My 7800 won't power on

[TerryMasters]

Hi everyone. I'm Terry Masters, and I'm hoping you guys can help me get my 7800 working again. For some reason it doesn't want to power up. I tried the original Atari power cable, and I just finished testing it with a 9v Genesis cable too but neither managed to get it to come on. When a 7800 doesn't turn on, and it's not the power cable, what could it be? I get the feeling someone shoved a third party cord in here at some point and damaged it, but I don't know where to look.

 

Thanks in advance guys,

-TM

[TerryMasters]

I took some pics of the board, incase it helps:

 

[+Mitch]

Could be the power button or voltage regulator. Do you have a volt meter or multi-meter?

 

Mitch

[TerryMasters]

Could be the power button or voltage regulator. Do you have a volt meter or multi-meter?

 

Mitch

 

Well I heard about the people having problems with the power button, but even swapping buttons didn't get it to come on. I do have a multimeter, where is the voltage regulator located?

Edited May 29, 2010 by Terry Masters

[+Mitch]

The voltage regulator is attached to the large heat-sink at the back of the board behind the cart slot. Put the ground probe of your multi-meter on the middle leg of the voltage regulator and report back on what the other two legs meter at.

 

Mitch

[+thegoldenband]

Bumping this thread because I have a similar problem. I bought my first 7800 recently, it came without a working power cord, I ordered one from Atariguide.com as recommended in the FAQ, and my 7800 won't turn on.

 

I've opened up the 7800 and tried following Mitch's instructions above. Assuming the voltage regulator is right at the top edge of the board, right below the nut used to attach the heatsink (?) and about 1/2" from being dead-center above the cart slot, then I'm getting nothing from it.

 

However, when I use my multimeter on the thingie (transistor?) marked MJE210, right between the power jack and heat sink, then I get a strong 11-12V reading. Furthermore, if I inadvertently bridge the center pin with either of the other two, the LED at the power light immediately comes on. I hope I'm not harming anything by doing that.

 

What steps should I take next? I don't have any soldering stuff, but I do have my multimeter at least. One other data point is that this 7800 originally came with a power cord from which the custom connector had been removed, leaving two bare wires. Maybe that offers some clue as to the previous owner's actions?

Edited September 1, 2011 by thegoldenband

[+thegoldenband]

Whoa, update: when I bridge two pins on MJE210, the console boots! Karateka's there on my CRT, behaving normally as far as I can tell. What am I bypassing by doing this, and what does it mean for a fix?

 

EDIT: Even stranger, I managed to get the console to stay on without a bridge for a while. I'm not sure what I did, but I tried pressing all four of the buttons (power/pause/select/reset), all of which seemed to have the expected results except power, and ultimately it stayed on -- but I couldn't get it to turn off with the power button. Then when I cut power and tried again, it was back to requiring the bridge.

Edited September 1, 2011 by thegoldenband

[+Mitch]

Sounds like your power switch may be shot.

 

Mitch

[+thegoldenband]

Yep, that's it. I just tried applying some extra pressure to the switch, and the console powered on. I feel foolish for not trying that before!

 

Other than desoldering the current switch and soldering in a new one, is there anything else I can do to temporarily improve it? Also, can I leave the upper RF shield off?

Edited September 1, 2011 by thegoldenband

[lulrik]

Hello, I'm sorry to bring this topic and I apologize in advance for my bad English with mistakes, I'm French.
I bought an Atari 7800 but it will not turn on, the LED does not work.
The power seems to work, but gives 12 volts instead of 9 volts
I tried to see if the ON switch was not HS. With an ohmmeter, I saw that the current pass when I pressed the button.
I have a mutlimétre and I heard the controller, can you give me the values ​​that I should measure about 3 pasta?

Thank you in advance

 

 

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I posted also in case your french translator would be better quality than I

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Bonjour, je suis désolé de mener ce topic et je m'excuse d'avance pour mon mauvais anglais avec des erreurs, je suis français.
J'ai acheté une Atari 7800 mais elle refuse de s'allumer, la LED ne fonctionne pas.
L'alimentation semble fonctionner, mais donne 12 volts au lieu de 9 volts
J'ai essayé de voir si l'interrupteur ON n'était pas HS. Avec un ohmmètre, j'ai vu que le courant passer quand j'appuyais sur le bouton.
Je possède un mutlimétre et j'ai entendu parler du régulateur, pouvez-vous me donner les valeurs que je doit mesurer sur les 3 pâtes ?

Merci d'avance

[+Stephen Moss]

Whoa, update: when I bridge two pins on MJE210, the console boots! Karateka's there on my CRT, behaving normally as far as I can tell. What am I bypassing by doing this, and what does it mean for a fix?

Shorting the Collector and Emitter of the MJE210 connected the power just connects the raw power to the internal 5V regulator (see circuit diagram http://atariage.com/7800/archives/schematics_pal/Schematic_7800_PAL_UL_Low.html ).

The problem is either...

Q10 (MJE210) is open circuit.

Q9 (2N3904) which is used to turn on Q10 is open circuit or there is a problem with the power on/off latching circuit comprised of U10 (4013) and associated components.

 

Check power on/off latch:

If you can locate pin 1 of U10 (or R45) measure the voltage at this point, you should get 0V when the 7800 is in its off state and about 5V when the 7800 unit is in its on state.

If you consistently get a reading of 0V then there is a problem with the Latching circuit, if you get a steady 5V when the power switch is pressed to turn the unit on then the problem is probably with Q9 or Q10.

 

Check Q9 & Q10:

If the power on/off latch appears to be working then locate R55. With the output from pin 1 of U10 at 5V (7800 on state) place one probe of a meter on each end of R55 to measure the voltage drop across it.

If you get a reading of around 9V then Q9 is OK and the problem is Q10.

If you get a reading of around 0V then Q9 is the problem so replace Q9 (re-perform this check if the 7800 still does not power on as Q10 may also be OS).

 

 

The power seems to work, but gives 12 volts instead of 9 volts

The typical type of supply used is unregulated, therefore it is not unusual for the output voltage to read about 12V when not under load, only when the 7800 is drawing current will this voltage be pulled down to something close to the specified 9 volts - they are designed to work this way.

[lulrik]

I do not understand if you have responded to my problem or the problem of "thegoldenband" (I apologize again for my difficulty in English)

My atari does not light up and nothing happens
it means that I have to do your method: "Check power on / off latch"?

 

thank you

[lulrik]

this is what I measure the transistor glued to the heatsink, values ​​its good?

 

 

 

cool or not cool ?

[yell0w_lantern]

That is a 5V regulator. It converts your power adapter voltage down to 5V. The voltage coming in should be close to what your power adapter reads alone and your voltage out should be 5. From what I have been told, you should not be off by more than about 10%. You need a 7805 voltage regulator. This explains it: http://books.google.com/books?id=bGEbLt1C168C&pg=PA232&lpg=PA232&dq=atari+7800+5v+regulator&source=bl&ots=kNjQcH-ixk&sig=FpfkwRWkeuNsXhNq9Hcknh2X4zE&hl=en&sa=X&ei=F2WaU8ezMNKNyASnzIDoCw&ved=0CCIQ6AEwAA#v=onepage&q=atari%207800%205v%20regulator&f=false

 

You may want to trace the voltage further up toward the power jack to make sure the problem is the power regulator. I have heard it is also a good idea to replace the 4 tactile switches even if they work. The switches are 12mm by 12mm with a height of about 4.3mm http://www.digikey.com/product-detail/en/PTS125SK43%20LFS/CKN9139-ND/1146894

Edited June 13, 2014 by yell0w_lantern

[+Stephen Moss]

I do not understand if you have responded to my problem or the problem of "thegoldenband" (I apologize again for my difficulty in English)

Both

Tous les deux.

My atari does not light up and nothing happens

it means that I have to do your method: "Check power on / off latch"?

 

thank you

Yes, as in both cases it would appear that the 7800 is not powering on. There should be silk screen writing (normally white) on the top side of the PCB to indicate the component reference numbers i.e. R10, U4, C12.

 

Oui, comme dans les deux cas, il semblerait que la 7800 n'est pas allumé. Il devrait y avoir écrit de sérigraphie (normalement blanc) sur le dessus de la PCB pour indiquer les composant numéros de référence c'est-à-dire R10, U4, C12.

[lulrik]

Hello and thank you all

 

 

You need a 7805 voltage regulator

 

 

So I should replace my regulator in first or Q9 and Q10 in first ?

 

If he can go? http://fr.farnell.com/fairchild-semiconductor/lm7805ct/regulateur-5-0v-7805-to-220-3/dp/1102157

costs america europe port is expensive so I try to find near my home

 

----

 

 

replace the 4 tactile switches

I noticed just now that I had my 5 volts S1 button (ON OFF switch)
button works fine since I removed and tested

 

You may want to trace the voltage further up toward the power jack to make sure the problem is the power regulator.

 

The power jack ? it ? :

 

I checked with my voltmeter on the solder on the motherboard and I have around 12 volts

 

 

Yes, as in both cases it would appear that the 7800 is not powering on. There should be silk screen writing (normally white) on the top side of the PCB to indicate the component reference numbers i.e. R10, U4, C12.

 

I can't find R10, U4, C12. there is a problem with them?

 

thank you for all your effort it must not be pleasant to work with a guy who has nothing, I'm sorry

[yell0w_lantern]

You are not seeing the silk screen designations because they are under the components.

[lulrik]

I agree with you ^ ^ but you know them by heart?

 

Can you help me?

 

 

 

thank you hugely time you have for me! You are my last opportunity

 

[lulrik]

I am very silly! I like that: thegoldenband is a bridge Q11 and LED lights!

 

 

Yep, that's it. I just tried applying some extra pressure to the switch, and the console powered on. I feel foolish for not trying that before!

Other than desoldering the current switch and soldering in a new one, is there anything else I can do to temporarily improve it? Also, can I leave the upper RF shield off?

 

What do you recommend doing? I do not quite understand: s

Change switch?
or
Change Q11?
or

other things?

 

thank you for your answers

 

[yell0w_lantern]

You have a different revision motherboard than mine. If you can't identify components to test Q10 like Stephen Moss suggested, then you could try just replacing some parts and see if that works. I am not familiar with part costs outside the USA but I would think they would still be relatively cheap.

 

Replace the four tactile switches, Q9, Q10, and the 5V regulator. It is not very precise but should fix whatever is the problem.

 

12mm x 12mm x 4.3mm spst through hole tactile switches

Q9 (2N3904)

Q10 (MJE210)

7805 voltage regulator

 

 

This should be cheaper than replacing chips.

[+Stephen Moss]

 

I agree with you ^ ^ but you know them by heart?

 

Can you help me?

 

 

 

thank you hugely time you have for me! You are my last opportunity

 

 

 

Those voltages are partially helpful but it would help to know the state of Pin 1 of the 4013 (U 10) at the time and if the brown cylindrical component is the Zener diode or not.

I think it may be the Zenner as it look like there might be an Anode indication band on one end but usually the band is easier to see than that, the colour along with a lack of voltage across it may indicate it has burnt out, possibly taking R53 with it, does it and any other component look/smell burnt? Try measuring its resistance with the leads both ways round, if it measure the same both ways you have a problem.

 

If it has burnt out that could explain why the 7800 does not turn on as the Zenner and R53 provide the 5V supply for the power on/off latch circuit, without power to this circuit Q9 and therefore Q10 will not turn on. If have some time next week I may dig my 7800 out of storage and take a look.

 

 

Replace the four tactile switches, Q9, Q10, and the 5V regulator. It is not very precise but should fix whatever is the problem.

 

12mm x 12mm x 4.3mm spst through hole tactile switches

 

This should be cheaper than replacing chips.

 

A 4013 should not be more than £0.50.

 

I am not sure what you mean by the term "tactile". Generally "tactile" would be used for a switch that provides some for of feedback (via sound or feel), at least it would in the UK. Although the switches used may have changed over time those shown in the circuit diagram here on AA appear to be the following types...

Difficulty switches = Single Pole Double Throw (SPDT)

Power, Select, Pause and Reset = Double Pole Single Throw (DPST) "Momentary" switches, in that when you press and release them they return to their original position instead of staying down and requiring a second press to return to the up position which would be called "Latching"

 

@ lulrik, if ordering from Farnell check the delivery cost as it may cost more than the components. I am not sure about France however, as I recall in the UK it is £5.00 for orders under £30.00 excluding tax, free for those above £30.00

Edited June 17, 2014 by Stephen Moss

[lulrik]

 

@ lulrik, if ordering from Farnell check the delivery cost as it may cost more than the components. I am not sure about France however, as I recall in the UK it is £5.00 for orders under £30.00 excluding tax, free for those above £30.00

Yes thank you, I saw

 

 

You have a different revision motherboard than mine

 

Yes in my mother board, Q11 is (MJE210) and Q10 (2N3904) This is surely the PAL Version I have a SCART socket.

 

 

12mm x 12mm x 4.3mm spst through hole tactile switches

I'm sure my button works, I tested

 

 

I take it?

 

I have a choice between them, the others are in USA am € 18 postage

 

MJE210 :

http://fr.farnell.com/multicomp/bd238/transistor-pnp-to-126/dp/1574355

http://fr.farnell.com/multicomp/bd438/transistor-pnp-to-126/dp/1574357

2N3904 :

http://fr.farnell.com/multicomp/2n3904/transistor-npn-to-92/dp/1574370

http://fr.farnell.com/fairchild-semiconductor/2n3904/transistor-npn-to-92/dp/9846743

http://fr.farnell.com/fairchild-semiconductor/2n3904bu/transistor-npn-40v-200ma-to-92/dp/1700648

 

LM7805 :

http://fr.farnell.com/fairchild-semiconductor/lm7805ct/regulateur-5-0v-7805-to-220-3/dp/1102157

I take that?

http://fr.farnell.com/jsp/search/browse.jsp;jsessionid=T4D5T0VZMZVJGCQLCIPJLTQ?N=0&Ntk=gensearch&Ntt=LM7805&Ntx=mode+matchallpartial&exposeLevel2Refinement=true&suggestions=false&ref=globalsearch&_requestid=68274

 

Button :

http://fr.farnell.com/wurth-elektronik/430456043736/switch-360gf-12x12mm-4-3mm-act/dp/2065138

 

 

helpful but it would help to know the state of Pin 1 of the 4013 (U 10)

I can't find 4013 (U10)

I do not see any component with 6 legs like the schematic on my motherboard

 

 

the brown cylindrical component is the Zener diode or not.

 

the first component of the right 9v electric outlet? how would I know if the zener diode?

 

I can test the transistor Q9 and Q10 and regulator and the other with : on my multimeters

 

really thank you

[yell0w_lantern]

According to Brad at Best Electronics, the place that bought out the old Atari stock, all those switches go bad eventually. Since you have it open you may as well do it.

 

And it is not my terminology, the electronics distributors here call small momentary switches meant to be triggered by a finger directly or through a plunger cap, tactile switches.

[+Stephen Moss]

lulrik,

 

Re: Replacement for the MJE210

The http://fr.farnell.com/multicomp/bd238/transistor-pnp-to-126/dp/1574355 you selected will be OK.

Towers Transistor selector also suggests http://fr.farnell.com/multicomp/2n4920/transistor-pnp-1a-80v-to126/dp/1862515 although there may be others as my copy of Towers is quite old.

There is also the MJE210G - this is the lead free version of the MJE210

 

Re: Replacement for the 2N3904

Any of the replacements you listed should be OK, Towers also suggests BC349B as a suitable replacement.

 

Re: Replacement for the LM7805CT

The http://fr.farnell.com/fairchild-semiconductor/lm7805ct/regulateur-5-0v-7805-to-220-3/dp/1102157 you suggested will be OK.

 

Re: 4013

The 4013 has 14 pins not 6 which is why you cannot find it as both D-type latches shown on the schematic are in the same IC, I can see how that could be confusing. The 4013 should have 4013 printed on it (hopefully there is only one of them). Pin 1 is to the left of the indent and pins are numbers sequentially in an anticlockwise direction.

With the indent furthest from you the power pins are bottom left (7, GND) and top right (14, Vcc) if you can measure 4.5 - 5.4 volts between pins 7 & 14 then the Zenner is OK.

 

Re: Zenner Diode

Your DVM has a diode test setting to the left of the Hfe setting, with your leads connected one way round you should get a reading of 800 -1200, when connected the other way around you should read infinity (1 on the left of the display), It would be best to remove it first and test it out of circuit.

 

Re: Testing Q9, Q10 and 7805 on your Multimeter:

You can use the transistor tester function of your DVM Depending for testing the MJE120 and 2N3904 but not the 7805.

You should get a Hfe reading of around 100 - 180(max) for the MJE210 and 100 - 300(max) for the 2N3904.

The only way to test the 7805 out of circuit is to connect a DC voltage between 8 and 30 to its input pin, connect its GND pin to 0V and measure the voltage on its output pin which should read 4.5 - 5.5 volts if operating correctly.

 

 

[lulrik]

with luck, I has it: D : http://fr.farnell.com/metrix/ax0503a/alimentation-stabilisee-ax503/dp/3430893

 

for our method :

 

The only way to test the 7805 out of circuit is to connect a DC voltage between 8 and 30 to its input pin, connect its GND pin to 0V and measure the voltage on its output pin which should read 4.5 - 5.5 volts if operating correctly.

 

(front view)
_____________
| |
| |
| 7805 |
| |
| |
| |
---------------------
|| || ||
|| || ||
|| || ||
|| || ||
9v GND 4.5 or 5.5v

 

my assembly is good ?

 

I unsoldered Q9, Q10 and 7805 and the Zener diode and I give new
PS: I have numerous pieces of diode detached home, how I could choose the right one?

Edited June 18, 2014 by lulrik