Excelerator plus pcb repair warning

Disk drives, Monitors, SuperCPU etc.
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Gyro Gearloose
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Excelerator plus pcb repair warning

Post by Gyro Gearloose »

The PCB is poorly designed, the traces are far too thin for no reason and the capture pads are far too small for no reason and there is no tear-dropping to get the too-small traces nicely into the too-small capture pads and the substrate is fragile. :x

Expect damage even with careful desoldering. I recommend simply snipping off the broken IC, adding fresh solder to each pin on the bottom with a temperature controlled iron set to 650F or as low as possible to flow solder. Add some flux, this is to let the desoldering iron have a good thermal contact. I used a Hakko desoldering iron and even with that I managed to break two pads open. What a POS board.

I snipped the IC off because even though it's a two layer board, some pins are connected to large copper areas and it was tough to desolder. Removing the IC reduced the heat sinking. Maybe if you start right away by adding more solder and flux you can skip the snipping part.

Also don't expect the soldermask to hold up like a modern one, it's a thick old lacquer-type and damages quickly.

This drive is whackadoodle. I hope it works soon or else I am very tempted to toss it under a steam roller with an Atari logo on it.


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Gyro Gearloose
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Re: Excelerator plus pcb repair warning

Post by Gyro Gearloose »

The funny thing is the drive is built with a mezzanine board, a daughterboard that plugs into the main board.
That board is designed correctly with wider traces and much larger capture pads.
This board would be a lot easier to remove a chip from.
good pcb
good pcb
The main PCB is so fragile. I mean I never mangled a C64 mainboard, so it's not like 1980s PCBs would be that hard to work with. I've worked on 1967 PCBs and those are easy to damage but even they don't lose copper pads...
crap pcb
crap pcb
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Gyro Gearloose
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Re: Excelerator plus pcb repair warning

Post by Gyro Gearloose »

I repaired the broken traces with some 30 gauge solid conductor teflon coated good stuff:
Image
Image

Now the drive powers up and the motor stops spinning after about 5 seconds. This is normal behavior I guess. I'm calling off the Atari steamroller.
Given the amount of trouble I think it would have been better to try to solder a wire to the old chip's nub. I'd have saved a bunch of copper pads...
I'm pretty glad I found a 74LS133 DIP here in Montreal. It was the only 74 family chip I didn't have in my crap.

What bothers me now is the fact that the two EPROMs (not sure what's on them yet) touch the metal case. This is not great.
Image

Given that I think my desoldering skills suck (ha ha! a pun! get it?) these days I will leave those sockets there and maybe replace the fat ceramic chips with some EEPROMs. I wonder if a 28C64 will fit...

Oooh and check out my 5v/12v power supply. I used one of my little TO-3 5V switchers I made and powered it with my lab power supply. 12V goes to the drive and the switcher, 5V to the drive.

Image
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Re: Excelerator plus pcb repair warning

Post by Gyro Gearloose »

I cleaned my desoldering gun to make sure it sucks well, I changed the tip to a 0.8mm instead of 1mm, I put fresh solder on the pins of the chip I wanted to remove, kept the temperature of the tip close to 650-700F (my gun is so old it doesn't have a temperature readout, I simply go by how fast it melts solder and that the tip doesn't turn black and blue from overheating)
... and while it went better I still managed to break one trace and pull out three via barrels from the 2kx8 chip... :(
and it tested OK on my tester.
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Re: Excelerator plus pcb repair warning

Post by radron5809 »

Would something like ChipQuik help in this situation. Never used the stuff but saw iphone repair using it, add some to solder joint and brings down melting temp so you can desolder without as much heat
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Re: Excelerator plus pcb repair warning

Post by Gyro Gearloose »

I believe that ChipQuik is used more for surface mount parts. A through-hole part has solder on both sides of the board and inside the via barrel. To get the ChipQuik to mix in with all that solder to bring the melting point down is not possible I think. You have to melt the old solder first anyway. The ChipQuik is used so that all those surface mount pins stay loose long enough to heat them all up with an iron. I'd use hot air for that.

https://www.chipquik.com/store/index.php?cPath=200

I really think the PCB is the problem here.
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Re: Excelerator plus pcb repair warning

Post by Gyro Gearloose »

Something just occurred to me; that daughterboard looks hand drawn, those pads look just like the dry transfer decals they used to sell at Radio Shack.
The main PCB could have been designed by an entirely different team using CAD, but didn't quite set the parameters right.
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Re: Excelerator plus pcb repair warning

Post by Gyro Gearloose »

Image

LOL that brings back memories. Check out the DIP patterns with the fat pads, those rounded rectangles. Betcha that daughterboard was drawn on a light table.

This is how it was done without computers. Oddly there was already automated PCB routing in the 1960s, as long as you worked at IBM.

Image
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Re: Excelerator plus pcb repair warning

Post by eslapion »

Gyro Gearloose wrote: Sat Jan 04, 2020 7:15 pm I'm pretty glad I found a 74LS133 DIP here in Montreal. It was the only 74 family chip I didn't have in my crap.
You should've asked me. I have a couple left in stock from our 'cloning' experiment from 20 years ago.

I also have a bunch of 74HC133 but these will obviously require pull-up resistors on all inputs when used with TTL-LS level technologies.
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Re: Excelerator plus pcb repair warning

Post by Gyro Gearloose »

Well I think the problem now is I don't have the correct ROM images for this drive. Whoever had it before was probably experimenting on it and the EPROMs contain firmware for another variation.
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