Black screen

[wiliv]

I've just tried out an 800XL that was boxed for many years and I didn't know if it worked before.

 

It didn't have any cables or power supply with it. So I used a PC ATX to supply the 5 volts and wired +5V to pins 1,4 and GND to pins 3,5,2 of a DIN plug (as described in various places). However I didn't have a 7 pin DIN connector so I used a 5 pin. I don't know if that is good enough?

 

Anyway, I've triple checked that it provided the power on the right pins as I intended it before plugging it in the Atari. I also connected a TV via RF cable. When turning it on, the power led goes on, I tuned the TV and get a signal. But only a black screen. Sometimes when turning it off/on there's an orange color for a fraction of a second before it turns to black.

 

Any ideas where to go from here ?

 

Thanks,

 

Wim

[Rybags]

IIRC only 2 pins are connected on the incoming power jack anyway, so that's fine.

 

Generally you'll get a brief flash of orange/brown when you turn the Atari on, before the OS clears the colour registers. Your description would indicate that at least the CPU is OK.

 

The OS seems to be at least partially OK.

 

The best thing to do early on for something like this is to gently lever up all of the larger custom ICs and the RAM ICs. Lift each side such that the pins come up by about 1 mm or so, then push straight back in.

 

ed - I'd probably concentrate on the RAM and OS ICs first - RAM are the 8 alike ones down the left hand side, OS should be the larger of the 2 chips up near the top right.

 

That'll help to remove any oxidation on the pins that could cause problems.

Edited June 4, 2010 by Rybags

[atariksi]

I've just tried out an 800XL that was boxed for many years and I didn't know if it worked before.

 

It didn't have any cables or power supply with it. So I used a PC ATX to supply the 5 volts and wired +5V to pins 1,4 and GND to pins 3,5,2 of a DIN plug (as described in various places). However I didn't have a 7 pin DIN connector so I used a 5 pin. I don't know if that is good enough?

 

Anyway, I've triple checked that it provided the power on the right pins as I intended it before plugging it in the Atari. I also connected a TV via RF cable. When turning it on, the power led goes on, I tuned the TV and get a signal. But only a black screen. Sometimes when turning it off/on there's an orange color for a fraction of a second before it turns to black.

 

Any ideas where to go from here ?

 

Thanks,

 

Wim

 

Yeah, as Rybags stated-- oxidation on RAM/ROM chips. You can also get a reddish/orange screen sometimes if the cart is not inserted properly or has bad contacts. I have seen a red screen on a perfectly working machine because the cart contacts were bad or the cart's contacts themselves had oxidation.

[wiliv]

Thanks for the detailed help so far.

 

The unit is indeed rather dirty/dusty but inside the RF shield it looks clean. There's even some rust traces on the big conduct strip where the RF shield sits.

 

So I've lifted and pushed back the 2 ROMs, 8 RAMs and the 5 big ICs. Even tried some of the smaller ones.

 

The contacts on the card slot seem ok but I cleaned them anyway. Also the expansion bus was very dirty so cleaned that as well.

 

But it's still giving the same black screen.

 

Any more ideas to try ? I don't have any other atari's so I can't swap component for instance.

 

Would dirt in the keyboard part be able to cause that? (at first there was a key stuck) Can I test with the keyboard cable removed?

 

PS: I should also say that during one of the tests I accidently connected the power supply to the monitor port for a few seconds. Whould that be really bad? At least it still gives the same orange then black screen. (now I know why the power has a 7 pin DIN connector )

[Rybags]

Power to the monitor port... not exactly a great idea, but chances are if it fried anything you'd not even get a black screen now.

Running without a keyboard is fine, won't affect the machine's ability to start up.

 

Don't suppose you have any game cartridges? Star Raiders would be helpful - it gets control of the system early on and only uses 8K RAM so will often show signs of life in a system that otherwise mightn't start up properly.

 

If you have an oscilloscope, then you could probably use it to help check for signs of life in specific places.

 

Other than what's already been done... can't think of much. The MMU is another important chip you might want to lift/reseat. It should be the medium sized IC directly below the cartridge slot, right hand side.

 

Another check to make might be to ensure there's nothing metallic in the joystick or serial ports that could be shorting pins.

 

Another check, just incase the machine is working but the picture is not right for some reason - turn up the TV volume and press some keys, see if you're getting a keyclick.

 

 

Finally - what about the capacitors - are any bulging or leaking fluid?

Edited June 5, 2010 by Rybags

[wiliv]

No cartridges. Only a disk drive (but no cable) and a "koala pad"

 

Reseated the MMU (at least a small ic marked C061618) and by now pratically all of the small ICs.

 

No shortages found and I see nothing suspicious about the capacitors.

 

I don't have an oscilloscope.

 

Tried with keyboard disconnected: same result.

 

Tried pressing keys, no sound on TV, nor on the stereo connected to monitor pin 3.

 

Also connected a PAL monitor on pin 1 or 4 of the monitor port, again sync but black.

 

Damn, I don't like giving up...

[Rybags]

What's your location? There might be someone nearby that could help - I reckon the best next thing is to do the swapover test on the major chips.

[wiliv]

What's your location? There might be someone nearby that could help - I reckon the best next thing is to do the swapover test on the major chips.

 

I live in Antwerp (Belgium)

 

Yeah, I guess I'll need to find some spare parts first. Even if I get it working I'm still missing a SIO cable to connect the disk drive and make it do something, but I've never seen such connectors before...

 

Again thanks for the excellent help.

 

Wim.

[pseudo_intellectual]

I have an 800XL with essentially the same problem. Whether using the RF or composite connections, I see a brief flash on the screen followed by solid black video. No noise is present when I press the keys. This occurs regardless of whether I am using a cartridge (I've tried several) or without. The first thing I do, seeing that all the ICs are socketed, is remove them with a chip puller and reseat them. I didn't observe any rust or oxidation on any of the ICs I reseated.

 

Armed with a meter, logic probe, and some schematics I started digging. With these in hand I made the following observations:

 

* The power is good. I see +5V on all the ICs which require it.

* The CPU appears to be functioning. I see pulsing of the address and data lines. The reset circuit also appears to be functioning. I see the /RESET signal pulse on it remains HIGH shortly after releasing the reset button.

* The peripheral chip selects for the PIA, POKEY, and GTIA are being pulsed, which appears to indicate that the CPU, for its part, is attempting to access the address space of these ICs. This seems to preclude that the address decoding circuitry and the MMU is at fault. The /HALT signal is being pulsed continuously. This signal is responsible for determining address bus access between the ANTIC and the CPU, right?

* The chip select for the OS ROM pulses continuously for 2-3 seconds before remaining high until the next reset.

* I never see the chip select for the BASIC ROM be driven low with repeated resets.

* I see that the PIA is using some of the PORTB pins to drive the MMU. However, I never see PB0, PB1, or PB7 pulse whatsoever. I do see that PB2 and PB3 pulse momentarily on startup so I am assuming (perhaps mistakenly) that the CPU is somehow able to initialize PORTB on the PIA. Perhaps the PIA is okay? Would the machine give me anything other than a black screen if the PIA was malfunctioning?

* I am not at all certain about the GTIA and the ANTIC. I can only assume that the GTIA is providing a valid signal. The voltage levels coming off of the video amplifier appear to be okay and my television's OSD clears when the machine is on and reappears when it's off. To know any more would require a scope, it seems.

* I have no way to determine if the RAM is good. Changing the RAM positions didn't affect the outcome.

* I really wanted to get to the self test, but I've been unable to activate it (pressing OPTION along with reset, right?).

 

 

Unfortunately, I haven't a spare machine to swap ICs. Save for the RAM and (maybe?) the 6520, it appears that everything else will require finding another machine to swap parts. Does anyone have any recommendations about isolating the particular part (or parts). I'd like to troubleshoot this thing as intelligently as I can, and I had hoped that perhaps someone has run into similar issues or would otherwise know what this machine should be (or not be) doing within the first few seconds of flipping the switch.

 

Thanks in advance!

[Rybags]

Antic generates continual bus activity which might give false signs of a healthy 6502.

 

Possibly the Sync line on the 6502 would be a good test point (it's present on Sally too?)

 

But, even then, unsure what would occur with that in the case the machine crashed on an illegal opcode which causes the 6502 to internally loop.

[+bob1200xl]

I have both a scope and a logic analyzer, but it always seems to end up swapping parts. Maybe check for hot RAM chips and try replacing them.

 

The OS goes through a lot of resets and RAM/ROM testing before it starts the GR.0 screen. Usually, a RAM/memory failure will throw the system out in to the weeds and you end up with a black screen. If the system fails early, you get a colored screen since the CPU hasn't even run resets.

 

You have ROM select activity and a black screen, so I would expect that the CPU and ROM circuits are OK. Does it even select RAM? Something has to be selected on every instruction at some point in time. If you have no RAM select, the MMU may be bad.

 

Really, if you are going to work an an Atari (or anything else) you need a known, good spare.

 

Bob

 

 

 

I have an 800XL with essentially the same problem. Whether using the RF or composite connections, I see a brief flash on the screen followed by solid black video. No noise is present when I press the keys. This occurs regardless of whether I am using a cartridge (I've tried several) or without. The first thing I do, seeing that all the ICs are socketed, is remove them with a chip puller and reseat them. I didn't observe any rust or oxidation on any of the ICs I reseated.

 

Armed with a meter, logic probe, and some schematics I started digging. With these in hand I made the following observations:

 

* The power is good. I see +5V on all the ICs which require it.

* The CPU appears to be functioning. I see pulsing of the address and data lines. The reset circuit also appears to be functioning. I see the /RESET signal pulse on it remains HIGH shortly after releasing the reset button.

* The peripheral chip selects for the PIA, POKEY, and GTIA are being pulsed, which appears to indicate that the CPU, for its part, is attempting to access the address space of these ICs. This seems to preclude that the address decoding circuitry and the MMU is at fault. The /HALT signal is being pulsed continuously. This signal is responsible for determining address bus access between the ANTIC and the CPU, right?

* The chip select for the OS ROM pulses continuously for 2-3 seconds before remaining high until the next reset.

* I never see the chip select for the BASIC ROM be driven low with repeated resets.

* I see that the PIA is using some of the PORTB pins to drive the MMU. However, I never see PB0, PB1, or PB7 pulse whatsoever. I do see that PB2 and PB3 pulse momentarily on startup so I am assuming (perhaps mistakenly) that the CPU is somehow able to initialize PORTB on the PIA. Perhaps the PIA is okay? Would the machine give me anything other than a black screen if the PIA was malfunctioning?

* I am not at all certain about the GTIA and the ANTIC. I can only assume that the GTIA is providing a valid signal. The voltage levels coming off of the video amplifier appear to be okay and my television's OSD clears when the machine is on and reappears when it's off. To know any more would require a scope, it seems.

* I have no way to determine if the RAM is good. Changing the RAM positions didn't affect the outcome.

* I really wanted to get to the self test, but I've been unable to activate it (pressing OPTION along with reset, right?).

 

 

Unfortunately, I haven't a spare machine to swap ICs. Save for the RAM and (maybe?) the 6520, it appears that everything else will require finding another machine to swap parts. Does anyone have any recommendations about isolating the particular part (or parts). I'd like to troubleshoot this thing as intelligently as I can, and I had hoped that perhaps someone has run into similar issues or would otherwise know what this machine should be (or not be) doing within the first few seconds of flipping the switch.

 

Thanks in advance!

[pseudo_intellectual]

I have both a scope and a logic analyzer, but it always seems to end up swapping parts. Maybe check for hot RAM chips and try replacing them.

 

The OS goes through a lot of resets and RAM/ROM testing before it starts the GR.0 screen. Usually, a RAM/memory failure will throw the system out in to the weeds and you end up with a black screen. If the system fails early, you get a colored screen since the CPU hasn't even run resets.

 

You have ROM select activity and a black screen, so I would expect that the CPU and ROM circuits are OK. Does it even select RAM? Something has to be selected on every instruction at some point in time. If you have no RAM select, the MMU may be bad.

 

Really, if you are going to work an an Atari (or anything else) you need a known, good spare.

 

Bob

 

Bob:

 

Thanks for your response. I had a few days to sleep on the problem and in light of your suggestions I decided to lug it out for some more troubleshooting.

 

I initially looked at the RAM, but not nearly as much as I should have (and my observations probably reflect that). I'm not familiar with DRAM refresh circuity, so a lot of what was going on in the schematic was confusing me. I suppose it is as good of a time as any to learn.

 

I see that the /RAS and /CAS signals are pulsing, as are the data in and data out ports on all 8 of the DRAM ICs. Suddenly I realized that the /WE was stuck high the entire time (can't believe I missed that). I see the CPU is properly pulsing this signal, but it is not passing through the output of U28. It turns out that the latch signal on U28 is driven by pin 6 of the delay line, which is stuck on high the entire time. Based on this, I'm wondering if this is the culprit; I can't see the CPU having a lot of success writing to RAM if the write enable on the DRAM is stuck.

 

What do you think of this? I don't have any detailed documents on the delay line so I may be grasping at straws.

 

Even if I am correct in that I need a delay line, I suspect I'm going to have a lot of trouble finding one unless it comes out of another dead system, so I may have to concede that I'll have to wait for a spare unless someone has some spare delay line ICs floating around...

 

PS: Forgot to mention that the "delay line" I'm referring to is U29.

Edited June 22, 2010 by pseudo_intellectual

[Rybags]

http://www.best-electronics-ca.com/custom-i.htm

 

They have them on the Best page for 5 bucks, no idea if they have stock though.

 

Sounds plausible - if the Write line isn't working, then the OS will have no way of detecting how much RAM the system has, and won't be able to establish a display, let alone drop into Self-Test.

[pseudo_intellectual]

Just thought I'd follow up with what happened after the last post, if for no other reason than to help others in a similar situation.

 

It turns out that the delay line (U29) was, in fact, the culprit. I got a replacement from Best Electronics and after putting it in the machine fired up immediately. Better yet, there doesn't appear to be any other damage. The self test finds all the RAM successfully and I didn't encounter any other problems while playing the few game cartridges I have. Is the delay line a frequently failing component?

 

I got this thing off of eBay for $7 +shipping which may have been too much considering the work and parts I had to put into it. In hindsight, something should have tipped me off when he was parting the disk drive and the software separately and his description said something to the effect of "the power light comes on but I didn't have a video cable to test further." On the other hand, I probably got more entertainment value troubleshooting it than if it worked immediately.

 

Now all I have to do is go find something to do with it. I've never written 6502 assembly before; maybe it's time to learn

 

Thanks all to who gave suggestions.

[sloopy]

sounds like you might be familiar enough with the internals to do some mods... :') maybe 256k? heh...

 

sloopy.