Junior model (likely) had a bad vreg, now just outputs colourful static

Brik_1111 · December 14, 2019

Hi everyone. I've been working on this broken 2600 Junior for the last week and since my huge amounts of research usually lead to this forum, you guys seem like the perfect bunch to ask since I'm now stuck.

A bit of backstory: I believe this Jr. encountered some tough times as the RF shield is very rusty. It turned on, but only tuned to a black screen. So on opening it up, the board was a bit messy but it did clean up quite well using isopropyl and white vinegar. I also reflowed a bunch of solder joints that were looking a bit dull, but this didn't change anything.

Just to clarify, the equipment I'm using to test this Atari (RF cable, game, power adaptor etc) have been confirmed with another working 2600 Jr I own. So, this rules out anything external - the problem lays somewhere in the Atari itself.

Onwards with the research, I learnt that the power regulator is prone to failure. Reading the pins, 9.03v was measured on one although the other measured at 4.93v - pretty low. So, I replaced that and it now read 4.98v and 9.06v - much better! The 2600 still wasn't working, however, now showing a colourful garbled mess of static instead of a black screen.

I then checked a few voltages over the board. 4.98v was tested going to the cartridge slot, the TIA, the RIOT 6532 and the CPU 6507. I also confirmed continuity to those chips by measuring between their Vss's and the ground pin of the vreg. This tells me the chips are powering on (I'm assuming 4.98v is adequate) but I do not own an oscilloscope to test that they're behaving as they should. For what it's worth, neither get too warm while the console is operating.

Hoping that it's not any of the chips that are the problem, I scoured the board for anything that seemed out of place. Two components stood out to me; C38 and R43. The legs on both were corroded and the pads below were a bit of a mess.

I have no means of testing the cap, but the resistor (when removed) measured about 8.8K oms, while according to the schematic it's supposed to be 9.1K. That was replaced easily enough, while the cap was replaced with a 0.1uF ceramic disk type - a recommendation I found in this thread:

Here are some photos of the replacements soldered in. They soldered in fine from the bottom of the board, but do you think the pads on the top are too corroded? I couldn't get any solder to stick. I'm not sure if they connect to traces on the top or not and if a connection is being severed.