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PAL Vader Comp. Mod getting scrolling interference? (pics) IDEAS/HELP?


Microswitch

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Greetings All...

 

Been a lurker for a while and finally got myself some REAL hardware instead of using emulators.

 

I've been dying to play my all time favourite Atari 2600 games... Kung Fu Master, HERO, River Raid, Gravitar!

 

Anyway, I got a nice clean Vader (Pal) console with no power supply. Bought a new power supply and new components for a basic composite video mod.

 

All went well and I'm really happy with the sound, colours and clarity of the image EXCEPT I get some kind of horizontal interference pattern that slowly scrolls upwards? I've tried multiple TV's and even ran it through a PVR/DVD's A/V input... exactly the same problem. I'd love to hear if anyone has experienced this before and what worked for them regarding a fix.

 

Pictures and further details below (my 1st post so apologies if I'm doing anything dumb):

 

post-45382-0-46402200-1455212969_thumb.jpgpost-45382-0-18991100-1455212999_thumb.jpgpost-45382-0-48422500-1455213017_thumb.jpgpost-45382-0-85749000-1455213037_thumb.jpg

 

BASIC MOD:

 

http://mrpjevans.com/2014/05/composite-modding-the-atari-2600/

 

PARTS USED:

  • 1 x 2N3904 Transistor
  • 1 x 3.3K Resistor
  • 1 x 2.2K Resistor

PARTS I REMOVED:

  • RF BOX
  • R222
  • R209
  • C209
  • Q201 (three-pin)
  • Q202 (tall red plastic thing)

MY AMATEUR ELECTRONICS THOUGHTS:

- Power related interference replace caps (all?)
- Somehow shield the video signal cable on my mod

- Voltage regulator (read somewhere that they almost always need replacing)
- Bad TIA...I really hope it isn't this :(

Edited by Microswitch
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Unfortunately it's likely a bad TIA. But there's no way of knowing for sure unless you stick a replacement TIA into your console OR take the TIA out of your console and test it in a known working console.

Other problems that it could be is...

Dirty Color Pot (clean with rubbing alcohol)
Bad Chrominance crystal (incredibly unlikely)
Lack of a bypass cap on the VB amplifier (I believe the cap is C209? Might be C219)

----------------------

EDIT: I just realized that your image looks similar to a couple of Atari A/V mods I've done in the past. The problem was a cold solder-joint somewhere on the A/V hack. Try reflowing the connections between the two resistors, the wires that connect to the 2600, and the 2N3904.

Edited by SwampFox56
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I don't think there's anything wrong with your system. I bet anything it's that cheap Chinese switch mode power supply your using that's causing that interference. Those cheap Chinese supplies almost never have any EMI/RFI filtering components to reduce on manufacturing cost. What you need to use is a class 2 power transformer.

Edited by thecrypticodor
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Well I remade the little AV circuit, spacing the parts further apart and gave the colour pot a blast of compressed air, and re-soldered the video to the main board but the end result is exactly the same. :?

DOHuCKU.jpg

 

I don't think there's anything wrong with your system. I bet anything it's that cheap Chinese switch mode power supply your using that's causing that interference. Those cheap Chinese supplies almost never have any EMI/RFI filtering components to reduce on manufacturing cost. What you need to use is a class 2 power transformer.

 

That would be an easy fix, I hope it's just the power supply. This is the seller I got it from... seems like a semi professional guy with good feedback, I'll ask if he has the specifications of the power supply:

 

http://www.ebay.com.au/itm/131452642606

Edited by Microswitch
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Almost none of those no name china switch mode power supplies have any interference reduction components. People buy these kind of supplies from china for little over a dollar and than resell them as console specific supplies. For instance I can buy any 9V 1A supply with the correct plug and polarity and and re-sell it as a Sega Master System supply.

 

The thing is if you were using the original RF you wouldn't have a problem using that supply. RF modulators usually have interference reduction components such as chokes or inductors that would filter out that noise.

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I bet anything it's that cheap Chinese switch mode power supply your using that's causing that interference.

 

SOLVED! Thank you so much! :-D:thumbsup:

 

Wow how frustrating, I wonder how many Atari newbs out there get a system, AV mod it and have the exact same problem after buying a new power supply off eBay... I bet many (otherwise good) Atari's end up in the bin this way. :_(

 

I used an old cordless phone power supply I had and got a near PERFECT image:

 

Panasonic KX-TCA1AL Australian AC Adapter 9VDC 350mA for KX-TCA256 phone (Note: I had to switch tips and reverse the polarity)

$_75.JPG

 

I should also mention that this power supply is not regulated, which is why I'll be replacing the 35 year old voltage regulator in the console before playing anything.

Edited by Microswitch
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  • 3 weeks later...

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