Help, please? Many carts work, Many do not

[Obiw4n]

1 minute ago, -^CrossBow^- said:

Replace the sockets and see if things don't work better then.

I have new sockets already on the way... hopefully they'll arrive tomorrow and If so I'll give it a try and report back.

[sn8k]

How different is the Jr to the big wooden ones?

[tubes_rock]

I FIXED IT!

 

Many thanks for the schematic. After a half hour of signal tracing and whatnot, I started to do some analog signal comparison using my scope. While the crude NMOS chips don't give nice clean signals like I'm used to seeing on newer CMOS stuff, it wasn't too bad. However, one thing was very clear: on the carts that worked, the data, address and RDY signals did what you would expect. They were busy and full of binary signaling. On the carts that did not work, they were dead. No activity. The oscillator was running, 3.5MHz into the TIA, and 1.1MHz on the Phase 1 line going into the CPU. The CPU was delivering 1.1MHz back out on Phase 2, so the CPU was doing the quadrature timing typical of the 6502-class CPUs. All good. However, nothing else was doing anything at all. That was pretty clear that the reset circuit was not allowing the CPU to go into a ready mode to start doing things. +5V on the RESET pin, which is active low, so that looked good. Then I saw that the 6532 chip had a reset pin as well, and it was +5 also, so that looked good. But, looking at the schematic, the +5 on both the CPU and the 6532 are fed (at least on the version 13 board that my 2600A has) through a 24k resistor to a capacitor. However, the cap value on both chips is different. On the 6532, it's a 1uF, and on the 6507, it's 4.7uF. That means that the 6532 should come out of reset first, since that cap charges to +5 quicker, and then the CPU should come out of reset and start working. However, on the scope, set to 20us sweep, I could see that the CPU came up to +5 instantly and the 6532 took a few milliseconds to come up, like it should. That meant that C201 was bad, having effectively 0.0uF of capacitance. I replaced that cap, and all carts work perfectly. Done.

 

Hope this helps!

 

--Justin

[tubes_rock]

And looking at ObiW4n's photos, that's the "mangled" cap I mentioned. Replace that with a good part, and I'll bet your machine works good too!

 

--Justin

[Obiw4n]

Thanks Justin, I just installed a new 4.7uF 35V capacitor at C201 and its working like a charm... lovely jubbly.

[tubes_rock]

23 minutes ago, Obiw4n said:

Thanks Justin, I just installed a new 4.7uF 35V capacitor at C201 and its working like a charm... lovely jubbly.

I love it when a plan comes together!

 

--Justin

[+DrVenkman]

This is honestly my first time hearing of a 2600 system with a bad reset cap anywhere, let alone two of them in the same thread. But I’m glad both of you got your systems working. And this is a good tidbit to keep in mind going forward when others report squirrelly issues like this in the future.

[+-^CrossBow^-]

3 hours ago, DrVenkman said:

This is honestly my first time hearing of a 2600 system with a bad reset cap anywhere, let alone two of them in the same thread. But I’m glad both of you got your systems working. And this is a good tidbit to keep in mind going forward when others report squirrelly issues like this in the future.

The refurb kits come with replacements for C201 on the H6 units so I replace them out as part of any standard refurb.

 

[tubes_rock]

I was thinking a similar thought: If I had not traced the actual problem through and just "shotgun" replaced all the electrolytic caps, the problem would have been solved just the same.

 

As an interesting side-note, on the 2600A, C201 is under the metal cover, where all the heat is. It's effectively in an oven. I suspect that's why it failed, while C214, which is exactly the same part, but near the RF Modulator where it can stay nice and cool, checked out at being 4.9uF (removed from circuit for testing), still in spec.

 

--Justin

 

[+DrVenkman]

7 minutes ago, -^CrossBow^- said:

The refurb kits come with replacements for C201 on the H6 units so I replace them out as part of any standard refurb.

 

What refurb kits? The ones Console5 sells? 

 

I mean, it’s fine that all the Nintendo Generation kids who grow up on systems from the late 80’s/early 90s that all have lousy capacitors just assume that every electrolytic cap on a vintage system needs to be replaced, but in my experience, it’s very rare for any Atari system to have bad caps. I’ve had one Vader that I did a recap on to get rid of noisy video but that’s it, over the course of 14 x A8 computers, 5 x VCS/2600 systems, 2 x 7800s and 2 x 5200’s. None of them have needed any kind of routine recapping, and Just Work (tm).  

 

But anyway, I’m glad these folks figured out their issues and it’s something I’ll keep in the back of my mind for future intermittent issues. 

[+-^CrossBow^-]

7 minutes ago, DrVenkman said:

What refurb kits? The ones Console5 sells? 

Yes, they have two versions of the kit. One for 6 switch units and another for 4 switch and Jr. models.

 

[Keatah]

Electronics' school will teach you to first check for proper voltage and oscillator and reset, when troubleshooting a microprocessor system.

 

Most vintage electronics of the Atari era are approaching 45-50 years of age. All electrolytics need to be replaced. Even though they may read their indicated uF rating, that's not good enough.

 

[tubes_rock]

Well, sure ESR changes and things, but my point was that the "bad" one measured 0.0uF and the "still okay" one reads close to its rated value. Since the "good" one is just a decoupling cap for the RF modulator, which is still providing good output, I'll call that "good enough." 1MHz systems are pretty forgiving when it comes to many things. And yes, my 4 year EE degree and 25 years of field work suggests that all the caps should be replaced, but if I replaced all components that "could" be bad, even though they spec okay, on every piece of gear that I work on, I'd owe Digi-Key more than I owe on my mortgage!

 

--Justin

 

 

[Keatah]

As of now it's only the electrolytic caps that need replacing. Not all, but the scope is expanding compared to 10 years ago.

 

IC's and carbon/film resistors, ceramic disc caps, diodes, and other parts are showing 50+ years life easily. EPROMS have data retention near 100 years, give or take depending who's data sheet you read and how the chip was programmed. And mask ROMS are supposedly good for 200 years or more.

 

I'm willing to bet we'll see failures related to wire insulation breakdown and electrolytic/galvanic corrosion sooner.

 

Not sure about poly caps, I would guess those are vulnerable. And tantalum caps - I hate those things! Except when they result in something failing and going up on ebay "for parts - does not work".

Edited July 28, 2021 by Keatah

[+DrVenkman]

18 hours ago, Keatah said:

All electrolytics need to be replaced

No.