Problems with build

[Hans Van Slooten]

Hi Everyone,

I just recently completed building my PAL-1 and while the instructions are clear and straightforward, I must've made a mistake somewhere because when I plug it in, I don't get any display.

I checked all my solder joints and the orientation of ICs/caps/diodes/etc and don't see any problems (that's not to say I didn't make a mistake, I just didn't see any).

I hooked up a logic analyzer to the 6502 and 6532 and there's a clock signal, there's activity on the bus (it's repetitive, like a loop), but it appears that there is nothing on the PA0-PA7 pins of the RIOT. I have a second RIOT from the expansion and I tried that with the same results, so I don't think it's that chip. 

I dumped the ROM and compared it to known ROM images and it matches, so the ROM is fine.

I'm no expert with debugging hardware, so if someone could point me in a general area to troubleshoot to track down my mistake, I would appreciate it.

Thanks!

Hans

[Neil Andretti]

Good morning Hans,

could you provide us with some photos of the board? Maybe it's something obvious.

Nils

[Magnus Olsson]

One thing that’s very easy to miss is the setting of the two jumpers for TTY vs keyboard and on-board vs external memory. If any of them is set wrong, you won’t get any display. 

[GN L]

Hi Hans,

I also think some clear photos of the board (front and back) will help.

And, I want to try my luck, is the I/O selector jumper OPEN?

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Best,
Liu

[Hans Van Slooten]

Sure thing. 

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[Hans Van Slooten]

Yeah, I tried every combination of jumpers. I even tried to connect via serial, with no luck.

Thanks!

Hans

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[Hans Van Slooten]

I can also send logic analyzer output if it helps. I haven’t dug into the boot process to see what values should be on the bus yet, so I’ve only confirmed so far that there’s actually stuff going on.

[GN Liu]

From my eyes, the front side seems normal.

The back side looks dirty ;)  I think you can check all the solder joints again to make sure there are no shorts. From your photo I can see some possible shorted pins.

[Hans Van Slooten]

Thanks for your input everyone. As an update it still isn’t working, but I tested the ICs in my TL866II+ (everything except the RIOT, 6502, and 556) and they all checked out. The RIOT should be OK since I’ve tested two of them. I also cleaned up the flux on the board with some better cleaner and leaned off the “fuzzies” that looked like solder flags. I also did a ton of continuity checking to look for solder bridges, with no luck. I still have to do some more logic testing to see what the heck is going on. Here’s the cleaner board (I used a flash so it would be clearer).

Thanks!

Hans

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[GN L]

All solder joints look beautiful after cleaning.

I see you added keycaps on the switches, did you install the original switches from the kit or use some other switches with keycaps? If the switch is replaced, you need to check that the upper two pins are connected and the lower two pins are also connected. Like this:

1 2
o-----------o

o-----------o
3 4

Thanks,
Liu

> On May 19, 2022, at 11:03 AM, Hans Van Slooten <vans...@gmail.com> wrote:
>
> Thanks for your input everyone. As an update it still isn’t working, but I tested the ICs in my TL866II+ (everything except the RIOT, 6502, and 556) and they all checked out. The RIOT should be OK since I’ve tested two of them. I also cleaned up the flux on the board with some better cleaner and leaned off the “fuzzies” that looked like solder flags. I also did a ton of continuity checking to look for solder bridges, with no luck. I still have to do some more logic testing to see what the heck is going on. Here’s the cleaner board (I used a flash so it would be clearer).
>
> Thanks!
> Hans

> <IMG_5778.jpg>
>

[Ronny Ribeiro]

Hi Hans,

Some usual things to test: voltages and currents (to see if any of the components is shorted; you can also remove socketed components to rationalize this); swapped transistors (NPN by PNP and vice versa; I remember that there were different types in the circuit); if you have an oscilloscope, check for clock signals (pin 38 of the 6502 must have a signal).
I see from your picture it seems you messed with the rom (did you?). Be sure that it is working and properly burnt. If you are not sure, get the original (http://pal.aibs.ws/assets/PAL1_ROM_v1.0.bin) and burn it on an erased, blank tested EPROM chip (this last step is important, otherwise you may end up with garbage on the chip).
Good luck!

Ronny

[Magnus Olsson]

This is a bit of a tangent, especially since it didn't help in this case, but is there any practical reason for cleaning off the flux residue, except making it easier to see bad solder joints? I hear conflicting opinions on this: some say that cleaning off the flux residue is absolutely essential to ensure that the board works, while others don't seem to care. Apparently, at least some sorts of flux are corrosive and can damage the connections over time, and it is also claimed that it can attract moisture.

It obviously depends on which type of flux you're using, but I'm talking about the resin included in ordinary lead-free solder (the one I'm using leaves a clear, glass-like residue, not the brownish one that I remember from the bad old days of lead-based solder).

[GN L]

Thanks Ronny’s constructive instructions. But I just want to say the download link is for the ROM expansion, the right download link for the 27C64 on PAL-1 is http://pal.aibs.ws/assets/kim.bin

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Best,
Liu

[Ronny Ribeiro]

Oh, I'm sorry for that mistake! I simply forgot about the other ROM image XD

[Hans Van Slooten]

Per the suggestions, I did the following:

1) Tested that my switches were correct as described by Liu. They were, but to be extra sure, I desoldered mine and soldered the stock buttons. No difference.

2) Check the resistance of all resistors. They were correct. 

3) Checked for even more solder bridges, nothing found.

4) Tried swapping in a 65C02 chip to see if my processor was bad. No difference (not even sure that model would work in this board, but I'm getting desperate).

5) Checked the clock signal, that is correct. 

6) I can even get one of the displays to show an "8" by shorting pin 7 on U1 to GND. So, I'm sure the LEDs are working.

7) I did take the sticker off the EPROM before, but that was so I could get the chip version for reading. I wanted to get an image of the chip to compare to other ROM image to make sure it wasn't corrupted. It was fine.

Looking at the different signals on the board, there is clearly activity, it just, for whatever reason, isn't the right activity. I have to trace how exactly a digit is sent to the display so that I can try to trace where in the process it is getting thrown off.

Thanks,

Hans

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[GN L]

The old R65C02P can work on the board except for the SST function and some activities need using interrupts, you can light up the display and do basic operation like key in a program, terminal operation even play the lunar lander with R65C02P. But the newly produced WDC W65C02S cannot work with this board.

Thanks,
Liu

> On May 20, 2022, at 2:12 PM, Hans Van Slooten <vans...@gmail.com> wrote:
>
> Per the suggestions, I did the following:
>
> 1) Tested that my switches were correct as described by Liu. They were, but to be extra sure, I desoldered mine and soldered the stock buttons. No difference.
> 2) Check the resistance of all resistors. They were correct.
> 3) Checked for even more solder bridges, nothing found.
> 4) Tried swapping in a 65C02 chip to see if my processor was bad. No difference (not even sure that model would work in this board, but I'm getting desperate).
> 5) Checked the clock signal, that is correct.

[GN L]

Are you checked the resistor network under the processor is in the right direction? The white dot needs on the right (the print on the resistor network needs face to the IC socket), it’s seems wrong direction from your photo (very hard to identify because of the photo angle)

> On May 20, 2022, at 2:12 PM, Hans Van Slooten <vans...@gmail.com> wrote:
>
> Per the suggestions, I did the following:
>
> 1) Tested that my switches were correct as described by Liu. They were, but to be extra sure, I desoldered mine and soldered the stock buttons. No difference.
> 2) Check the resistance of all resistors. They were correct.
> 3) Checked for even more solder bridges, nothing found.
> 4) Tried swapping in a 65C02 chip to see if my processor was bad. No difference (not even sure that model would work in this board, but I'm getting desperate).
> 5) Checked the clock signal, that is correct.

> To view this discussion on the web visit https://groups.google.com/d/msgid/pal6502/CANf3X5X-73gSNbf%2BMmfX%2BHCM3scm%2BL5ATAmMRzy4W2cTJiABrg%40mail.gmail.com.

[Hans Van Slooten]

Yep, that's fine. 

[Magnus Olsson]

The LED segments are connected in a matrix with segments being selected by the outputs of U13 (pins 2, 4, 6, 8, 10 and 12) except for segment D which is connected to pin 5 on U2, 

while the digits are selected by pins 5-11 of U1. Did you check that you get signals on those pins?

[Magnus Olsson]

Correction: pin 8 on U1 is GND so the digits are selected by pins 5-7 and 9-11.

[Hans Van Slooten]

So, minor update. I hooked up a logic analyzer to the 6502 address pins so that I could see what the processor was doing. It looks like it's getting stuck in a loop in this code:

I've attached the logic analyzer output in CSV format. Not sure why it would loop there yet.

Here's what it looks like visually after reset:

Thanks,

Hans

[Hendrik-Jan Megens]

Hi Hans, 

great work on finding where your PAL-1 gets stuck. Which logic analyzer did you use for this?

I'm not sure if I can be much help - what strikes me is that there is a reference to two memory addresses of the RIOT there. You mentioned you tested both of them, but did you swap them out?

I know this is very frustrating for you, but I'm sure you will solve it! If it means anything I'm following this thread closely and learning from every step. So thanks for posting!!!

Hendrik-Jan

[Magnus Olsson]

OK, that code is listening to the RS232 input. You should only end up there if the keyboard/TTY jumper is closed.

If you follow the program flow from a reset, you can see that the state of this jumper is checked by the BIT instruction at 1C31. If the jumper is open, you skip this code and go to START instead, which interacts with the keyboard and display. 

So if the jumper is open and you end up where you are, you have a hardware problem either with the jumper or the circuits connected to it. 

If the jumper is closed and you are connected to an RS-232 terminal, then there seems to be something wrong with your RS-232 interface.

This is my reading of the code, anyway. I may have missed something.

On Friday, May 20, 2022 at 5:39:10 PM UTC+2 vans...@gmail.com wrote:

[Jim McClanahan]

You're spot on. That code is for initialization of the RS-232 timing constant. So that would seem to indicate 1) the jumper to enable serial communication is shorted, 2) the RIOT is bad, or 3) U1 is bad. If U1 is bad, nothing "stand alone" is going to work--the serial detection jumper, the keyboard, and the multiplexed LED driver all go through that. Since you seem to be dumping to the serial routine, I'd hook a terminal up and see if you can get to the monitor prompt. If so, that would narrow it down to the LED & Keyboard / Serial Port selection and probably mean U1 is bad if there are not problems with solder bridges or cold solder joints.

Thanks,

Jim W4JBM

[Hans Van Slooten]

PA0 is held high even before reset, and the jumper isn't shorted. When
I short the jumper, PA0 is held low. I believe that is the port that
it looks at for determining IO source.

I wasn't able to open a serial connection with the jumper in either
position, although introducing the USB-to-Serial and null modem cable
into the mix also increases the chances I made a mistake.

Hendrik-Jan: For logic analyzer, I just use Salaea Logic 1.2 with a
cheap 16-channel logic analyzer from eBay. I think you can get them
for like $50 US (I got mine a few years ago, but they haven't really
changed.) I think Salaea is changing their software with version 2.0
to stop these kinds of knock offs. I would happily buy one from them,
but at $1400, it's a bit much for a hobby. I'll be using version 1.2
for a while, I think.

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[Jim McClanahan]

I'm going to have to think on that a bit. U1 should be HI on pin 4 until the ROM sets PB4, 3, 2, and 1 to 0011. That pulls it low and then the RIOT would check PA0.

That kind of makes U1 suspicious. But if the serial link really doesn't work, that would point to the RIOT.

I'd probably also do some continuity checks. A bad via might cause something like this.

The good news is the CPU, RAM and ROM all seem to be working.

Thanks,

Jim W4JBM

[Hans Van Slooten]

I’ve tested all the logic chips in my TL866 II+, but that doesn’t necessarily mean they are good. I also tested using my second RIOT from the daughterboard, with no luck, so I’m still leaning towards my dodgy soldering skills. I’m going to do a complete once over with continuity checks just to confirm I didn't miss anything.

Thanks!

Hans

[Hans Van Slooten]

Well, I continuity checked everything, scoured the board for any possible bridges and I’m pretty sure those aren’t the issue. 

Since I was able to test the logic/sram/rom ICs and they came back good, and the processor seems to be doing its thing properly, I have to assume the RIOT is the issue. I should say RIOTs, because I have two and it doesn’t work with either of them (which is the one thing keeping me from saying I’m sure that’s the issue). At the very least, I’m going to get some 74LS145s to see if replacing those helps, but I’m also going to order some 6532s as well.

Thanks,

Hans

[GN L]

Very hard check!

But that’s weird, I checked every recycled vintage chip (6502 and 6532) when I received them from the seller and only kept the good ones. I got one report before that a 6532 went wrong after a few days of use, because these chips are old, the reliability may be at risk. But it doesn’t work from the first time and two 6532s are all failed, the possibility is very low.

On the other hand, from your testing process and phenomena, it is most likely that there is a problem with the 6532. I checked your order information, the purchase is within 90 days, so I will send you two double checked 6532s for the replacement hopefully that will help you to figure out what’s wrong.

Sorry for the bad experience.

Best,
Liu

> On May 22, 2022, at 2:51 PM, Hans Van Slooten <vans...@gmail.com> wrote:
>
> Well, I continuity checked everything, scoured the board for any possible bridges and I’m pretty sure those aren’t the issue.

> <IMG_5802.jpg>

[GN L]

And the TL866 II+ can also check the 74LS145.

Btw, the 74LS145 with the kit are brand new chips.

Best,
Liu

[Hendrik-Jan Megens]

Hans, are you by any chance living in The Netherlands? (wild guess re your name). 

I have spare parts I might be able to send you quickly. I can send you one of my RIOTs to try it out, if you DM me your address. Catch: I'm away for work all week so that would have to be before 16:00 this Sunday (or it will be sent next wekend but might still be faster than Liu sending you spares, esp. with current logistics challenges in China).

I was wondering - can you be sure the RAM is not compromised? Looking at the startup sequence you seem to be hanging just after a return from subroutine which means use of stackpointer and therefore RAM. If the RAM is faulty all sorts of weird things can happen I guess? I don't know by heart I have to look it up but I think the RAM can be checked with the TL866II+ 

Btw, for the most awesome chiptester, this is very sweet: 

https://8bit-museum.de/sonstiges/hardware-projekte/hardware-projekte-chip-tester-english/

Not being too experienced that was a difficult build (as was, btw, my PAL-1, I was even less experienced then!). But it is insanely useful for testing chips. Unfortunately it doesn't test larger chips like the 6502 etc. 

Let me know if sending you a spare is useful. Whatever happens, I *almost* feel jealous because by the time you have the PAL-1 working you'll be an absolute expert on it's workings!!!

Cheers,

Hendrik-Jan

[Hans Van Slooten]

Hendrik-Jan,

I actually live in the U.S. My great-grandfather moved to the U.S. and
my parents gave me a relatively Dutch first name, but that's about the
extent of my "Dutchness". :)

I've ordered a pack of RIOTs from eBay but, yeah, it'll probably be a
month before they arrive. I have a few logic chips coming from Mouser
that I'll be able to test this week, though. I have plenty of
projects, so this one might just have to sit on the shelf for a bit. I
would like to get that chip tester eventually. It looks pretty useful
for retrocomputing.

I've actually built a 5150 clone board, C64 clone board, PiDP-8, and
PiDP-11 before with surprisingly few issues. I was overdue for a build
issue. I've probably learned more from this little board than I did
from any of those other soldering projects.

Thanks for the offer, though.

Hans

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[Hans Otten]

Hope the problem can be found!

Two bad 6532's is possible but unlikely., as they were tested before. If the first one had a short circuit on an output  due to a solder bridge/PCB error/other logic IC error it may have died The second one then shared the ill fate 
So make sure all pins are not short circuited! before you insert another one.  

So check all pins of the RRIOT for short circuits to ground/power/other outputs of other IC's or not connected.  

[Hans Van Slooten]

That’s a good sugges