB).

As to why this worked for several hours without problems then suddenly died, and even past continuity checks is bit odd. Probably there was a few ohms resistance which made it seem okay with my meter, but when running at some MHZ , likely the resistance basically became open circuit. Basically similar kind of issues with bad contacts in PLCC sockets which I saw a lot of also.

So what I will do in future is leave the CPUs soaking in some IPA before I solder them, and of course never assume that CPUs are clean, even on "new" reels. I guess age could be a factor here.. But there does not seem to be any tarnishing on the pins and they look clean. The pins are straight and aligned with the ones next to it. So just something seriously odd where the solder simply would not stick to the two pins :roll:
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Re: STE V1.5 32MHz BOOSTER - STATUS

Post by PhilC » Sun Jul 15, 2018 10:26 pm

Well spotted.

Not sure why it would happen but can only assume oxydisation on the pin over the years, not that we can see it on the photo.

Could it be that the cpu and pcb flexed under the sudden application of heat? Reading the instructions on the paste I use talks about raising the temperature in a set procedure.... Not that I ever do? Maybe it would solder better in an oven? Just put it under the pizza not on top.
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Re: STE V1.5 32MHz BOOSTER - STATUS

Post by exxos » Sun Jul 15, 2018 10:30 pm

Forgottenmyname wrote:
Sun Jul 15, 2018 10:26 pm
Not sure why it would happen but can only assume oxydisation on the pin over the years, not that we can see it on the photo.

Does not appear to be any tarnishing or oxidisation from what I can see.
Forgottenmyname wrote:
Sun Jul 15, 2018 10:26 pm
Could it be that the cpu and pcb flexed under the sudden application of heat? Reading the instructions on the paste I use talks about raising the temperature in a set procedure....
It was soldered in a oven originally.. Of course bad joints can happen if the PCB and the solder melts and the CPU pin isn't up to temperature and it does not stick.. But the whole thing is heated up equally so that should not happen.. Even so, I heat gunned this board taking the CPU off and on, and the pins resisted the re-soldering each time.. And I even plastered lots of flux over everything each time. So it's not soldering this amount of times is nearly impossible.. The only thing it could be as if the pins were bent such a way solder did not touch the pins.. But all the pins seem level to me..
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Re: STE V1.5 32MHz BOOSTER - STATUS

Post by exxos » Mon Jul 16, 2018 11:47 am

So the current booster was running a couple of hours then died again :roll: I fluxed the board up and re-heated twice and it made no difference. The third time I heated it up , and pushed down on the CPU for a couple of minutes until it had cooled, and now it works!

So what I am going to do is see if I can get a thicker stencil made to get more solder on the pins. I will also see if I can paste up the pins directly on the CPU and get some solder on them before actually soldering it to the PCB. At least that way I can make sure solder is adhering to the CPU pins before actually soldering it to the PCB.

.. And here's me thinking that PLCC sockets were evil and the pain ass... :lol: :roll:
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Re: STE V1.5 32MHz BOOSTER - STATUS

Post by exxos » Mon Jul 16, 2018 1:12 pm

What I will try today is pre-soldering the CPU pins on the PCB as shown below.. Then I will paste the whole board and assemble.. This way the CPU pins have double the amount of solder on them..

pre-paste.jpg
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Re: STE V1.5 32MHz BOOSTER - STATUS

Post by troed » Mon Jul 16, 2018 1:43 pm

(The next update will be from Chris swearing over hard to find connections between pins ;))

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Re: STE V1.5 32MHz BOOSTER - STATUS

Post by exxos » Mon Jul 16, 2018 1:44 pm

troed wrote:
Mon Jul 16, 2018 1:43 pm
(The next update will be from Chris swearing over hard to find connections between pins ;))
Most probably 8-)
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Re: STE V1.5 32MHz BOOSTER - STATUS

Post by exxos » Mon Jul 16, 2018 4:37 pm

Board is getting there :)

I just tested the 8MHz switch and while it works, it actually glitches during transition :roll: I think it is a problem with my wait state code.. So currently sidetracked while I investigate the issue...

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Re: STE V1.5 32MHz BOOSTER - STATUS

Post by exxos » Mon Jul 16, 2018 5:51 pm

It does not look like a real-time 8MHz switch will be possible with this design. There simply isn't enough IO power in that PLD :(

Problem is I have to delay DTACK because the CPU is running faster. Though I also have to turn this delay off to get back to stock 8MHz speeds. The problem is when the switch happens the DTACK delay time basically becomes random and causes issues.

The fix would be to have some logic to allow the 8MHz mode wire synchronised to DTACK so the switch only happens when there is no bus activity at all. Unfortunately this simple GAL simply does not have enough logic elements to implement that code. It wouldn't be a problem with a second GAL, but I don't think it's really worth designing another add-on circuit just to do real-time switching. Frankly there are more important to be working on than that.

So while the booster will be switchable between 40MHz & stock 8MHz, it will likely cause a crash if switching with the power on.

EDIT:
I may make a quick GAL test and just upload the info here, so if anyone wants to adapt it design a small addon PCB, then they can add it themselves..

EDIT2:
OK my brain has gone to sleep..

Anyone think how to allow a single to only propagate when signal is HI ?

Logic would be regardless if SW (8MHz switch) is high or low, it will only allow signal to propagate when DTACK is HI..

I guess a clocked flip-flop would work if the clock input enable was based on DTACK.

EDIT3:
Seemed to have made some progress bodging the GAL code in getting the clock switching to work...
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