Jump to content
IGNORED

Black Screen No Voltage at VR1


TG_Cornholio

Recommended Posts

Hello All,

 

I recently picked up an Atari 5200 labeled no power "as-is" off Ebay, not expecting much. I installed the power mod and the system, powered on with a black screen. (using the RF RCA connector on the board.) This came with nothing just the console. So I started trying to figure it out. I downloaded the service manual and began looking for a problem. So I replaced the R57, R58. Q7, Q6..... nothing... NO voltage coming from the middle leg of Q6 which leads to VR1. Measure voltages on the chips and found odd low readings. Like 2.8V where the manual says it should be 5. One suggestion was replacing the 4050, that I did. same.  So no chips getting hot. So I jumped voltage over to the input of VR1. Now with output from VR1 I got voltages in places but still got the strange low voltages on some chips.  I ended up replacing all the transistors that I could as while I was here might as well...

 

No luck, same thing. with or without jumping voltage to VR1 input. Pulled apart the RF switch it was nasty but cleaned it and re-installed it, nothing. Now in jumping the voltage there is nothing getting HOT, and on a bench power supply it's drawing 440ma on.... Didn't have a wild short drawing high current.  So I didn't find any shorted capacitors and no open resistors just checking them all on basic continuity. Just to see if I could find an indicator of something. So I replaced the 4013 by the power switch as I had one so why not.

 

So looking back at the manual, the voltages in q1 and q2 were close to the values with old and new transistors. I replaced both VR1 and VR2 originally forgot to mention with the same outcome (didn't expect change on VR1 but would like to have just put new in there).   So I am at the block where it says Defective J1 or open point between point 1 of VR2 and point 2 of VR1 (with cartridge in)... wether a cartridge is in does not matter.  Has anyone seen this before?  I am trying to narrow it down and have read and replaced the most common components that I have seen on the 5200 or so i thought.

 

I also found something odd.... my board is an 18087 and I have found resistors installed where it is silk screened as capacitors???? In the parts list it says they are supposed to be ceramic capacitors. Is this a known miss print, the board looks original and not re-worked. C11, C9, C10, C20.... are all resistors?????  The values do not match on two of the same so that's a possible problem but I am not sure if I should just replace the resistor or take the chance at installing the correct value capacitors. I am assuming no.... but maybe others have seen this before. If anyone has any suggestions on where to go from here that would be greatly appreciated.

 

I did inspect the traces, no seen breaks, re-seated the chips, cleaned the legs, de-oxit all the sockets, switch and connectors....

 

Thanks,

..TGC

Link to comment
Share on other sites

6 hours ago, TG_Cornholio said:

I also found something odd.... my board is an 18087 and I have found resistors installed where it is silk screened as capacitors???? In the parts list it says they are supposed to be ceramic capacitors. Is this a known miss print, the board looks original and not re-worked. C11, C9, C10, C20.... are all resistors?????  The values do not match on two of the same so that's a possible problem but I am not sure if I should just replace the resistor or take the chance at installing the correct value capacitors.

While most capacitors don't use color codes there are some that do, and a color coded axial capacitor could be mistaken for a resistor.

Link to comment
Share on other sites

Not shown on radial types, but the values are the same

cap29zz.gif?fit=316%2C126

Capacitor Colour Code Table

Band Colour Digit A Digit B Multiplier D Tolerance (T) > 10pf Tolerance (T) < 10pf Temperature Coefficient (TC)
Black 0 0 x1 ± 20% ± 2.0pF  
Brown 1 1 x10 ± 1% ± 0.1pF -33×10-6
Red 2 2 x100 ± 2% ± 0.25pF -75×10-6
Orange 3 3 x1,000 ± 3%   -150×10-6
Yellow 4 4 x10,000 ± 4%   -220×10-6
Green 5 5 x100,000 ± 5% ± 0.5pF -330×10-6
Blue 6 6 x1,000,000     -470×10-6
Violet 7 7       -750×10-6
Grey 8 8 x0.01 +80%,-20%    
White 9 9 x0.1 ± 10% ± 1.0pF  
Gold     x0.1 ± 5%    
Silver     x0.01 ± 10%    

 

Capacitor Voltage Colour Code Table

Band Colour Voltage Rating (V)
Type J Type K Type L Type M Type N
Black 4 100   10 10
Brown 6 200 100 1.6  
Red 10 300 250 4 35
Orange 15 400   40  
Yellow 20 500 400 6.3 6
Green 25 600   16 15
Blue 35 700 630   20
Violet 50 800      
Grey   900   25 25
White 3 1000   2.5 3
Gold   2000      
Silver          
Link to comment
Share on other sites

Only time I've encountered the no voltage to VR1 was actually not that long ago when I ended up replacing both Q6 and Q7 (the large MJE201s). It was actually just the one at Q7 that ended up being the culprit but I didn't want to take any chances so replaced them both out. When you bypassed and manually forced voltage to VR1 were you getting a clean +5 out of it? Keep in mind that the two VRs essentially handle half the system each so they both need to be putting out good voltages.

 

Also your current reading seems low to me. With a cartridge in and working, the 5200 actually eats up close to 700mA from what I've seen on my bench power supply.

 

Also as was stated, Atari actually used a crap ton of ceramic banded capacitors in their consoles. They are usually green in color with the colored bands indicating their values so they can be mistaken for resistors but... they are a caps. You will also see cap silkscreens on the boards that look like they have diodes installed into them. Those are also caps. They are actually SMD caps encapsulated in glass like a standard axial component so if you aren't aware of that, be on the lookout for those as well.

 

Basically just have to keep tracing where the power goes and go from there. On average you should normally have about 11 - 12v off those higher wattage resistors behind the MJEs if that also helps.

 

Link to comment
Share on other sites

Thank you for the information, yeah I have never encountered the banded capacitors and the glass capacitors either.  I have been picking away at it. I am trying to follow the schematic and run across the component that's open or failed. Having quite the time with that.. Yes the Voltage regulators are new but even with the old one when I jumped power over to the input  of VR1 I was getting 5V out. I had one cap at C47 that when seeing if it was shorted by using continuity. It would sound and slowly trail off to nothing... It was the only cap that had that behavior, so I replaced it with a same value electrolytic for the time being. (01uf 50V) The electrolytic is doing the same exact thing. lol.... No other little blue axial cap did this they all had there respective leg on power or ground with no continuity. 

 

At least I know on a working system it now draws around 700 ma.  I have checked out all your videos Crossbow, thanks for those they were very helpful.. 

 

Will look at it again today after taking a break from it something will hopefully pop up...

Link to comment
Share on other sites

  • 1 month later...

Well,

 

Had fun jumping power to chips on the original board.. no good... Got a 2nd non working board off of Ebay.... Well that was a mess someone did a bunch of stuff in there.. but now I had another board with some parts and was able to try and swap chips out... Nope..... Mmmmmmm... okay took a break..... So I decided to try again on a non working 5200 auction.... So..... Q1, Q7, Q8 and the 4013..  powered up with the a Defender cart and finally it works!.. lol..  Had to replace a controller port as it looked all bent up and pushed in... Put new regulators, MJE's, audio caps as I had them anyways...

 

Next the controller that I got, untested of course, it doesn't work... one button maybe... Took it apart and the membrane looks to have seen better days. Pulled that out and ordered a replacement membrane. Might put some copper on the carbon pads, maybe not will see if it works first. Thanks again for the assistance. :)

  • Like 1
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...