Need Atari 400 issues

[legoman31802]

Hey all I recently got an Atari 400 but when I got it home and plugged it in I just got a bunch of random characters and lines. I figured out a couple chips were the problem so I bought a new motherboard that had all the chips for $20. When I go to turn it on I see a purple screen with a curser but then it quickly fades away and now it’s back to what was on there before. I decided to check the power supply and it turns out I was given a 9.5 volt supply. Idk if that’s what is causing this or something else. Any suggestions?

[cwilbar]

Was that a 9.5V AC or 9.5V DC supply ?

 

I wouldn't think .5 volts would damage it (as that is is only 5.6% off), as the rectification, regulation, and filtering are on the inside of the Atari.

 

However, if you use a DC supply.... well, something bad could very well happen. 

 

If you are unsure, post a pic of the power supplies input/output data from it's label/case.

 

If you are lucky, any damage would be restricted to the 400's power board which is not difficult to replace (no soldering required unless you have some internal upgrades that have wires soldered to it).

 

 

[legoman31802]

3 hours ago, cwilbar said:

Was that a 9.5V AC or 9.5V DC supply ?

 

I wouldn't think .5 volts would damage it (as that is is only 5.6% off), as the rectification, regulation, and filtering are on the inside of the Atari.

 

However, if you use a DC supply.... well, something bad could very well happen. 

 

If you are unsure, post a pic of the power supplies input/output data from it's label/case.

 

If you are lucky, any damage would be restricted to the 400's power board which is not difficult to replace (no soldering required unless you have some internal upgrades that have wires soldered to it).

 

 

It says output is 9.5v AC and 40VA  And I also don’t think it would be that big of a problem but then again idk what else it could be

[cwilbar]

The 400 board with all the chips you put in....  did it come with the power board, or you moved that from the old board to the replacement board ?

 

Was the replacement board bought as tested/working ?  or unknown/as is ?

 

What other parts did you move over from your old configuration ?  CPU board and RAM board ?

 

Presuming it was ok when you assembled it, and that it is not ok now, then the only thing is power is damaging something.  And in this case, I don't think the extra .5V could do this, I woudl then suspect the power board in the 400.

 

I presume even approaching it a day later and you turn it on, the symptoms are consistent ?  It doesn't display a screen with a cursor that then fades away again ?

 

If you have it hooked up with sound, with no cartridge it would go into memo pad, and you should hear 'beeps' when you type.

 

If you start it up while holding the start button, do you get an audible sound ?  If I recall correctly you will get a cassette loading tone.

 

If you get sound out of it, that would indicate a video issue.

 

Unfortunately a failure in ANTIC/GTIA, or POKEY can wedge the whole system.  So, a non responsive system could have any chip be the failure points.

 

I'd suggest opening it up, and running it caseless.  Find the schematic and/or service manual on-line and check the voltages from the PSU to the mainboard.  Use a DVM to check them, and check AC power on the leads too to find out if there is any excessive ripple voltage on those DC lines.

 

If all the DC voltages measure fine and there is zero or close to zero AC volts on those outputs, then the AC adapter through the power supply is good, and the issue is on the mainboard, the cpu board, or the ram board.

 

 

[Sugarland]

7 hours ago, legoman31802 said:

Hey all I recently got an Atari 400 but when I got it home and plugged it in I just got a bunch of random characters and lines. I figured out a couple chips were the problem so I bought a new motherboard that had all the chips for $20. When I go to turn it on I see a purple screen with a curser but then it quickly fades away and now it’s back to what was on there before. I decided to check the power supply and it turns out I was given a 9.5 volt supply. Idk if that’s what is causing this or something else. Any suggestions?

Yes. Send it to someone who knows how to fix it. 9.5v AC is too much. Problem could be your power board (inside computer) or one of the custom chips, three of which are not on the motherboard.

[legoman31802]

8 hours ago, cwilbar said:

The 400 board with all the chips you put in....  did it come with the power board, or you moved that from the old board to the replacement board ?

 

Was the replacement board bought as tested/working ?  or unknown/as is ?

 

What other parts did you move over from your old configuration ?  CPU board and RAM board ?

 

Presuming it was ok when you assembled it, and that it is not ok now, then the only thing is power is damaging something.  And in this case, I don't think the extra .5V could do this, I woudl then suspect the power board in the 400.

 

I presume even approaching it a day later and you turn it on, the symptoms are consistent ?  It doesn't display a screen with a cursor that then fades away again ?

 

If you have it hooked up with sound, with no cartridge it would go into memo pad, and you should hear 'beeps' when you type.

 

If you start it up while holding the start button, do you get an audible sound ?  If I recall correctly you will get a cassette loading tone.

 

If you get sound out of it, that would indicate a video issue.

 

Unfortunately a failure in ANTIC/GTIA, or POKEY can wedge the whole system.  So, a non responsive system could have any chip be the failure points.

 

I'd suggest opening it up, and running it caseless.  Find the schematic and/or service manual on-line and check the voltages from the PSU to the mainboard.  Use a DVM to check them, and check AC power on the leads too to find out if there is any excessive ripple voltage on those DC lines.

 

If all the DC voltages measure fine and there is zero or close to zero AC volts on those outputs, then the AC adapter through the power supply is good, and the issue is on the mainboard, the cpu board, or the ram board.

 

 

The board was bought as tested/working and I swapped over everything except for the IC chips on the main board itself. 
 

after a day it still has the same issues and same mess on the screen. 

rhe computer tries to make sound but the speaker sounds like it is almost dead. Can barely make a beep. 
 

and I will try testing all the power stuff when I get back from school. Thank you very much for the advice!

[legoman31802]

8 hours ago, Sugarland said:

Yes. Send it to someone who knows how to fix it. 9.5v AC is too much. Problem could be your power board (inside computer) or one of the custom chips, three of which are not on the motherboard.

Who exactly should I send it to? Or what type of shop?

[TGB1718]

9 hours ago, Sugarland said:

Send it to someone who knows how to fix it. 9.5v AC is too much.

Don't send it anywhere, nothing wrong with it, just measured my 800 PSU, it's 10.48V AC off load.

and you can't fix these unless there's no output voltage, all it is , is a step down transformer.

 

Quote

9.5v AC is too much.

No it's not, this is the RMS AC voltage before rectification and regulation, the regulators are 7805 and 7812

both can take an input voltage of 35V max, the dc voltage from the rectifiers will be around 13.4Vdc before regulation,

well within spec of the regulators.

 

I would be looking to check the regulated DC voltages after regulation inside the 400.

 

Check the 2 +5VDC (A and B), the +12VDC and the -5VDC

 

Edited August 18, 2020 by TGB1718

[legoman31802]

28 minutes ago, TGB1718 said:

Don't send it anywhere, nothing wrong with it, just measured my 800 PSU, it's 10.48V AC off load.

and you can't fix these unless there's no output voltage, all it is , is a step down transformer.

 

No it's not, this is the RMS AC voltage before rectification and regulation, the regulators are 7805 and 7812

both can take an input voltage of 35V max, the dc voltage from the rectifiers will be around 13.4Vdc before regulation,

well within spec of the regulators.

 

I would be looking to check the regulated DC voltages after regulation inside the 400.

 

Check the 2 +5VDC (A and B), the +12VDC and the -5VDC

 

When you say power supply do you mean the power board inside the computer or open the actual external power supply?

[TGB1718]

Just now, legoman31802 said:

When you say power supply do you mean the power board inside the computer or open the actual external power supply?

The power supply inside the 400 as shown in the above diagram, as I said before, there is nothing in the external power supply

other than a step down transformer and maybe a fuse, that's all, if you're getting 9.5VAC then it's probably ok.

[mimo]

when you say you replaced the motherboard, did that include the CPU board? this has GTIA and ANTIC and the CPU onboard, if you have not changed this then you will likely just replicate the issue with the new motherboard , could you maybe upload some pictures/video to show what you have changed and what you are seeing display wise 

Edited August 18, 2020 by mimo

[BillC]

On 8/17/2020 at 3:12 PM, cwilbar said:

Was that a 9.5V AC or 9.5V DC supply ?

 

I wouldn't think .5 volts would damage it (as that is is only 5.6% off), as the rectification, regulation, and filtering are on the inside of the Atari.

 

A 9.5VDC power supply would not supply any power for the -5VDC rail and the voltage doubler circuit for the +12VDC rail would also not work. Both of these voltages are required by the DRAM chips used in the original 400/800 8/16kB memory cards.

Edited August 19, 2020 by BillC

[TGB1718]

6 hours ago, BillC said:

A 9.5VDC power supply would not supply any power for the -5VDC rail

He already said it's an AC power supply

 

On 8/18/2020 at 2:42 AM, legoman31802 said:

It says output is 9.5v AC and 40VA  

 

[xrbrevin]

6 hours ago, BillC said:

A 9.5VDC power supply would not supply any power for the -5VDC rail and the voltage doubler circuit for the +12VDC rail would also not work. Both of these voltages are required by the DRAM chips used in the original 400/800 8/16kB memory cards.

this is why the 400 and 800 have an internal power board.

Edited August 19, 2020 by xrbrevin
typo

[BillC]

2 hours ago, xrbrevin said:

this is why the 400 and 800 have an internal power board.

The internal power board requires AC for the -5VDC and voltage doubler circuits to work. Even if the power supply delivered high enough DC voltage to eliminate the need for the voltage doubler circuit it would still not be able to supply -5VDC.

[xrbrevin]

ah apologies, i misread your post. i thought you were referring to his AC power supply, not a theoretical DC one

[legoman31802]

Hope this helps y’all. I am bad at explaining stuff. Sorry. Also excuse the mess I have a lot of projects going at once.

Edited August 19, 2020 by legoman31802
Video didn't upload right

[ClausB]

Looks like a 3rd-party 32K RAM board in there. Do you have another RAM board to try? If not, you can try swapping around the RAM chips.

 

Also, what is that black box the motherboard is resting on? Is the top made of metal or plastic?

 

Edited August 19, 2020 by ClausB

[legoman31802]

47 minutes ago, ClausB said:

Looks like a 3rd-party 32K RAM board in there. Do you have another RAM board to try? If not, you can try swapping around the RAM chips.

 

Also, what is that black box the motherboard is resting on? Is the top made of metal or plastic?

 

It’s an Xbox 360 so it’s plastic. And I’ll give that a try when I get home 

[Sugarland]

The problem with putting good parts in a non working machine is the risk of breaking the good parts. For example if the power board is bad it could ruin the motherboard. We don't know yet if that's happened and even if so, please don't throw anything away as it could be good.  Last year I got a 400 from someone who could not get it working. I noticed in the auction that it was a PAL machine which does not work on NTSC displays. However I see that sometimes your image stabilizes which a PAL machine would not stabilize afaik.  Does it have a DOM sticker in the cart slot area? If it says PAL then it will not work on an NTSC TV. 

 

Edit: I concur with ClausB that the RAM is suspect, but you said you replaced it.  ?‍♂️

Edited August 19, 2020 by Sugarland

[ClausB]

Agreed. Step one of troubleshooting is really a measurement of all power supply voltages. DVMs are cheap.

[thax]

Hello to you all! I haven't been on here for near ten years and I'm glad to be back! Some nice 400 conversations going on, I tried to start a new conversation but there wasn't anything in the pull down menu to do with the topic so anyway - more 400 problems.

 

I recently acquired a 400, in one piece but it was dead. 

First thing I did was check the internal psu, when I activated it one of the diodes threw out sparks so I replaced all the diodes and the caps were rough too so just replaced them. Thought it best as one of the axial caps was leaking and another one you could easily spin round on its pins!

Also replaced the regs and power restored.

Tested voltages, 5v and 12v all good.

Fired it up and just get a normal blue screen with the white cursor in near top left of screen as tho it's loading from tape.

Staticy fatty noise from speaker but can't tune it in to my crt perfectly. 

Booted pressing start and got the beep for loading. With no cart its just displaying the above mentioned blue screen. With basic cart it displays just black. Star raiders cart also same.  Replaced all 16k ram, reseated all chips and see fault remains. This is

where I reach my limit of fault finding and repair. The capacitor on main board replaced also. 

Can anyone with further knowledge shine any light? Would be nice to get this classic computer running again!

Many thanks

 

[Beeblebrox]

hi

 

you should boot to an atari memo screen on powering up. If you don't see this and just a blue screen/square cursor possibly the pokey chip is failing.

 

Also worth looking at the power board as well. I have an 800 with a faulty power board. Powers up but only to the blue screen and square cursor. If I swap out the power board with another all is ok.

 

also see here: 

 

Edited April 7, 2023 by Beeblebrox

[thax]

Thanks for your reply

That's a bummer if it's pokey, I don't have a spare and I won't risk a working one from any other of my ataris. 

Interestingly I can boot up holding start and get the beep, but can't get any other keys to start the load process. So could well be pokey. 

I haven't noticed any chips getting hot either. Maybe a bad connection on that multiple connector on power board? I need a schematic for what each pin is so will go look for service manual.

 

Thankyou again

[ClausB]

On 4/7/2023 at 11:22 AM, thax said:

The capacitor on main board replaced also. 

Which cap?