Questions about Jailbars

[chowder]

When comparing your two systems,

Were the motherboard revisions the same?  The Famicom AV has HVCN-CPU-01 and HVCN-CPU-02, and the 02 has an extra electrolytic capacitor at C14 and uses a BU3270 instead of a BU3266 at U3.  

Were you using the same cartridges?  I have noticed that Nintendo manufactured-cartridges appear to be noise free, but other companies' cartridges can induce more noise.

How did you test the caps?  Without removing them, the reliable way to test them is by using an In-Circuit ESR meter, and they are expensive.  Also, the brand manufacturer of the caps may be different between the two boards, and some brands have better noise characteristics than others, so I have read.  

Also, make sure you are using the same power supply brick.  A poor quality or failing power supply can add noise to a console's video and audio output.

Yes, both CPU-02. 

Same cartridges, mainly SMB because the background usually shows the bars pretty clearly.  All legit carts.

I couldn't find a way to test the caps with them still in-circuit, but visually they're OK, and I thought if they were bad it might throw off the voltage readings somewhere else on the board, but everything was the same between out 2 units.

Same PSU used, it's a high quality multi-voltage one that I used with pretty much all of my old consoles without any problems.

[Great Hierophant]

Yes, both CPU-02. 

Same cartridges, mainly SMB because the background usually shows the bars pretty clearly.  All legit carts.

I couldn't find a way to test the caps with them still in-circuit, but visually they're OK, and I thought if they were bad it might throw off the voltage readings somewhere else on the board, but everything was the same between out 2 units.

Same PSU used, it's a high quality multi-voltage one that I used with pretty much all of my old consoles without any problems.

I would guess three possible issues :

1.  Age of the components increases jailbars, nothing you can do about that

2.  Quality control issues in the chips, again nothing that can be done

3.  Caps are failing, just not visibly or were second-rate to begin with.  Either test with an In-Circuit ESR meter or replace the electrolytic caps (there are only five on the CPU-02 board.)

[hvc01]

You're spot on with bullet point 1. Option is to get amother console or be happy with the one you have got. Not much else can be done unfortunately

[Great Hierophant]

I would recap the console and maybe even replace the three discrete transistors before writing it off to jail.