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What is this witchcraft? Heresy! 2600 switching power supply modification


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#101 hizzy OFFLINE  

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Posted Wed Sep 27, 2017 12:31 PM

Anyone try the tracopower on a modded 2600? Curious to see how S-video & composite are affected :)



#102 SiberianSpForces OFFLINE  

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Posted Thu Sep 28, 2017 7:15 AM

In short, for the 2600, the TSR 1-2450 will run cooler and give a better picture with no audio issues? For the Intellivision, from what I seen, uses less power but doesn't improve picture?

#103 nick3092 OFFLINE  

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Posted Thu Sep 28, 2017 4:32 PM

Someone asked earlier in the thread to put one of these buck converters up against a 7508 on a scope.  I have access to all 3 of these things, but I admit I'm not all that great with using a scope.  So I may not have totally valid pictures here.  But if someone else can tell me exactly how to set the scope up, I can repeat these tests.

 

I used a Sega Genesis 2 2103 10vdc to power the test.  I used two 20 ohm resistors in parallel for a 10ohm load on the regulator to approximate a 500ma draw.  The buck converter I have on hand is the OKI 78SR-5 that I believe someone had also linked to earlier.  I left the vertical and horizontal settings the same on both tests.  That is what gave me the best image on the buck converter (which I tested first), but it doesn't look like it gave anything very usable on the linear screen shot.

 

Here is the buck converter:

DS1Z_QuickPrint1.png

 

 

Here is the linear 7805:

DS1Z_QuickPrint2.png

 

Let me know if anyone wants me to rerun this test with different settings on the scope.



#104 Osgeld OFFLINE  

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Posted Thu Sep 28, 2017 5:17 PM

12mhz  with a nice spike at each zero crossing at some much higher frequency

 

I dont know the pixel clock on the genesis but the noise is pretty close to a function of the 3.57xxxxxxxx color burst, anyway interesting



#105 Kosmic Stardust OFFLINE  

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Posted Thu Sep 28, 2017 6:04 PM

Now put a filter cap across the load (which the console already does) and watch the ripples go away...

A very small air coil inductor (a few loops of enameled wire will do) in series with the load might also help suppress ripples at the risk of transients with sudden load changes. You could easily build a filter to eliminate the ripple.

#106 Osgeld OFFLINE  

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Posted Thu Sep 28, 2017 6:16 PM

Now put a filter cap across the load (which the console already does) and watch the ripples go away...

A very small air coil inductor (a few loops of enameled wire will do) in series with the load might also help suppress ripples at the risk of transients with sudden load changes. You could easily build a filter to eliminate the ripple.

 

 

which makes you wonder why they didnt just do that in the first place ... i mean for the price of the durn things 


Edited by Osgeld, Thu Sep 28, 2017 6:17 PM.


#107 nick3092 OFFLINE  

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Posted Thu Sep 28, 2017 7:24 PM

I dont know if I have a 2200uf handy (to simulate the 2600 filter) to retest the buck converter. But Im fairly certain I have two 1000uf caps handy I could parallel. Ill check my stock and retest this weekend.

#108 Osgeld OFFLINE  

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Posted Thu Sep 28, 2017 8:02 PM

a 1000 uf will get rid of the big waves easily heck I bet a 100 would , the high frequency stuff which is going to mess with the video signal (on a genesis as stated earlier in this thread) is going to need something like a 150-200pf in parallel (doing off the top of my head guess maf) 

 

all caps resist changes to voltages

 

big caps resist slow changes 

 

small caps resist fast changes 


Edited by Osgeld, Thu Sep 28, 2017 8:02 PM.


#109 Keatah OFFLINE  

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Posted Thu Sep 28, 2017 8:58 PM

which makes you wonder why they didnt just do that in the first place ... i mean for the price of the durn things 

 

Well maybe it all works fine when new. And the design life of the VCS couldn't have been more than a couple of years. So when this sort of noise creeps into the circuit from old age, it'll show. If it was designed for long life, I'd suspect a whole different style of power supply would've been used.



#110 Osgeld OFFLINE  

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Posted Thu Sep 28, 2017 9:46 PM

 

Well maybe it all works fine when new. And the design life of the VCS couldn't have been more than a couple of years. So when this sort of noise creeps into the circuit from old age, it'll show. If it was designed for long life, I'd suspect a whole different style of power supply would've been used.

 

talking about the 8$ SM 780x replacement voltage regulators not the VCS, every one I have ever used or looked at is as noisy as a pirate AM station 

 

it depends on the application and the exact model, for the most part for quick n dirty low or no heat its fine, I used one on my atari 400 computer ... I also used one on a xmega micro controller clocked at 32 mhz and all hell broke loose

 

generic fix all's wont work in all situations


Edited by Osgeld, Thu Sep 28, 2017 9:51 PM.


#111 nick3092 OFFLINE  

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Posted Fri Sep 29, 2017 7:14 AM

In thinking the filtering aspect through some more, I forgot to take into account that generally the main filter cap is either built into the wall wart or installed prior to the 7805 in the console.

So me adding a large cap after the buck converter and taking a shot on the scope isnt going to be really useful in determining what one of these actually looks like in circuit of a console. At least not from a drop in replacement standpoint. It might give some idea though of what additional filtering might be needed if you make the change over to a buck converter though.

I do have a fairly good selection of film caps and some silver mica caps ranging from probably 15pf to a couple hundred pf. And random electrolytic values. If there are any scenarios people would like to see, I can set it up and take a screen shot. I know there was a suggestion to try 150-200pf. Im pretty sure I have a mica in that range I could try.

#112 nick3092 OFFLINE  

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Posted Fri Sep 29, 2017 4:12 PM

I repeated the test today, although with a slightly different load and I zoomed in one more on the horizontal scale.  Yesterday I didn't run the wattage calculation on my dummy load of two 1 watt 20 ohm resistors in parallel at 5v.  But today I noticed the resistors were quite hot.  When I ran the numbers today, it came out to about 2.5w of power.  So each 1w resistor was cooking a little at 1.25w.  So to be safe I used three 33 ohm 1 watt resistors in parallel for an 11 ohm dummy load.  That cut the current down to 450ma, and spread the heat out better on the resistors.

 

Anyway, here us the raw picture again.  But this time slightly zoomed in more and with the new 11ohm load.

DS1Z_QuickPrint8.png

 

And here is a 300pf silver mica.  It is kind of hard to tell, but the only change is the zero crossing spike got slightly larger.  I also tried a .01uF and .1uF film, and they basically did the same thing as the 330pf - just a slightly larger spike at zero crossing.

DS1Z_QuickPrint10.png

 

And for grins, here is a 2200uF.  It noticeably cut down the ripple.  But the zero crossing spikes were largely unchanged.  Maybe just a touch larger, but not by much.

DS1Z_QuickPrint9.png


Edited by nick3092, Fri Sep 29, 2017 4:13 PM.


#113 Osgeld OFFLINE  

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Posted Fri Sep 29, 2017 5:43 PM

yea filtering out noises in the mhz range doesnt leave a lot of wiggle room in capacitor sizes, at my work we have to deal with it all the time due to industry requirements (automotive), and its often we send something up for pre-emc (before spending the money on the real deal certified lab test) and almost the very next day one of our butts is on a flight with a cap kit in the luggage 



#114 Kosmic Stardust OFFLINE  

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Posted Sat Sep 30, 2017 10:13 AM

...and almost the very next day one of our butts is on a flight with a cap kit in the luggage

Wow human transport. You must really need those parts fast. Fedex overnight is generally cheaper than round trip air fair btw. For shipping parts, not suggesting you attempt to send people that way. :P

#115 Osgeld OFFLINE  

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Posted Sat Sep 30, 2017 10:15 AM

well aint nobody going to fix it for us lol



#116 Kosmic Stardust OFFLINE  

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Posted Sun Oct 1, 2017 12:13 AM

lol. :P




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