Trying to revive an 800, no color, low volume, keyboard doesn't work

[StickJock]

Final update:

Got the new 3086 chips in from AliExpress (only 5 weeks!).  Plugged one in and booted it up.  Color & sound back to normal.  WooHoo!

 

To summarize the repairs done:

Bad 16Kx1 RAM chip replaced with the spare chip that I had purchased in the early 80s.

Color & sound issues were due a faulty A104 (3086 transistor array).  Replacing chip fixed both issues.

Keyboard issue was due to a stiff/sticky/stuck keyboard membrane.  Carefully peeling the membrane off of the PCB and then reassembling it all fixed the keyboard issues.

PCBs all cleaned with electronics cleaning spray.

Case cleaned & brightened in the sun.

NOS OEM rubber feet installed.

New plastic rivet installed holding the PS board bezel/trim in place.

 

Joysticks & paddles work in all ports.  SIO works.  A/V & internal speaker works.  Basic cart works.  All keys work.  Looks like a successful resurrection.

 

BTW:  I left the dodgy looking caps & resistors in place.  They don't seem to be causing any issues.  I also unplugged & wrapped up the RF cable and tucked it into the big void in the side of the 800 case.  I covered the ends with electrical tape, just in case, to prevent any potential of them migrating & shorting anything out.

 

Anyway, the 800 is back in business.  Time to party like it's 1983!

 

[Colleton]

Nice.  Do you have a link for the plastic rivet you used?

[Kyle22]

On 3/2/2020 at 7:18 PM, DrVenkman said:

That resistor is toasted! I'd guess a static discharge, maybe through the TV. A lightning strike nearby maybe when it was plugged in? That kind of thing could also explain the dead DRAM chip and your keyboard issues. As for the keyboard, if swapping POKEY doesn't resolve it, the keyboard mux chips (the 4051 chips) would be the next thing to check. 

Sorry, but a static discharge doesn't have the amperage. Voltage will not blow a resistor. It requires CURRENT.

 

[StickJock]

4 hours ago, Colleton said:

Nice.  Do you have a link for the plastic rivet you used?

Sorry, I do not.  I found it in a sample box of assorted plastic fasteners that I had gotten about 15-20 years ago.  Yes, I am a bit of a packrat.  ?  It had several different sizes of the type used, and I found one that fit perfectly.

 

IIRC, it was a free sample box that I had ordered from a post on FatWallet (RIP).

[Colleton]

Okay, thanks. No  prob.

[StickJock]

22 hours ago, Colleton said:

Do you have a link for the plastic rivet you used?

Here's a pic of the box, and a pic of the contents.  I think that the one I used came from the left-most compartment.

 

Hopefully this will give you some leads.

 

[+DrVenkman]

On my Incognito 800, those exact same rivets are used to hold the system mainboard PCB to the bottom of the RF plate. They're also used to secure the SIO ports on at least a few of my various XL machines.