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Help, Atari 400 with no power!

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I want to fix my 400 that has no power, it has been sitting for a while now and I have tested the power supplies I have and they are fine. Can I change a fuse or a chip to get this working? Any tips would be greatly appreciated as there doesn't seem to be any repair guides on line that I can find.

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The 400/800 don't have an internal fuse, it's in the power supply.

 

There are many things it could be, either power switch(there's one for the cartridge door as well as the one on the right side), power jack, rectifier diodes, voltage regulators, bad solder joint, etc.

 

Here's a link to the 400/800 Field Service Manual

http://www.atarimania.com/documents/Atari_400_800_Field_Service_Manual_June_82.pdf

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Bill is correct. But the most likely answer would be replace the ram card and or CPU card, then power board, then check IC's. if you have it apart, you might as well put a 48k ram card in it.

Edited by Paul Westphal

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Just hijacking this necro thread as my 400 has the same issue.

I just got it (it was sold as non-working, so not surprised) a couple of days ago and JUST got the PSU an hour ago, and then tried my first power up.

Unfortunately I can't do any real testing yet, as we have family over, but I did sneak into my office to plug it in for a quick test.

I'm cautiously optimistic about my first test because there is zero indication of life.  No LED, no nothing...

I did make sure the cart door switch was down.  I could hear it click.  But nothing.

 

So I am hoping that might mean there is something in the power supply circuitry (diodes, etc) or the switches that is keeping it from working.

 

I love having this particular family over, but I really wish I could start tearing this thing apart right now...  ;-)

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2 minutes ago, desiv said:

Just hijacking this necro thread as my 400 has the same issue.

I just got it (it was sold as non-working, so not surprised) a couple of days ago and JUST got the PSU an hour ago, and then tried my first power up.

Unfortunately I can't do any real testing yet, as we have family over, but I did sneak into my office to plug it in for a quick test.

I'm cautiously optimistic about my first test because there is zero indication of life.  No LED, no nothing...

I did make sure the cart door switch was down.  I could hear it click.  But nothing.

 

So I am hoping that might mean there is something in the power supply circuitry (diodes, etc) or the switches that is keeping it from working.

 

I love having this particular family over, but I really wish I could start tearing this thing apart right now...  ;-)

 

Just because the door is completely shut and you heard it click, doesn't mean that anything is actually making connection to the door interlock switch. It could be something as simple as a bad door interlock switch or a broken or missing door interlock switch plunger. From there it could get more involved and technical.

 

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4 minutes ago, bfollowell said:

 

Just because the door is completely shut and you heard it click, doesn't mean that anything is actually making connection to the door interlock switch. It could be something as simple as a bad door interlock switch or a broken or missing door interlock switch plunger. From there it could get more involved and technical.

 

Exactly my point.

In my mind, those type of things are much easier to fix than things like bad CPU/RAM or other supporting chips.

I'm hoping it is something like the interlock switch!!!

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I was gifted an early 400 a couple of months ago. It also didn't power up. When I opened it, it had no plunger for the door interlock switch. I taped the switch down and it worked just fine. The keyboard ribbon cable had broken wires as well. I ordered a NOS 400 keyboard, an internal speaker and a door interlock switch plunger from Best Electronics.

 

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Just a thought, what power supply did you get, is it an Atari one, if not,  can it supply enough current ?

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21 minutes ago, TGB1718 said:

Just a thought, what power supply did you get, is it an Atari one, if not,  can it supply enough current ?

Also: it is outputting AC voltage, not DC, correct?

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yes, AC 9V is normal 

 

Not got a 400, but I think it's about 1.5A

Edited by TGB1718

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Yep, got a 9VAC 1.5A supply.

And I checked it to make sure it was AC and outputting around 9VAC before I plugged it in.

I do wonder if one of the previous owners used a DC adapter, as those are more common and if that did something to the power board?

Not sure if that would break something or just not work, but I can see someone just using the wrong PSU.

Pretty sure that's what happened (wrong polarity I would guess in that case) with my "broken" SegaCD when I got that. That one was just a fuse tho...

Hoping to be able to open the 400 tomorrow maybe and use the multimeter to see how far any of the voltages are going....

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Because there's a full wave rectifier on the input, I don't believe a DC PSU would damage it, unless it was

a lot greater than about 15V, with DC input, I don't think the -5V would be generated though

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OK, looks like I don't have a simple power problem.  ;-(

 

I have a power LED problem (among other things).

I finally go to testing and saw 5v DC in a few spots where it should be...

 

So I thought maybe the LED not showing might just be an LED issue.

I put it back mostly together, replaced the damaged RF cable that I had removed (it was cut up when I got it, had gotten pinched in something), and took it to the TV downstairs...

 

Plugged it in, turned it on, and black screen...

Still no LED light, but it goes from static to black screen...

 

Unfortunately for me, that means more involved troubleshooting (I was really hoping it was some power thing, but oh well...).

 

I did notice that twice when I powered it on, I got another color.  (Once red, and once orange), but for the most part, it is black when I turn it on...

Looks like I have a decent (I think, was using the easy-to-grab analog multimeter) 5v and 12v.  (I haven't checked for -5V yet)

So, the next steps (other than checking for -5V) are things like CPU clock, CTIA/GTIA, etc...  Things I'm not ready/equipped to troubleshoot right now...  I don't have any known good spare parts for swapping....  (I did see it was a 16K equipped 400... I didn't check for CTIA/GTIA..)

So I think I'll clean it up and set it on the shelf for now...

It is still a great looking machine to have on the shelf, and at some time I might start digging in deeper...

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On 5/18/2015 at 1:40 AM, vintagegamecrazy said:

I want to fix my 400 that has no power, it has been sitting for a while now and I have tested the power supplies I have and they are fine. Can I change a fuse or a chip to get this working? Any tips would be greatly appreciated as there doesn't seem to be any repair guides on line that I can find.

First thing I do is look at all the electrolytic caps.  Make sure that none of them are swollen or leaking.  Then I look for any blackened or burnt components.

If everything looks good, make sure that you have about 9 or 10 volts AC at the junction of CR208 and CR209 to ground (with the power switch set to ON

and the interlock switch closed).  If that voltage is good, I would suspect the voltage regulators.  A201 (78M12) and A202 (7805).  Here is a copy of the

Atari field service manual for Atari 400's and 800's.

 

DavidMil

 

Atari_400_800_Field_Service_Manual_June_82.pdf

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18 hours ago, ClausB said:

The power LED does run off -5V, and so does the RAM, so do check that next.

Good catch!

Family visiting is going, so I finally got a chance to try it again.  On J201, I am still seeing 12v (pin 2) and 5v (pins 5,6, and 7).

But pin 18 does not have -5v.

So, there is something wrong there!

 

Now I need to figure out how to test diodes in circuit.  The Field Guide is telling me to test:

CR206 - CR209

CR201-CR203

 

And C201, C202, and C210 (These are I think capacitors).

 

My digital multimeter does have a diode check function, but I haven't used it before, so not totally sure if I am doing this right.

Currently (pun intended), with no power attached and my meter in diode check mode, I am getting.

Not attached to anything, meter is showing "1."

Diode:   DIR1  -  DIR2  (tested each twice, swapping the multimeter leads)

CR201: .477    -  1.

CR203: .575    -  1.

CR202: .581    -  1.

 

CR206:  .571   -  .850

CR207:  .576   -  .844

CR208:  .575   -  .852

CR209:  .577   -  .850 

 

Haven't tested the CAPs at all, but I don't have an inline tester (I believe that is needed for CAPs).

I also haven't yet tested the LED itself.  (I think that is CR210???  It has a black plastic piece covering most of the lettering.)

 

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At times like this, I wish I understood electronics... ;-)

 

Not totally sure if a diode test in circuit is good for testing the LED, but when I did that, I got 1. on both directions.

So I am thinking the LED is dead, but not sure.   And I wouldn't think a dead LED would cause this issue.

 

I did try measuring some voltages at certain points while powered on and I got voltages on CR202 and CR203, but didn't get any voltages at CR201, the zener diode.  So that is making me wonder about him.  But I am not sure that is a valid test, as I don't really understand this...

 

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3 hours ago, desiv said:

I did try measuring some voltages at certain points while powered on and I got voltages on CR202 and CR203, but didn't get any voltages at CR201, the zener diode.  So that is making me wonder about him.  

 

No, I think now that maybe he isn't getting any/proper voltage into him maybe?

Trying to understand the power flow (and failing)...

 

Pin 18 is supposed to have -5V, but doesn't.  Tracing backwards, the traces from him go to

:The LED

:One side of CR201 (zener)

 

Assuming the LED isn't involved in the problem (broken or not)...

The (other)side of CR201 goes to the one side of CR203 (which reads nothing on my MM, the other side I can read -6.7v with my MM), the +side of C210, and GND.

 

Since I'm not sure how to properly read some of these voltages with my MM, I'm not sure what that is a sign of tho. ;-)

 

It seems like there is a close voltage around there.  -6.7v (unloaded) sounds close to me?  Tho maybe it is too high (low? being negative?) and that is keeping it from passing thru.

 

The zener should be rated at 5.1v, but I don't know if that is in play here... (Meaning I don't know how that would work with the voltages; I know it is in the circuit.. ;-)...  I am thinking that it should be taking in  the -voltage and outputting around -5.1V?? (If installed backwards?)...

I'm not seeing that -6.7V DC with my MM on either side of the zener, but I think that could just be how I am measuring (black wire on ground (RF casing), red wire on the diode)?

 

 

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You have traced it back to them, so just to be sure pull and test the diodes CR201 AND CR203, I doubt the cap is bad but you could check it to be sure... -6.7 minus the diodes voltage drop should leave you in the -5 volt range.. it would seem something may have exceeded the diodes current range and killed it.

Edited by _The Doctor__
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I made these VDC measurements on a 400 PS board unconnected to a system:

CR201 & CR210: -5.2

CR210 & R201: -6.9

R201 & C201 & CR202: -11.6

CR202 & CR203 & C202: -6.0

C202(+): +5.7

 

Hope that helps.

Edited by ClausB
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Thanx all, I ordered some diodes (not the zener yet, but probably will soon).

The markings on the diodes are a bit interesting...

I think almost all the diodes I can see are marked 1N 8124 although CR202 is marked 5391.

I see in the field guide that they were (at some point) 1N 4001s, but were recommended to be replaced with IN 5391s.

I do wonder about the 8124s, but I can't tell from the data sheets if there is any problem with the 8124s...

 

But I ordered enough 5391s that I should be able to replace the rest of them if needed...

(Not by choice per se.. It was only $1 more to get 100 of those diodes over the 25 pack.  And one or two cost almost as much as that.. ;-)

 

I supposed I'll have to find a 5V LED to possibly replace the power LED too..  Just looked through my stuff and all the LEDs I have are the smaller ones (for Arduino stuff).

 

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37 minutes ago, desiv said:

I supposed I'll have to find a 5V LED to possibly replace the power LED too..

CR210 is not a 5V LED, R201 is a 330 ohm resistor which limits current/voltage. If you use an LED with a different voltage than the original you may need to adjust the value of R201.

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1 minute ago, BillC said:

CR210 is not a 5V LED, R201 is a 330 ohm resistor which limits current/voltage. If you use an LED with a different voltage than the original you may need to adjust the value of R201.

Good I didn't order it yet.  ;-)

Do you know what type of LED (voltage) it is?

Thanx

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LED's are not a particular voltage although they do drop some voltage when they light,

can be anything between 1.2V and 2V (that's not absolute, just a guide).

 

The brightness is a product of the voltage across it and the resistor and current flowing through them, hence why @BillC  says you

may need to change the value of R201. It's current ( :) ) value of 330 Ohms suggests

there's about 10 mA flowing through the LED which sounds about right.

 

So if you know the voltage drop of the LED your fitting, subtract the from the voltage and you can calculate the 

resistor value i.e. if drop is 1.7V subtract from the 5V = 3.3V, you need 10mA so from Ohms Law

R=V/I so 3.3/.01= 330 Ohms

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