After composite mod some games don't work / power LED pulses 2600jr

[jason novak]

I have a 2600jr that has been disassembled a few years waiting for a composite mod which I've finally done now with a cheap kit off eBay > a few resistors and a  transistor. From what I recall everything worked fine before I took it appear

 

Some games work fine, like Jungle Hunt and Pole Position, but many others  - like Pitfall & Pitfall 2 - have no picture and it seems like it's power cycling, with the power LED coming on bright, then fading, and bright, every second or so. I've cleaned the slot, tried several power adapters including soldering directly to the board. Double-checked the mod and all seems correct. No obvious capacitor bulges. I tested it on a Commodore 1082 monitor and LCD TV, same issue and picture quality. I didn't use the 75 ohm resistor that came with the kit.

 

Seems strange some games work and  some put the system into a loop. I assume it's related to the mod, but something could have died while it was in storage

Edited August 4, 2020 by jason novak

[CommodoreDecker]

What would the Pitfall games be utilizing in the 2600's circuitry that the other still-working games don't use? (e.g. scrolling? )  That could yield a clue. It's not all games, so whatever's going on is definitely a more concise issue than a generalized one.

 

Is it possible to remove the mod and try the ailing games again and see if the problem persists? The composite mod could be defective in some way...?

 

Or there's still a chance of a small short circuit at or adjacent to a solder joint.

 

Are the 2600's chips socketed? One could have become just loose enough to wreak havoc on some games yet not others...

 

 

[jason novak]

Thanks, I double-checked the all of the modifications and everything looked good. It's a fairly basic one similar to the attached image. Unfortunately it's hard to reverse now as I just snipped off the parts per the instructions figuring I'd never need to go back... all the chips are soldered

 

I do wonder if it's something besides the mod since some work and some don't, I'd think all or nothing

 

I tried a testing a few games:

 

works: jungle hunt, enduro, spiderman, venture, popeye, ms pacman

doesn't work: pitfall, pitfall 2, chopper command, dragster, tomcat, dark chambers

 

pitfall justs shows garbage, the other games pulse the power button like the machine keeps reseting

[ChildOfCv]

It would be useful to see a high res picture of the board where the work was done too.

 

Assuming that soldering isn't the issue, there doesn't seem to be a correlation between ROM size and whether or not it works, so the next best issue may be the RAM (which is contained in the 6532).

[jason novak]

Sure, here  are two images
 

https://jason-novak.com/pictures/atari2600-1.jpg

https://jason-novak.com/pictures/atari2600-2.jpg

I followed this guide:
https://vintagegamingandmore.com/installation-guide-jr/
 

 

Edited August 5, 2020 by jason novak

[jason novak]

I touched all of the CPU pins with a little solder and cleaned up the  old flux and didn't help

 

Here's a video of what's happening, it's not super clear but the power LED dims every time the screen flashes / ticks

 

[ChildOfCv]

Well according to Kevtris's 2600 Jr schematics, the LED comes straight off the power input.  So if it's dimming, you have power problems.

 

As far as the capacitors go, bulges are one sign of failure but another is fluid stains underneath.  Do you see anything like that?

 

It may sound strange, but if you have a mechanical volt meter, it may shed some light on the power issue since the meter's movement is instantaneous.  Of course, if you have a virtual analog or fast response meter like what comes on a Meterman, that's potentially good too.  But I would expect to see some wild voltage swings while the system is doing its LED dimming.

[R.Cade]

Some games and not others? That is quite bizarre, but some cartridges use different pins for ground, etc. than others. 

 

You didn't happen to test it fully with the same games before the composite mod?

[jason novak]

Yeah that's the strange thing, it would make more sense if the mod was messed up and nothing worked, but to have some work and others not makes me unsure. I'm pretty sure it worked when I put it away, but I put it away disassembled pending this mod and it sat for a few years.

 

I believe it's getting the 5v from one of the pins from the removed transistor at Q4

 

No obvious leakage on the bottom, I did replace the 4 small 4.7uf caps just now and no difference, the old ones did test ok. I tested the big power one and  looks within spec.

[ChildOfCv]

Q4 is the audio modulator transistor.  The LED power comes straight after the power switch.  R57 keeps it from blowing up from 9V+ input.

 

You should keep the meter on C26's hot side to see if the voltage fluctuates while the system keeps resetting.  If it's holding solid, try the higher voltage side of R57.  If the voltage is unstable at R57, it could be that the power switch is dirty.

Edited August 6, 2020 by ChildOfCv

[jason novak]

I checked a second guide and they used the same wiring / q4 to 5v on mod:

http://www.retrofixes.com/2015/06/atari-2600-composite-av-upgrade-mod-kit.html

 

So with a "good" game I see 9v on the  + side of C26 when powered on, on a bad game I show 3v but can tell it's pulsing

 

The power switch does feel a lot looser than the color switch, ie doesn't click into  place the same way, but I tried circuit cleaner / re-soldering without change, as well as swapping the color switch in it's place

 

[ChildOfCv]

Not good.  Even the main power supply is pulled down to 3V?  Just to make sure, C26 should be that huge capacitor.  The smaller, tall one nearby is C37.

 

How many amps can your meter measure?  Assuming it can measure a good amount, like, say, 10A:

Place the meter in amps mode and connect the input power + side through the meter.  + would connect to the power supply wire and - would connect to the power input for the Atari.  Turn it on with a good vs bad game and see what the input current peaks at.

[jason novak]

I rarely test amperage and I think the 10amp fuse in my meter is dead probably from having it on the wrong setting at some point

 

But... I did fine the issue and it's working now. I went and got a universal power adapter now everything works. I'd tested the voltage on the  old one, and the fact that it worked on a number of games I'd not even thought about it. Still not clear why, but all good now. Thanks everyone for the help

[ChildOfCv]

Cool.  I guess the power supplies you tried have a shutdown mode if they think they are being over-taxed, and your game selection was right on that border.