New to me Atari 800

[random_rodder]

For what it's worth, the PSU for my 800XL died a year ago. I've been using a lab power supply set at 5.25v to power it. When I get some time to search, I'll be looking for a small PC/AT power supply for it. I don't like wall warts...

[kikenovic]

I'm glad I found this tread. So, it is valid to use a modern supply as long as voltage is correct and current is at or above spec. I'm thinking of soldering this to an XEGS : https://goo.gl/r1zZef

[Kyle22]

That should work. just make sure to get the polarity right. Look at the picture in the link below. Note that the view is looking at the back of the computer. http://atariage.com/forums/topic/184792-800xl-power-supply-connector/?do=findComment&comment=2323544

[mozartpc27]

I got a new multimeter, and have tested both power supplies. It's an anlaogue meter, so I hope I am reading it right, but they both seem to be outputting about correctly, with the PSU that produces a kind of visual feedback with the computer hooked up to the television outputting at a slightly higher voltage than the one that just produces a black screen.

 

So, if it at least ONE of these power supplies works, what next?

[mozartpc27]

I am looking at the black "V.mA" numbers when attempting to read the meter. I can't confirm anywhere that "V.mA" = is just the voltage in the "5V" DC output I am looking for from the power supply. It's kind of frustrating me. What the hell is a V.mA unit?

Edited February 26, 2016 by mozartpc27

[Joey Z]

I am looking at the black "V.mA" numbers when attempting to read the meter. I can't confirm anywhere that "V.mA" = is just the voltage in the "5V" DC output I am looking for from the power supply. It's kind of frustrating me. What the hell is a V.mA unit?

Analog meters often share the same scale between multiple settings. V.mA is not one unit, but two which are read on the same scale. When measuring volts, or mA, you use that same scale. as long as you have the meter leads plugged into the V and common input, and you have it on a voltage measuring setting, you're measuring volts.

Edited February 26, 2016 by Joey Z

[mozartpc27]

Analog meters often share the same scale between multiple settings. V.mA is not one unit, but two which are read on the same scale. When measuring volts, or mA, you use that same scale. as long as you have the meter leads plugged into the V and common input, and you have it on a voltage measuring setting, you're measuring volts.

 

Aha. Well in that case, one of the two power supplies seems to be outputting slightly more than the promised 5V (the one that gives visual feedback on the screen), and the other is right at the number (could be a calibration issue - when I "zero out" the unit the needle moves ALL the way to the right - off the printed scale).

 

so it would seem at least one of these PSU is outputting the correct voltage. What ought I to try next? The RAM?

[Joey Z]

 

Aha. Well in that case, one of the two power supplies seems to be outputting slightly more than the promised 5V (the one that gives visual feedback on the screen), and the other is right at the number (could be a calibration issue - when I "zero out" the unit the needle moves ALL the way to the right - off the printed scale).

 

so it would seem at least one of these PSU is outputting the correct voltage. What ought I to try next? The RAM?

what do you mean 'zero out?'

[mozartpc27]

what do you mean 'zero out?'

 

I mean calibrating the multimeter. I watched an internet video about how to use an analog meter, here:

 

He explains how to make sure the meter reads zero resistance (i.e., needle is over 0) when there is in fact zero resistance.

[Joey Z]

 

I mean calibrating the multimeter. I watched an internet video about how to use an analog meter, here:

 

He explains how to make sure the meter reads zero resistance (i.e., needle is over 0) when there is in fact zero resistance.

zeroing only applies when you're measuring resistance, and the resistance zeroing function should have no effect on voltage readings. There is also usually a mechanical zero screw, but this should rarely, if ever, need adjustment.

[mozartpc27]

I see.

 

In either circumstance, the multimeter appears to tell me the power supplies are good... so my question is what should I try next in terms of trouble shooting, or is it even worth it?

[shoestring]

Don't just measure +5 from the power connector. Are you getting around +5v at any of the chips ( get a pinout of the chips & measure the voltage between gnd and vcc )

 

Does the red led even come on ?

 

Is the system playing blind ? ( ie.. Do you hear keystrokes from the 1084 speaker when you type on the keyboard ? Try the audio lead from the composite cable into the monitor. )

 

Have you tried re-seating any socketed chips ?

Edited February 27, 2016 by shoestring

[random_rodder]

I see.

 

In either circumstance, the multimeter appears to tell me the power supplies are good... so my question is what should I try next in terms of trouble shooting, or is it even worth it?

 

Maybe. The PSU can output 5vdc until it's connected to a load. If the output is weak, the 800xl might drag it down to nothing. I'm not as familiar with Atari's as I am TRS-80's, so YMMV with that comment.

 

Get a copy of Sam's Computerfacts for the 800xl. There will be several useful diagrams depicting test points and the expected voltages at those points (as well as waveforms at various TP's if you have a oscilloscope). In conjunction with testing Vcc at various chips, that will tell you if power is being routed as expected.

[mozartpc27]

Thanks... I need to get back to working on this, but haven't had a lot of spare time lately. The computer is sitting here and pulled apart.

[mozartpc27]

Don't just measure +5 from the power connector. Are you getting around +5v at any of the chips ( get a pinout of the chips & measure the voltage between gnd and vcc )

 

Does the red led even come on ?

 

Is the system playing blind ? ( ie.. Do you hear keystrokes from the 1084 speaker when you type on the keyboard ? Try the audio lead from the composite cable into the monitor. )

 

Have you tried re-seating any socketed chips ?

 

Every chip I've measured seems to be getting between 4-4.5 volts. When I just test the PSU, its outputting closer to 6.

 

The red light comes on.

 

I have yet to hear anything coming from the system. I've tried hooking it up to my tube TV via both RF and Composite, and to a Commodore monitor I have through composite. Nothing.

 

I just sat with the computer on for a few minutes - nothing seemed to be overheating.

 

I have re-socketed some, but not all, of the chips. 5 of the 8 RAM chips are sort of a bitch to get out - I don't want to damage them trying to re-socket them!

[shoestring]

4-4.5 volts from inside seems a bit too low.

 

ttl chips start to play up with voltages below 4.8v

[mozartpc27]

So is it the PSU? Or the board?

[shoestring]

If you've measured correctly then I would suspect a bad PSU.

 

I don't know which country you're in but this is the PSU used in Australia. I've used this for both my 800xl & 600xl. Mine is outputting 5.1v at the connector with no load ( computer switched off ).

 

 

Under load I'm measuring 5.05v which is acceptable. You'll get some drop in voltage which is normal. But if you're starting off by measuring 6v then measuring a big drop with the machine switched on then there's definitely a problem with the PSU and I wouldn't be using that power supply again. Get yourself a known working power supply.

Edited March 6, 2016 by shoestring

[BillC]

So is it the PSU? Or the board?

I would suspect the power supply, even without load it shouldn't output 6V. Is it an INGOT(picture below)?

This model of power supply is well known to fail with over-voltage output high enough to damage ICs.

 

[mozartpc27]

Yeah, it is an ingot.

 

OK, I can replace it. What other of my components will be fried? RAM, presumably, from what I've read.

[BillC]

Yeah, it is an ingot.

 

OK, I can replace it. What other of my components will be fried? RAM, presumably, from what I've read.

Back in the 80's I had an Ingot fail over-voltage(+8V) with a RamboXL upgraded 800XL, all that was damaged were the 256K RAM chips.

 

An electronics tech working for the phone company(a member of the local Atari users group) added a 7805 regulator inline to the output as a repair. I used it for awhile until I built one with crow-bar protection.

[shoestring]

Hard to speculate without replacing the PSU first & re-testing.

 

I doubt you've damaged the PCB if the load imposed is dragging the voltage down from 6v to way below 5v.

 

The danger is when the voltage at the chips is excessively high.

[mozartpc27]

I should have tested and posted this yesterday, but I have a second PSU that, when used to fire up the 800XL, produces only a *black* screen. There might be a flicker of orange for a second, but then black. The voltage out on this PSU is right around 5V, and that's what I get at all of the 8 RAM chips. However, at the longer chips across the "bottom" (if I am looking at the computer in its normal, ready-for-use position, but opened up), I get readings of 4V or less in some cases. I don't know what all the chips are so I haven't been able to find pinouts so I am testing correctly. I guess I should post a picture. I'll work on that. One is copyright 1979 Atari, another 1983.

[mozartpc27]

OK, so here we go:

 

 

I understand the bank of 8 smaller chips all the way on the left of the picture to be RAM - they all read at or near 5V (I am using an analog multimeter)with my other PSU, which reads at 5V at the DIN when it is not plugged into the computer. Additionally, all of the "smaller" chips - so the three that are nearest the bank of RAM on the left, the 7 grouped in the middle, and the two little guys to the right with the green wire running over them, will produce a reading of 5V with some orientation of the test leads (I am not always sure what is the ground and what the "positive" pin to use on these, but ultimately I was able to read 5V coming from all of them).

 

The question I have is now about the four across the bottom, and the three running lengthwise above them on the right. I have included all the information from the labels of the chips in this list. They are listed across from left to right (the first 4), then in ascending order up from above the last in the line of horizontally oriented chips at the bottom (the last three):

 

Bottom Across, left to right:

 

OKI Japan © 1979 Atari, M3983 C014805-22: Ground test lead positioned bottom right, positive test lead positioned top left: 4V

 

IMP 8324 LGA C021697-31 © 1983 Atari: Ground test lead positioned bottom left, positive test lead positioned top right: 5V (if I do this one with the ground test lead positioned bottom right and positive test lead positioned top left, it reads around 1.5V)

 

8311 C-014806-03? (last digit(s) too faded to read): Ground test lead positioned bottom right, positive test lead positioned top left: 4V

 

C014795-12 R6520-26 8324: Ground test lead positioned bottom left, positive test lead positioned top right: 4V

 

Moving upward one at a time from the last chip in that bottom row (C014795-12):

 

AMI 8328BLE C0122948-01 C03051 Korea: Ground test lead positioned bottom left, positive test lead positioned top right: 5V

 

Label fell off, lost it (it was inside the computer when I opened it up, saw it, don't know where it got to): Ground test lead positioned bottom right, positive test lead positioned top left: 5V

 

NCR2364-30 F807612 N8326 C060302A-29 © 1979 Atari: Ground test lead positioned bottom right, positive test lead positioned top left: 5V

Edited March 6, 2016 by mozartpc27

[Joey Z]

OK, so here we go:

 

 

I understand the bank of 8 smaller chips all the way on the left of the picture to be RAM - they all read at or near 5V (I am using an analog multimeter)with my other PSU, which reads at 5V at the DIN when it is not plugged into the computer. Additionally, all of the "smaller" chips - so the three that are nearest the bank of RAM on the left, the 7 grouped in the middle, and the two little guys to the right with the green wire running over them, will produce a reading of 5V with some orientation of the test leads (I am not always sure what is the ground and what the "positive" pin to use on these, but ultimately I was able to read 5V coming from all of them).

 

The question I have is now about the four across the bottom, and the three running lengthwise above them on the right. I have included all the information from the labels of the chips in this list. They are listed across from left to right (the first 4), then in ascending order up from above the last in the line of horizontally oriented chips at the bottom (the last three):

 

Bottom Across, left to right:

 

OKI Japan © 1979 Atari, M3983 C014805-22: Ground test lead positioned bottom right, positive test lead positioned top left: 4V

 

IMP 8324 LGA C021697-31 © 1983 Atari: Ground test lead positioned bottom left, positive test lead positioned top right: 5V (if I do this one with the ground test lead positioned bottom right and positive test lead positioned top left, it reads around 1.5V)

 

8311 C-014806-03? (last digit(s) too faded to read): Ground test lead positioned bottom right, positive test lead positioned top left: 4V

 

C014795-12 R6520-26 8324: Ground test lead positioned bottom left, positive test lead positioned top right: 4V

 

Moving upward one at a time from the last chip in that bottom row (C014795-12):

 

AMI 8328BLE C0122948-01 C03051 Korea: Ground test lead positioned bottom left, positive test lead positioned top right: 5V

 

Label fell off, lost it (it was inside the computer when I opened it up, saw it, don't know where it got to): Ground test lead positioned bottom right, positive test lead positioned top left: 5V

 

NCR2364-30 F807612 N8326 C060302A-29 © 1979 Atari: Ground test lead positioned bottom right, positive test lead positioned top left: 5V

the big chips don't have power pins in the 'normal' places. see pinouts here: http://www.atarimax.com/jindroush.atari.org/achip.html

 

If you follow the links at the top of the page, you can get a list of the atari part numbers along with pinout pictures.

Edited March 6, 2016 by Joey Z