Vic 20 restoration

[InMiseryWeSeekPancakes]

Hi I found a cheap vic 20 online for 34.99 bucks used and I consider that a bargain,

  I was already aware that it would not turn on but I tried to fix it so basically this is the cpu

 

and this is the ram module

 

 

and I have already checked out all the other componuts besides these

so what I want to do is check the address and data lines between the cpu and ram to see if theres any break. So assuming I would start with data line zero

nd 

 

and I look for current correct? Well i found out its all working in proper order so then

I decided to move on to the logic probe, I was able to narrow it down to the three bus transceivers, the hex inverter and the 555 timer.

I tested the 555 timer worked fine,  next I moved on too the hex inverter basically how it works is that there is 6 little inverters on this chip so just to make this easier to understand I am just going to look at one of the inverters which is pin 1 and 2, and basically whatever signal goes into pin 1 will be the opposite on pin 2, so if its high it gets turned too low or vice versa, I removed the cpu and video chip too make sure there is no activity on the board so when I check the pin 1 and 2 and there counterparts its not correct because pin 1 is low then pin 2 is low and that is not correct, that specific chip is the only chip on the board that is soldered on the board, do I just replace the board or can it be fixed?

@Energycore

[MrJoosh]

On 28/08/2018 at 4:32 AM, InMiseryWeSeekPancakes said:

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I'm no expert, but i think as long as you can find that exact IC or a completely pin-compatible, function-compatible replacement, you should be able to swap it out without issue (as long as you're careful and know what you're doing :))

 

I'm sure that there are more experts on here that will be able to give a more accurate insight though...

 

Just to check as well, you were feeding the required operational power into the chip when you tested weren't you? If the chip wasn't getting power for it's own internal control circuitry, then I don't think that the inversion would work.