Author Topic: 464 - no keys work and tape deck unresponsive  (Read 222 times)

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Offline backtogeek

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464 - no keys work and tape deck unresponsive
« on: 15:38, 06 November 20 »
Hi Folks,


I wonder if anyone can give me any pointers.


I got a 464 short board. initially it would not even power up, when I opened it none of the ribbons were connected or the connector from the tape deck.


Once I resoldered the power switch it switched on fine however no keys work at all, play ff/rw do nothing.


I opened it back up, reflowed the pins for the ribbons and the cassette deck connector, no dice.


I noticed that the 8? pin plug that comes from the cassette deck had a bent pin making the center 2 touch, I fixed that (it took ages and a magnifying glass) hoping that was the issue, some sort of short but nope, same issue.


I traced the power connections from the cassette deck to the keyboard and they have continuity, I also checked the 2 relays? (the things that touch the 2 little plates when you press play or in stop position) all good and have power when they should have.


I reflowed almost every solder joint on the cassette deck, cleaned and retensioned the pins for the ribbon cables and I checked the 8 pin connector from the cable end to the corresponding pin on the cassette deck board, all fine.


So I am a bit confused as to what to try next, I am wondering if it is crashing immediately when it is powered on, is that a thing with these? I have never paid attention in the past but does the cursor blink usually (it is static right now)?


I have also checked the grounds.


I did a bit of a search here first but cant find anything specifically like that, maybe I did not look hard enough but any tips or suggestions are welcome.

I do have another working one I could get out but its a long board so I don't know how viable swapping bits over to test is.




Thanks.


Ant.

Online Bryce

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Re: 464 - no keys work and tape deck unresponsive
« Reply #1 on: 16:00, 06 November 20 »
Hi and welcome,

The keyboard is scanned by IC101 (74LS145) and being read by the AY sound chip. One of these could be damaged.

Bryce.

Offline backtogeek

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Re: 464 - no keys work and tape deck unresponsive
« Reply #2 on: 15:36, 07 November 20 »
Thanks Bryce,


I will check that out later today.


Ant.

Offline backtogeek

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Re: 464 - no keys work and tape deck unresponsive
« Reply #3 on: 13:31, 20 November 20 »
I still have not checked this out, just updating so people reading it don't think I fixed it and never came back to report, time is a premium right now.

Online Bryce

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Re: 464 - no keys work and tape deck unresponsive
« Reply #4 on: 14:07, 20 November 20 »
I still have not checked this out, just updating so people reading it don't think I fixed it and never came back to report, time is a premium right now.

But, but... You promised you'd do it TODAY! :D

Bryce.

Offline backtogeek

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Re: 464 - no keys work and tape deck unresponsive
« Reply #5 on: 17:45, 20 November 20 »
But, but... You promised you'd do it TODAY! :D

Bryce.


Ok, so I reflowed the sound chip, I don't have an oscilloscope (I should get one), I checked the voltages on each pin and observed the following on the pins:


1. 0
2. 0.35 - 0.77
3. 0.32 - 0.70
4. 0
5. 0
6. 0
7. 0.36 - 0.64
8. 0.35 - 0.63
9. 0.32 - 0.72
10. 0.32 - 0.62
11. 0.38 - 0.59
12. 0.35 - 0.64
13. 0.35 - 0.64
14. 0.36 - 0.67
15. 0.14 - 0.47
16. 0.33 - 0.55
17. 0.35 - 0.72
18. 0.13 - 0.14
19. 0.36 - 0.57
20. 0.11 - 0.13
21. 0.34 - 0.61
22. 0.34 - 0.61
23. 0.35 - 0.57
24. 0.36 - 0.55
25. 0.35 - 0.59
26. 0.36 - 0.68
27. 0.35 - 0.61
28. 0.35 - 0.61


Not sure if that is helpful.


Keyboard still 100% unresponsive Right spindle does not turn at all either.

I have another coming in about 3 days, so if that one is working I can try swapping the chips over.

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Re: 464 - no keys work and tape deck unresponsive
« Reply #6 on: 19:59, 20 November 20 »
That doesn't really tell anything. What you could try with a multimeter is: Measure the voltage on pins 7 to 14 while a corresponding key is being pressed (a key associated with that input pin). This could possibly tell you whether the AY or the 74LS145 is the issue. However, these are fast changing signals, so a multimeter really isn't the correct device to use.


Bryce.