Jump to content
IGNORED

2600 DIY AV mod quesiton


eizner23

Recommended Posts

Just put together my own AV composite mod using 2N3904, 2.2/3.3k 1% metal film resistors, 22g solid core wire. I removed the RF box,  one transistor and one resistor.  The transistor I used is Motorola with hfe of 350.  I havnt put the two shields back on, my initial test was good, the colors pop more and the sound is more prevalent. I am getting a slight band rolling vertically on the screen, from bottom to top. I couldnt capture an image of it on my camera it was so slight.  Will this interference go away once i reassemble the 2600 [4 switcher] and its shields, or is from the wires being twisted? Also, should I omit the red tuning capacitor? Any opinions and other recommendations are welcome, and thanks. Also curious on a source for cheap Nichicon 2200uf 35v axial for filter cap, best I could find was $3.50 a pop on mouser for Illinois Capacitor brand. Seems impossible to use a radial in this spot due to clearance from top case.

 

2600-1.thumb.jpg.3893d3ebf5d642f1a2a88f50ed84d8e8.jpg2600-2.thumb.jpg.13abdf48d35f56d38777b73e875c6c68.jpg

Link to comment
Share on other sites

Not a pro, just an average Joe.

 

It sounds like your following a mod similar to this:

https://www.thefuturewas8bit.com/2600_comp_mod

 

Or maybe this:

https://www.instructables.com/id/ATARI-2600-Video-Composite-mod/

 

Can I just ask that if you are following a specific mod to follow that mod, and you should be okay.  If you're doing your own thing then I would expect you to know what you're doing.

 

That being said you're indicating there is some spurious RF present in the video signal presented as a band moving vertically up.  That indicates a cyclic frequency a good indicator of the mains supply, if not local RF noise.

 

I'll assume your soldering is good/clean and there are no shorts.

 

I'll also assume you've replaced any faulty capacitors, as they would filter out spurious interference.

 

I'll also assume all the chips are correctly in there sockets if applicable.

 

I'll then assume there is no nearby circuitry causing such emissions to affect the video signal.

 

I'll assume your voltage regulator is not on its' way out and failing, although it's my first candidate for suspicion if the above is all in order.

 

Finally I'll ask you to confirm the power source is correctly rated and delivering the right output.  I'll say 9volts and somewhere between 600mA to under 2A should suffice (I like a little under 2A).  If it's an old linear brick, how is it buzzing.

 

Good luck!

Link to comment
Share on other sites

Hi, the 2600 needs a little work still. Sometimes it doesnt turn on after a cold start then it comes on. Power switch was rebuilt and seems fine. Perhaps the voltage reg is not up to task. Still has original nichicon vx 2200uf filter cap, rest are new.

 

I plan on replacing the reg today if I got one and the cap soon.

 

No other interference I can think of and I yes I used that indestructibles circuit. Power source is new, use it on other 2600s.

 

Thank you for the info!

Link to comment
Share on other sites

I have LM340T 7805 on hand, 5v 1.5a output, I'll give that a shot.

 

...And it didnt help, made the banding a little more prevelant.  It's like two wavy RGB patterns slowly moving up vertically.

Tried giggling and touching the new wires that were introduced. Reflowing the filter cap. Didnt notice a difference.

 

Edited by eizner23
Added result.
Link to comment
Share on other sites

23 hours ago, eizner23 said:

...And it didnt help, made the banding a little more prevelant.

I'm becoming more suspicious of the voltage circuit after reading this.  I'm not sure this replacement part is within spec, I'd replace it and restore the original component as you don't have another.

 

On 4/15/2020 at 8:54 PM, Voxel said:

I'll assume your voltage regulator is not on its' way out and failing, although it's my first candidate for suspicion if the above is all in order.

When I mentioned the above I should have mentioned there are capacitors down stream of a voltage regulator that smooth out the voltage ripple.  I should have pointed you there.

 

Did some searching to save myself some typing, you may want to take a peak here:

 

Link to comment
Share on other sites

23 hours ago, eizner23 said:

constant 5.09 under load.

Thank you for correcting me, it sounds like the 7805 is well within spec.

 

Changing the 2200uf is worth considering based on the general health of the VCS, if there was any benefit in replacing other capacitors, then I would agree in changing it, in the long term it would be of benefit either way.  The mylar capacitor should last for a very long time, unless subjected to silly voltage/ambient conditions, its' insulation should be fine.

 

The image is still an indication of some cyclic pattern, again the most common suspects are alternating current (voltage supply) and the some localised RF signal bleeding through into the video circuit.

 

Taking a step back we know the original RF signal via the modulator was well shielded.  What we've not discussed is the earthing/shielding of your replacement circuit.  There are some long wires - try moving them and see if the interference changes.  In an earlier post #3, I linked the future was 8 bit.  Please read/study that modification with regards to the gound plane used.  The VCS circuit is naturally emitting local RF noise and the video modification may not be protected enough.

 

On 4/15/2020 at 8:54 PM, Voxel said:

I'll also assume all the chips are correctly in there sockets if applicable.

Please confirm the above, the IC's contain lots of transistors and when not correctly seated they can do weird and wonderful things (output wise).  I understand that you only added an AV mod and would have not interferred with them, but sometimes the boards can flex under a little stress.

Link to comment
Share on other sites

Not sure if it helps or if it's the same thing but I work for a CCTV company we call the rolling lines humbars.

 

In CCTV systems these are usually caused when there are two earth's which create new circuit we call groundloops. The monitor thinks this is part of intended video signal and tries to display them resulting in humbars.

  • Thanks 1
Link to comment
Share on other sites

57 minutes ago, LiamIsaacs said:

In CCTV systems these are usually caused when there are two earth's which create new circuit we call groundloops. The monitor thinks this is part of intended video signal and tries to display them resulting in humbars.

That's the kind of thing I'm getting at, glad you mentioned it.  There is a good indication the earthing/shielding is lacking.

Link to comment
Share on other sites

Thank you gentleman the ground issues makes sense. I read the first link in post #3 and that seems to be a better solution, and his initial issues match my issues.

 

I'm going to redo my work and use the ground plane as advised. I'll let you know if the results are work out.

Link to comment
Share on other sites

I tried the av mod from the future was 8 bit site. It's circuit is little different, the circuit I was using had no resistors on emitter. I gave it a shot and couldn't get any video, I tried two different boards! Old one still worked.

 

More digging I found a circuit using two transistors, the author described the same issues I had with the one transistor circuit. 

post 13 here 

20200422_144352.thumb.jpg.f774dae52e6307d2115219e93f0fa477.jpg

 

Doubled checked work and tossed it in. Identical results to my first board, and the graphics became more blurry on the right edges of graphics. The wavy band wasnt as prevelant but still there.

 

I removed more parts from the old RF, I x'ed parts I took out below. Put in new 2200uf cap. Reseated 2 of 3 chips, not the one under cartridge port yet. Wrapped the output wires once in a ferrite core. Nothing changed. Ha! I'm going to probe around with my scope, check parts upstream, see if I'm getting 5v to the new board. My testing of new board was done without the shield over the chips.

20200422_144614.thumb.jpg.b41c94e39a91ae76cd5d731437df03f0.jpg

 

 

 

Link to comment
Share on other sites

The power supply I was using is the Retro2600, a super light, switching PS with 9V output at 500mA.

 

As alternative I used my bench PS set to 14VDC and the wavy vertical scroll issue went away. 

 

I read original atari PS puts out 14v. Is there a better replacement solution? Maybe I can make my own using old laptop supply for now. Curious what the out current was with original.

 

The only issue remaining is the gfx terribly blurring to the right. Confirmed 5.08v getting to the composite board.

Link to comment
Share on other sites

On 4/15/2020 at 8:54 PM, Voxel said:

Finally I'll ask you to confirm the power source is correctly rated and delivering the right output.  I'll say 9volts and somewhere between 600mA to under 2A should suffice (I like a little under 2A).  If it's an old linear brick, how is it buzzing.

 

21 hours ago, eizner23 said:

As alternative I used my bench PS set to 14VDC and the wavy vertical scroll issue went away. 

Thanks for finally checking the power supply thorough enough to confirm a supply issue for yourself.  For the 7805 to work it will want to see 9v (but not too much above), for the correct 5v output regardless if it's 14v from the bench PSU or 9v from the cheap modern switching PSU.  As I indicated above and something you've omitted from your findings was the amperage rating is the missing variable in your puzzle.  Please ensure your replacement PSU can do more than the prescribed 500mA.  On checking your bench PSU's output amperage you can see that 500mA was not sufficient.  As indicated above ensure your replacement PSU should be under 2A (somewhere between 1A-1.5A should be ample).

 

The simple way to get a good PSU is type "9v 1A PSU" in ebay.  Choose which ever takes your fancy.  Then change the connector to a mono 3.5mm jack as centre positive.  The choice is bigger this way and you don't get ripped off like a noob chasing "2600" branding on a product.

Link to comment
Share on other sites

33 minutes ago, Voxel said:

The simple way to get a good PSU is type "9v 1A PSU" in ebay.  Choose which ever takes your fancy.  Then change the connector to a mono 3.5mm jack as centre positive.  The choice is bigger this way and you don't get ripped off like a noob chasing "2600" branding on a product.

And thank you for posting useful info! Must appreciated. I will set my quest to find an optimal power adapter, and ordered 3.5mm male mono Jack's just in case.

 

I'll hold off until the power source is resolved.

Link to comment
Share on other sites

56 minutes ago, eizner23 said:

And thank you for posting useful info! Must appreciated. I will set my quest to find an optimal power adapter, and ordered 3.5mm male mono Jack's just in case.

 

I'll hold off until the power source is resolved.

Not sure where you are located...but Console5 has a good power supply replacement for 2600s in stock on their website for what I would consider a good price:

 

https://console5.com/store/power-supply-adapter-for-atari-2600-and-atari-dedicated-systems.html

 

It is only rated to provide 500mA but that is the exact match of the original power supply as well.

 

Link to comment
Share on other sites

17 hours ago, eizner23 said:

I will set my quest to find an optimal power adapter, and ordered 3.5mm male mono Jack's just in case.

Just so you understand the options you have.  I've got a generic image of the type of PSU I'm using.  Which I've modified, plus it's in the style of a brick, not some inferior wall plug.  The importance of this PSU type is that it takes a generic figure of 8 cable from the mains side.  So I have a figure of 8 cable which can be any length from 1m to 5m or longer to suit my set up.  Of course I've also made sure it's fused to below 3 amps.  You would fuse to what fuses are available to you.  My PSU is 9v, 1.66amps in output, a 5m length figure 8 cable fused to 2amps.

 

Sample PSU.jpg

Link to comment
Share on other sites

On 4/24/2020 at 8:48 PM, eizner23 said:

The power supply I was using is the Retro2600, a super light, switching PS with 9V output at 500mA.

 

As alternative I used my bench PS set to 14VDC and the wavy vertical scroll issue went away. 

 

I read original atari PS puts out 14v. Is there a better replacement solution? Maybe I can make my own using old laptop supply for now. Curious what the out current was with original.

 

The only issue remaining is the gfx terribly blurring to the right. Confirmed 5.08v getting to the composite board.

The original power units output around 14V off load, that drops to around 9 volts when on load (powering the 2600). This is because when you take more current from a transform that it is rated for you get voltage losses within it (and heat). Manufactures take advantage of this fact to both get a psuedo output voltage regulation and to be able to use smaller, cheaper underrated (i.e. 300mA) transformers in their power units.

 

The advantage of using a linear regulated (a.k.a. stabilised) or switching power unit is that the output voltage is always at the specified voltage whether it is on load or not, the disadvantage with switching supplies is that the high frequency switching can create a lot of noise on the output which is often not filtered out at the source as well as it should be.

Consequently, it could be that switching noise either radiated (shielding will help) and/or travelling along the power rails is what is causing the video interference, if your bench PSU is non switching (liner regulation) that would strongly suggest that it is the switching noise from the Retro2600 that was causing the interference.

I presume your bench PSU is voltage regulated in which case you should set it to 9V when using it to power the 2600 to avoid excessive power dissipation in the 7805.

 

If switching noise is indeed the cause of your problem then using an old laptop PSU may well cause the same problem, if it is the size of a house brick you may be OK but if it is a modern slim one it will be switching (as are those of game systems like the Wii and PS) and so if the switching noise is entering via the power cable using any switching power unit may well put you back to where you started unless you install sufficient additional noise filtering on the power input to the 2600. Filtering could be as simple as a placing 0.1uF (100nF) ceramic disc capacitor across the power socket, but you may have to get a little more advanced and try a low pass filter, a cut off frequency anywhere from 500 to 1000 Hertz should suffice.

Link to comment
Share on other sites

I found an old heavy 9v 1A linksys wall adapter that is working fine, the power issue is sorted out thanks everyone for the help.

 

Now I am sorting out this blur on right side of graphics. I read maybe due to over driving video signal. Adjusting the gain pot on the video amplifier board doesnt help any. The problem got worse going from one transistor to two transistor composite board. Is it true these light 4 switchers are finicky with composite mods?

 

20200428_111516.thumb.jpg.a387fe89e553bad9167f50dfabcd0ef0.jpg

 

20200428_111853.thumb.jpg.a7c91156a0138e710d3639189fe9c2bd.jpg

 

 

Link to comment
Share on other sites

13 minutes ago, eizner23 said:

I found an old heavy 9v 1A linksys wall adapter that is working fine, the power issue is sorted out thanks everyone for the help.

I'm glad you have persevered, so far.  The bonus with the 1A over the 500mA is the display is brighter.  Some people add a mod and say the display is dull, not the case when you increase the current to compensate.

 

16 minutes ago, eizner23 said:

Is it true these light 4 switchers are finicky with composite mods?

Yeah, they seem to get a bad wrap on that front.  My Vader is still my favourite though.

 

14 minutes ago, eizner23 said:

Now I am sorting out this blur on right side of graphics.

That looks more like a local distortion affecting the TV, as opposed to the quality of the output from the VCS.  It's another case of elimination until we're left with our suspect, if you're willing to play along...

 

If there is anything electrical nearby to that area could you try moving it (especially nearby cables).  If you are able to try your VCS on a different display please try it to eliminate the VCS as having issues, which I'm hoping it's innocent.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...