svenpetersen1965/c64-diagnostic-rev.-586220-harness

A harness for the Diagnostic Rev. 586220 Test for the Commodore C64

c64-diagnostic-rev.-586220-harness's Issues

Control port shows bad on Rev2 harness

Sven, got several of your test Harness builds (in all versions) - but this latest non-SMD version keeps on giving me bad control port on all C64 boards (I have many) - I have replaced the 316Ohm resistor with a pot so I could dial in exactly 316, but to no avail - I have no clue as to why I can't seem to get this version of the harness to not show this (consistent) issue on all boards.....any ideas of what i could try out?

Modified case files

Diagnostic_Harness_Case_Mods.zip

Attached are modified case designs for the cassette and user port. The two screw posts are moved back and holes added for screws from card edge connector. This should work for both 3mm and #4-40 screws with nuts on the inside.

Also a 'sleeve' to protect the pass through edge connector for cassette port was added. It has keying bumps inside which just add enough friction to keep it in place.

DigiKey BOM for North American Part Numbers

Sourcing assistance part numbers from N. American vendor(s).

Diag Harness BOM (N.American DIGIKEY PNs).xlsx

LED is always on on Extended Keyboard Dongle

First off. This is a wonderful project. Thank you so much! I had so much fun building it and testing my growing fleet of C64s and 128s.
I also tried the extended Keyboard version with the single wire connection to the cassette board.

Here I noticed that the LED is always on, even when J2 is disconnected. I have placed R5 and removed R3. So it should be off if the jumper is disconnected.

It seems that R1 is too low. Even with the control line (IC1B Pin 4) pulled to low, there is enough current to turn on Q1. I have tried different values for R2 and R4. And I found that it works well if the resistances are raised by a magnitude. R2 = 10k and R4 = 47k. This gives the same well defined ctrl voltage for the high state (about 4,1V) but not enough current to turn on Q1 on the low state.

Here is a list of values that I've tried for R2 / R4 (also attached):

U_J2 is the voltage on Pin 5 of IC1B (the signal from J2)
U_A is the voltage in Pin 4 of IC1B
U_Q is the voltage on the base if Q1

You mentioned in your docs that you started out with R2 = 10k and it didn’t work. I noticed the same thing when R4 = 0. But it works well, if R4 is high enough (at the same ration of R2 / R4 as the current version).

I hope this makes sense. Disclaimer: Electronics is just a hobby of mine. I could be completely on the wrong track.
Regards,
Norbert

Ext_Keyboard_LED_fault.ods

Resistor values for R1 / R2 / R5 / R6 and R3?

Firstly, thank you Sven for sharing this. I'm looking to build one of these myself but when verifying the resistor values I think I found something odd. The documentation says R3 is a 320 ohm resistor, however in the photo it looks like something different (the others check out).

Looking at Jerzy Sobola's schematic on Zimmers.net R3 is a 300 ohm resistor rather than 320 ohm, he also uses 100k resistors for R1, R2, R5 and R6 rather than 120k.

I'd be very grateful if you or anyone else could help me understand why these are different, thanks in advance.

Paddle test indicates false failure on some boards

I ran into a board that kept failing the paddle test and insisted that either the SID or U28 (4066) was bad. The SID was known good, and tested fine in another board. I replaced U28, but the problem persisted. Reading through the original diagnostic cartridge manual, I noticed that Commodore used 110k resistors to pull the 4 POT lines up to +5v. The diagnostic harness here uses 120k resistors (R1,R2,R5,R6) on the user port to achieve the same. On a hunch, I changed these resistors on the user port of the harness to 110k. The diagnostic test is now passing every time without fail for this board.

Thank you Sven for all of your contributions to the retro community!
Dan Goswick

Missing Label on User Port Board

C4 is not marked on the User Port board. I figured it out via process of elimination, but depending on assembly order, it might trip some folks up. My boards came from PCBWay, but I verified in KiCAD.