board testing

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gillandro
Posts: 23
Joined: 17 Apr 2019, 15:57

Re: board testing

Post by gillandro » 13 May 2019, 00:06

i tested all the pins and based on the sheet it said might be some shift....for example a pin reading 0.595 is just about the 0.600v that the sheet says is good for pin being connected to load....but here are the pins i found anomalies on based on the spread sheet

u13 pin 5—.652
u19 pin 14–.430
u20 pin 14–.430
u21 pin 2—.434
u22 pin 2–.434 pin 10 —.900
u23 pin 2– .434 pin 10 .917
u24 pin 2—.434

i hope this sheds light on something im missing but a more educated man would see thanks

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marcelk
Posts: 331
Joined: 13 May 2018, 08:26

Re: board testing

Post by marcelk » 14 May 2019, 09:47

gillandro wrote:
13 May 2019, 00:06
u13 pin 5—.652
u19 pin 14–.430
u20 pin 14–.430
u21 pin 2—.434
u22 pin 2–.434 pin 10 —.900
u23 pin 2– .434 pin 10 .917
u24 pin 2—.434
That's good news. U13 pin 5 must be firmly connected to ground. Same for U22/U23 pin 10. High values are typical for an unconnected input pin.

U13.png
Mode decoder
U13.png (63.52 KiB) Viewed 458 times
U21-U24.png
Logic unit
U21-U24.png (214.11 KiB) Viewed 458 times


I wouldn't worry about the others. Those pins are also connected to the data bus.

gillandro
Posts: 23
Joined: 17 Apr 2019, 15:57

Re: board testing

Post by gillandro » 14 May 2019, 14:33

so a back cleaning might be all i need?

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marcelk
Posts: 331
Joined: 13 May 2018, 08:26

Re: board testing

Post by marcelk » 14 May 2019, 15:24

The purpose of the procedure is to find disconnected pins. I would re-solder those.

gillandro
Posts: 23
Joined: 17 Apr 2019, 15:57

Re: board testing

Post by gillandro » 14 May 2019, 16:56

can i flow solder in from the top? or do i need to rensolder from the bottom?

and based on what i sent....i know its probably me being confused but can you list the ones that need to be addresssed i see the pin 5 of u13

and the pins of u22 and 23 but which others as well. thanks

basically if i read you right i should just have

u13 pin 5
u22 pin 10
u23 pin 10 to resolder? im sorry for all the annoyance i prob generate...i guess im a solder noob lol

gillandro
Posts: 23
Joined: 17 Apr 2019, 15:57

Re: board testing

Post by gillandro » 14 May 2019, 19:24

getting there....u13 pin 5, u22/23 pin 10 now read 0.....i plug the board in leds 5-8 come on for a second then go out.....now what or am i missing a resolder joint thanks

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marcelk
Posts: 331
Joined: 13 May 2018, 08:26

Re: board testing

Post by marcelk » 14 May 2019, 21:49

The LEDs go off, therefore some code is running and part of the CPU is working as intended. This is what normally happens:
  1. At power on, the LEDs are in an arbitrary state. This might be 4 lights on, or 4 lights off, or some on and some off.
  2. The MCP will reset the program counter and freeze it for about a third of a second.
  3. The "Power OK" LED is off during this time, and the other LEDs can't change.
  4. After that duration, "Power OK" lights up and the software is allowed to run. It will go through the following sequence:
  5. Switch all 4 LEDs off
  6. Do quick RAM check
  7. Perform 10 ms delay loop
  8. Switch left-most LED on
  9. Full memory scan
  10. Switch second LED on
  11. Test for cold or hot boot condition
  12. Setup vReset routine
  13. Setup serial input
  14. Switch third LED on
  15. Setup the sound tables
  16. Switch last and right-most LED on
  17. Start video signal and continuous back-and-forth scanning LED pattern
  18. Load and execute Reset.gcl (this clears the screen and writes the top two lines of text)
  19. Load and execute Main.gcl (this makes the startup sound and shows the menu)
  20. Wait for user input while flashing the arrow
You now get past step 5 but don't reach step 8. That simply means that you have to continue with what you were doing: to look for bad contacts, and don't forget to check for short circuits between pins. Ask your soldering materials supplier how to treat residual flux, and follow their instructions (there is no way we can advice on that). Use the circuit diagram and multimeter to verify that pins of one component are indeed connected to the right pins on the other components.

All our tips and tricks are on the troubleshooting webpage. I don't feel it's necessary to keep repeating what is written there. However the most important piece of advice from there is this:
If you can’t find the bad soldering joint or short, assume you’ve missed it and look for it again!

gillandro
Posts: 23
Joined: 17 Apr 2019, 15:57

Re: board testing

Post by gillandro » 14 May 2019, 22:06

thank you...ill keep checking with my loup and meter if it doesnt work at this point its something i did wrong and i wont find it....i appreciate all your help....i will have to check the second board as well....if the same issues are there then im not sure what it could be as making the same mistakes 2x is usually rare.

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marcelk
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Joined: 13 May 2018, 08:26

Re: board testing

Post by marcelk » 14 May 2019, 22:23

Early on you have removed and replaced some the resistor arrays. Personally, I would carefully check (with a multimeter in continuity mode) that each of their pins are really connected. When removing a component, it's easy to accidentally damage the copper connection in the PCB. I would focus on the pins of R4 and R5, because those are critical for operation of the system. Use the schematic to find test points elsewhere on the board for each of their pins.

I once had a board where pin 1 of R4 wasn't connecting properly, and it didn't work... this was indeed after R4 replacement and the cause was a damaged trace: it didn't connect to nearby C16 anymore. You can sometimes fix such issue with some extra solder and bridge the gap that way. Otherwise you have to run a patch wire to restore the connection.

gillandro
Posts: 23
Joined: 17 Apr 2019, 15:57

Re: board testing

Post by gillandro » 14 May 2019, 23:10

thank you i will check those points...still need to test board two as i know those resistor packs are in properly

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