Tipps for building the PAL-2

[Neil Andretti]

Wohooo. I've made it. My little PAL-2 is up and running.

There are some hints I want to give:

Take care about the orientation of the chips. Some point left, some right. Some up and some down. Double check it when soldering the sockets as well as when inserting the ICs

No one wants magic smoke.

The BOM says U5 is a 32x8Kb, but the 2816  is a 2x8Kb EEPROM,  don't wonder.

Make sure, if you want to use the serial connection that your USB3 cable is a data, not like the 1st one I've tried, just a loading one (why are those even produced? what evil person does such things?).

Have fun!

Nils

[John Kennedy]

Congrats!

I had to leave on an emergency trip the day my kit arrived, but I took it with me. Sadly I underestimated how well my usual soldering iron works, and had to use a cheapie one. As a result - I'm guessing - my PAL-II is not functioning very well. Specifically, the LED displays are _trying_ to display the digits 0 to F, but the patterns they light up are corrupted. Which chips define what makes a "0" look like a "0" and so on? That would give me a starting point.

-John

[Jim McClanahan]

Are segments off that should be on? Or on that should be off? Is it consistent on all digits (they are all missing a segment or have a segment lit that shouldn't be)?

The RIOT drives what turns on and off but does it through driver transistors. The details of how it is behaving would help narrow it down a lot.

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Thanks,

Jim W4JBM

"With a soldering iron in one hand, a schematic in the other, and puzzled look on his face..."

https://github.com/w4jbm

[GN Liu]

The U2 is controlling the onboard LED display.

Like Jim write, more detailed description of the behavior can help identify the issue.

[GN Liu]

Thanks Nils, the BOM description will be update later~

[John Calhoun]

Curious what Terminal software people are using to talk to connect to the PAL-2?

[GN Liu]

I use Tera Term on Windows and minicom on Mac

[Voyageur]

HyperTerminal on Win11

Minicom or gtkterm on Linux

[Voyageur]

And Serial USB Terminal on Android   

:roll:

[John Kennedy]

Hopefully this video clip works.. Update: I was unable to attach the video clip to this posting, so it's on several social media sites:

https://bsky.app/profile/kim-6502.bsky.social/post/3lhbefr32lk2y

https://www.instagram.com/reel/DFm5bR3ojr2/?igsh=bDM4YzBscXAya3cy

It shows that the patterns on the LEDs are mostly incorrect - but consistently incorrect.

One of the display devices has two segments out, so that seems like it might be broken. However, the others displays work - but display incorrect patterns.

I will research the LED display pin outs to see if this hints at a specific line being shorted or disconnected. And check if the segments are really broken.

Anyway, the video starts with the address set to 0000. I then press + to increment the address, and you can see instead of 1, 2,3,4, etc there are incorrect digits displayed. I then enter FFFF and a few other addresses, and again, the pattern displayed for each number is incorrect.

I did try writing to memory and it seemed to store the value, so that is a good sign. 

I also swapped the RIOT chips around to see if that made any difference, it did not.

Any advice very welcome. I'm at a hospital during the day, and this is a welcome distraction when I get home.

[Hans Otten]

Watched the video. Very likely you have solder bridges somewhere around the driver ICs or transistors. Desolder and reflow

Wish you strength with the hospital!

[Hans Otten]

I have built my PAL-2. Spread over a couple of days, I live slow! 

Just followed the interactive BOM,  passive components first, ICs last. 
Nothing special to note, compare yours with the photo on the PAL-2 Tindie site.

Orientation of IC sockets and IC's, check twice!

Check your soldering joints, not too much sodler, but covered with the right color solder.

And the three slider switches,: the SST keyboard one has a higher slider that the other two!

Please be careful with the Dupont power cables, double check the polarity! If in error: magic smoke!

I do not like the Dupont wires for power, serial, TTY switch. Too easy to make a mistake in the power connection.  

I am now designing and building a simple I/O card for the  Application connector, experimenters print, point to point wires, male pin connector to PAL-2, on board female connector for USB to Serial, power switch, TTY/Keypad switch.

That may grow later to SD or 1541 or Corsham SD card interfaces. 

[John Kennedy]

Thanks Hans.

I've reflowed every single joint, swapped like chips, scrubbed the flux off the board and cleaned it.. with exactly the same results. It's a puzzler.

Segment "f" is always on, although dimmer when not required. Same with Segment 'b". Except that is on the third display of the address set, when they are always off, which does hint at a short. I'll keep looking!

[John Kennedy]

Ah, there seems to be a short between these pins on the LED display. Is it possible for the LED display to fail and short? Seems odd.

[Jimmy Ipock]

So i'd swap the third transistor from the left with a different one... 
No change from that, i'd swap the LED with a different one.
Process of elimination.

On Tue, Feb 4, 2025 at 1:10 PM John Calhoun <softd...@gmail.com> wrote:

Just looking at the schematic, the 74LS145 looks like a candidate problem area. Double check every aspect of that chip install, etc.

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[GN Liu]

The daughter board design will start tomorrow.

[GN Liu]

An internal short circuit in the LED is extremely rare. I think you should check the soldering of the components directly connected to these two pins.

[John Kennedy]

Well, what do you know? It _was_ the LED display that was broken. I removed it, the short was gone, and things seem like they are working.

I have a replacement display on the way. 

Thanks for all the ideas, folks!

[GN Liu]

OMG..... a new failure point discovered.... I can refund you the amount you paid for the replacement LED.

[Hans Otten]

I know John has quite some experience soldering, but damaging LED displays is possible by overheating.

Two connections next to each other, happened to me also in the seventies.

 Since then I do it very slowly and give LEDs and ICs time to cool,  not two adjacent pins quickly  after each other, moving on to the next LED display and then back again to the first.

[John Kennedy]

Oh rude! I've been soldering for 40+ years! ;-)

But yeah, of course, accidents can happen. There's always a first time and this wasn't the best soldering iron in the world.

[Hans Van Slooten]

With enough heat, any diode can have its breakdown voltage reduced to 0.

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[John Kennedy]

[John Kennedy]

And all is right with the world.

[Ronny Ribeiro]

🥳🎉🎊

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[GN Liu]

Congratulations!!!!! 

When it displays normally, it is indeed a very beautiful LED 😍

[Hans Otten]

Congratulations John! 

All is well that ends well.