Fix your non-working Atari 820 printer

[electronizer]

In a previous post I wrote about troubleshooting my Atari 820 printer. It’s been working solidly for more than a week now so I figured I’d post the solution.

 

The failure mode is that the printer won’t do anything after you turn it on. The power LED comes on, but the paper advance button doesn’t work, and nothing happens when you try to print from the computer. Every once in a while, the printer may work when you turn it on, or it may work for a short time and then stop responding (no paper advance or lprint).

 

Assuming you’ve already tried the standard “reseat the ICs” solution with no success, the fix is to replace capacitor C109, a 1uF electrolytic capacitor that forms part of the reset circuit. My guess is that this capacitor hasn’t aged well in many of the 820s out there, either losing some capacitance or developing a leakage current. Because of its small capacitance value, even a slight worsening causes the reset circuit to function poorly, and therefore the ICs in the printer may come up in an unknown (and non-functional) state.

 

In my printer, I chose to replace the capacitor with a 2.2uF part to increase the reliability of the circuit. I tried values up to 4.7uF and the printer still powered up and came out of reset fast enough that it wasn’t noticeable. A capacitor with axial leads would be best, but I made do with the radial lead part I had. Here’s a picture of the fix:

 

 

I attached the capacitor between R106 and R110. The R106 connection is a little tricky because there’s a via right next to the resistor lead and you need to be careful not to bridge the pads. I also clipped out the old capacitor in case it was passing a leakage current. You can see the empty pads at the left of the picture. The nice thing about this fix is that you don’t have to disassemble the printer, though you’ll need a small pair of precision diagonal cutters to get the old capacitor out. I laid the new capacitor on its side so that the RF shield would still fit.

 

If anyone has an 820 that still works reliably, I’d be interested to know if it uses the exact same part for capacitor C109. Mine had a blue Nichicon rated at 50V. Let me know if your printer has a different one!

 

 

[candle]

you might use 16V 1uF MLCC capacitor, size 805 will be a better fit for this and you still don't need to disassemble board to replace it

plus side is that you won't be doing this again - ever

 

[BillC]

On 9/2/2019 at 3:07 PM, electronizer said:

the fix is to replace capacitor C109, a 1uF electrolytic capacitor that forms part of the reset circuit

It's nice to hear you got it working, thought you should know that according to the 850 FSM that C109 is listed as a .001uF 25V capacitor. The only 1uF capacitor in the parts list is C35(16V/50V depending on version of FSM).

[joeatari]

I'm trying to revive an old 820 I found that had a broken fuse holder.  I have replaced the fuse holder.

I'm wondering what is the proper polarity of the capacitor in this fix?

I am experiencing the symptoms you describe, and also sometimes when I turn the printer on it will keep feeding the paper over and over until I shut off the switch.

Sometimes the paper feed button won't work and the printer won't print.

Other times the printer will function, at least for awhile.

 

Edited April 19, 2021 by joeatari

[joeatari]

When I removed C109 and added the 2.2 uf capacitor, my printer still behaved the same (not starting or continually advancing the paper).  When I removed the 2.2 uf capacitor described in the fix (C109 is also still removed), the printer starts up normally and the paper advance button works properly.  I need to test the printing function now.

[KLund1]

On 4/18/2021 at 6:50 PM, joeatari said:

I'm trying to revive an old 820 I found that had a broken fuse holder.  I have replaced the fuse holder.

 

I am missing the fuse cap on my 820 printer. What did you use to replace yours?

Perhaps a link so I get get one?

Thanks