Extra capacitor(?) on bottom of 400 motherboard?

[Smokeless Joe]

I recently got a 400. The last time I had a 400 was probably 30 years ago, so it's been a while. When I turned the motherboard over, I saw this:

 

 

Here's a closeup of the section in question:

 

 

I think it's a capacitor and it looks like it's going from POKEY pin 17 (5 V power) to C137 (dunno what that does). The system seems to run just fine, although I haven't tried any diagnostics other than playing Star Raiders and plugging in a BASIC cartridge, a 410 and loading Invitation to Programming 1.

 

There was an Atari Service sticker from Carmel, NY on the bottom of the case, so that suggests it's had some work done. Any ideas what this is for?

 

Thanks,

-Joe

 

 

 

 

[+save2600]

That's clearly a resistor and looks to be a factory job and not uncommon to see stuff like that. May be a revision of some kind.

 

-edit-

 

Well I'll be a son of a gun!

[Bryan]

Two main possibilities:

 

1. A modification was specified on the production line and so someone added the caps before they left the factory. Once production has started, there can be a lot of hand rework done before it's more economical to make a new board to fix an 'oopsie'. Sometimes the added parts simply make the board more stable and aren't to fix an error per se.

 

2. It also could have been done at a service center, which means there's probably a service bulletin out there somewhere about it. When I worked at ICD, I remember seeing a LOT of Atari service bulletins about various problems and their cures. I don't think we're anywhere close to having an archive of them all.

[Bryan]

That's clearly a resistor and looks to be a factory job and not uncommon to see stuff like that. May be a revision of some kind.

 

Not necessarily. Caps come in that package too. Look at this picture of the top of a 400 mobo. The pink epoxy is a hint that it might not be a resistor.

[Smokeless Joe]

Bryan beat me to it! I thought it was a resistor at first but then I saw the caps exactly where Bryan points them out. Who knew? Not me, that's for sure.

Edited May 22, 2016 by Smokeless Joe

[BillC]

One way to tell is resistors have 4 bands, capacitors have 5. The extra band is for the voltage rating.

 

This type of capacitor is used a lot in the 130XE.

[Bryan]

Precision resistors can have 5 as well.

 

A 40.2K 1% resistor will have a band for 4, 0, 2, Multiplier band, Tolerance.

[JoSch]

I have this fix on my 400 board, too.

[+orpheuswaking]

I have seen probably 15 400s and seen this mod in various positions of the motherboard on at least 75% of them

[Smokeless Joe]

It's reassuring that this seems to be a common mod. Thanks!

[slaanesh]

I recently replace all my caps on my Atari 400... Does this type of cap also need replace like the electrolytic ones? If so what specs is this thing?

 

And yes, I also have this cap on my motherboard

[xrbrevin]

its rare for any caps to need replacing

[slaanesh]

I'm just trying to troubleshoot my Atari 400 and adding a 48/42K board. I replaced all the caps on the power board and a single cap on the motherboard - but I found out there is this extra cap underneath.

For completeness, I want to update it with a modern equivalent... does anyone know what the rating of it is?

[+DrVenkman]

1 hour ago, slaanesh said:

I'm just trying to troubleshoot my Atari 400 and adding a 48/42K board. I replaced all the caps on the power board and a single cap on the motherboard - but I found out there is this extra cap underneath.

For completeness, I want to update it with a modern equivalent... does anyone know what the rating of it is?

Can’t read the color codes through the translucent tubing in the OP’s photo so I can’t tell you the value. Get a clear photo of it and you can consult a capacitor color-band guide to determine the value.

 

That said, caps in Atari’s very, very rarely need to be replaced unless they’re bulging, leaking or somehow obviously failed (shorted to ground or failed open). You’re doing a lot of work for probably nothing. 

[Colleton]

2 hours ago, slaanesh said:

I'm just trying to troubleshoot my Atari 400 and adding a 48/42K board. I replaced all the caps on the power board and a single cap on the motherboard - but I found out there is this extra cap underneath.

For completeness, I want to update it with a modern equivalent... does anyone know what the rating of it is?

People (rightly or wrongly) replace the electrolytic capacitors because they have an electrolytic liquid/paste inside that can dry out or chemically change over time.  Small capacitors like this one do not need changing.