Atari 800xl Black screen. All chips except ROMs tested

[Mudmin]

Thanks in advance for reading. I've followed a bunch of guides on the site for my XL with black screen (USB powered).  All ram, 74xx 40xx and custom chips test okay in my Backbit Chip tester.  The only 2 chips I can't test are the 2 roms.  I have another 800xl that works, but of course, those are the only 2 non-socketed chips on there.

Is there a way to test those 2 roms before I start going farther?  I was reading that I can replace the OS rom with a 27c128. Is that true?  Then just use the Rev2 ROM?

 

What about the other roms.  

Nothing gets hot.  Holding option then select start doesn't do anything.  SALT cartridge doesn't do anything.  Is there anything else I'm missing?

[TGB1718]

Have you checked you are getting +5VDC at the chips themselves ?

Some USB PSU's can't supply enough current to power the 800XL, to be

safe, preferably one that can provide 2 Amps

[_The Doctor__]

USB power has to be thoroughly checked, they have been known to be noisy, or not able to supply enough voltage/current (brownout conditions are hard on these chips), they have been shown to pulse power from high to low, some are 'intelligent' and won't adjust output without feedback transistors or handshake communication. Better off with standard power supplies or meanwell power supplies. When USB supplies blow it's a crap shoot as well depending on who made it.

[Beeblebrox]

@Mudmin few more bits of info needed. Is your 800xl socketed?

 

Can you upload a pic of the motherboard. 

 

Was it working until recently? 

 

When you power up does the monitor recognise a signal, but it's just black? 

Turn sound up, do you hear pops when powering up. 

 

If a socketed machine then it could be some bad sockets rather than chips themselves. 

 

Bad cpu can be a cause also. 

 

 

[Mudmin]

3 hours ago, TGB1718 said:

Have you checked you are getting +5VDC at the chips themselves ?

Some USB PSU's can't supply enough current to power the 800XL, to be

safe, preferably one that can provide 2 Amps

I'm getting 4.9 at pin 8 of the ram. I'm using a quality GaN charger.  It also powers the other 800xl without issue.

[Mudmin]

2 hours ago, _The Doctor__ said:

USB power has to be thoroughly checked, they have been known to be noisy, or not able to supply enough voltage/current (brownout conditions are hard on these chips), they have been shown to pulse power from high to low, some are 'intelligent' and won't adjust output without feedback transistors or handshake communication. Better off with standard power supplies or meanwell power supplies. When USB supplies blow it's a crap shoot as well depending on who made it.

I can power it from my bench PSU, but it does work without issue on the other 800xl

[Mudmin]

1 hour ago, Beeblebrox said:

@Mudmin few more bits of info needed. Is your 800xl socketed?

 

Can you upload a pic of the motherboard. 

 

Was it working until recently? 

 

When you power up does the monitor recognise a signal, but it's just black? 

Turn sound up, do you hear pops when powering up. 

 

If a socketed machine then it could be some bad sockets rather than chips themselves. 

 

Bad cpu can be a cause also. 

 

 

Here are some photos

I just got it. I've never seen this one work.  It does seem like it recognizes.  The screen goes from snow to black. I hear the occasional pop and a little squealing when connected over rf

[Beeblebrox]

14 minutes ago, Mudmin said:

Here are some photos

I just got it. I've never seen this one work.  It does seem like it recognizes.  The screen goes from snow to black. I hear the occasional pop and a little squealing when connected over rf

OK, so good news it's a fully socketed machine. Makes it easier. Also it's an ntsc machine. So you are on rf, OK, good to know. When you tune the TV do you get one channel come up, but just a black screen?

Have you lifted and pushed down on all chips in the board to reseat them? 40 years sitting in sockets can see oxidisation of sockets /chip legs, meaning bad contact. 

 

FYI chips can die easily. So it could be one or more chips (cpu for example) have just died.

 

Do the re seating of all chips and see if you get any change. 

[TZJB]

8 hours ago, Mudmin said:

Thanks in advance for reading. I've followed a bunch of guides on the site for my XL with black screen (USB powered).  All ram, 74xx 40xx and custom chips test okay in my Backbit Chip tester.  The only 2 chips I can't test are the 2 roms.  I have another 800xl that works, but of course, those are the only 2 non-socketed chips on there.

Is there a way to test those 2 roms before I start going farther?  I was reading that I can replace the OS rom with a 27c128. Is that true?  Then just use the Rev2 ROM?

 

What about the other roms.  

Nothing gets hot.  Holding option then select start doesn't do anything.  SALT cartridge doesn't do anything.  Is there anything else I'm missing?

 

800XL NTSC it is. It looks in good condition. I particularly like the very neat foam pad across the PBI traces. Most of have a bit of wonky masking tape!

 

It's also a bit unusual to actually use the modulator for the display these days. There is a chance it's faulty. Is it possible for you to connect the 800XL monitor port to the TV composite input?

 

Regarding the OS ROM. It can be replaced with a 28 pin EPROM from 27128 up to 27512 quite easily. By default, the ROM code needs to be in the upper end of the ROM because the Atari holds the extra address pins high.

 

For instance a 27128 will take a full 16KB image from 0000 to 3FFF. A 27256 would need the image moved to range 4000-7FFF and a 27512 the image moved to the range C000 to FFFF.

 

You may gather that a 27512 can hold 4 operating systems in total. These may be physically switched by isolating pins 1 and 27 from the Atari which as I said, holds them high, and pulling them high with 4K7 resistors connected to VCC. Switching them to ground in a binary fashion, each of the four OS can be selected individually. This is a very easy and common optional upgrade.

 

 

 

[Mudmin]

12 hours ago, Beeblebrox said:

OK, so good news it's a fully socketed machine. Makes it easier. Also it's an ntsc machine. So you are on rf, OK, good to know. When you tune the TV do you get one channel come up, but just a black screen?

Have you lifted and pushed down on all chips in the board to reseat them? 40 years sitting in sockets can see oxidisation of sockets /chip legs, meaning bad contact. 

 

FYI chips can die easily. So it could be one or more chips (cpu for example) have just died.

 

Do the re seating of all chips and see if you get any change. 

I pulled every custom chip (except the ROMS) tested and tested them on the latest firmware of the Backbit chip tester.  I also tested the ram chips, the 74 and 40 series logic. Deoxited the sockets and re-put them back in.  

The TV goes from snow to black screen when the unit turns on, so something is happening.  But that's all I can tell there.

 

[Mudmin]

9 hours ago, TZJB said:

 

800XL NTSC it is. It looks in good condition. I particularly like the very neat foam pad across the PBI traces. Most of have a bit of wonky masking tape!

 

It's also a bit unusual to actually use the modulator for the display these days. There is a chance it's faulty. Is it possible for you to connect the 800XL monitor port to the TV composite input?

 

Regarding the OS ROM. It can be replaced with a 28 pin EPROM from 27128 up to 27512 quite easily. By default, the ROM code needs to be in the upper end of the ROM because the Atari holds the extra address pins high.

 

For instance a 27128 will take a full 16KB image from 0000 to 3FFF. A 27256 would need the image moved to range 4000-7FFF and a 27512 the image moved to the range C000 to FFFF.

 

You may gather that a 27512 can hold 4 operating systems in total. These may be physically switched by isolating pins 1 and 27 from the Atari which as I said, holds them high, and pulling them high with 4K7 resistors connected to VCC. Switching them to ground in a binary fashion, each of the four OS can be selected individually. This is a very easy and common optional upgrade.

 

 

 

Thanks so much for this. I have tried both the monitor port on composite and the rf with the same results.  Are there particular 16k OS that I should look to burn on this thing?  I have plenty of EPROMS and a burner, so I'd like to at least eliminate that.  

What are the symptoms if the other rom goes bad?  I do have some adapters for those xx32 roms, so I could theoretically replace that too if I knew what to put on it.  

I'll be digging out the scope after this, I just figure you all are the experts and I might as well tackle the "common" faults first.

What about the other rom?  

[+kheller2]

You can pull the basic ROM and see if it boots and replace the OS ROM with an EPROM as suggested. I know you said all the chips test correctly, but have you actually swapped them into your working unit?

[TZJB]

1 hour ago, Mudmin said:

Thanks so much for this. I have tried both the monitor port on composite and the rf with the same results.  Are there particular 16k OS that I should look to burn on this thing?  I have plenty of EPROMS and a burner, so I'd like to at least eliminate that.  

What are the symptoms if the other rom goes bad?  I do have some adapters for those xx32 roms, so I could theoretically replace that too if I knew what to put on it.  

I'll be digging out the scope after this, I just figure you all are the experts and I might as well tackle the "common" faults first.

What about the other rom?  

 

The smaller 24 pin ROM is 8KB Atari BASIC and can be removed as @kheller2 advised.

 

For an Atari XL a Rev. 2 or 3 ROM is often the default. Please find the Rev. 3 image attached.

 

Atari OS Rev. 3 {29F133F7}.rom

[TZJB]

Just to add that a black screen normally means the processor is not booting.

 

Due to the nature of the Data and Address buses connecting many components, a black screen can be due to many things including a continuity problem.

 

If just one trace is faulty you could see the black screen. I have had this happen when installing sockets and a trace breaks (Atari XE normally) this one break between a RAM address causes complete failure. Other people have had a disconnection at a socket, which can often occur at the sockets themselves when they are standard Atari single wipe sockets.

 

As a suggestion, when you run out of chips to check then simple continuity checks with an Ohmmeter may prove fruitful.

 

Start at the RAM chips where most pins should be connected to one another except for pins 2 and 14 which should be connected at each chip and then to the Data bus via R140 to R147.

 

The memory address lines MA0-MA7 should each then be continuous to the decoder circuit of U26 & U27 via 33R resistors. Likewise RAS & CAS can be traced back to U30 via 33R resistors.

 

Please find diagrams attached.

 

 

Atari800XL_schematics_rev2.pdf

 

[_The Doctor__]

make sure all chip legs are making contact with socket swipes the legs should be slightly in the direction of the swipes all the way around. Make sure there are no fleks of matter between any pads or traces inbetween sockets or on the mother board anywhere. Check for cracks or corrosion of all solder joints, swap out ROM and Basic chips with a known good Atari. Make sure all chip legs are in each and every socket hole.

After that it's time to check the support chips and transistors, and for any blown, fat or leaked dried out caps. No cracked or broken components around the chips where folks pry sometimes?

Edited April 7 by _The Doctor__

[Mudmin]

Just in general I want to thank everyone for the kind and helpful responses. Everyone has been wonderful.

 

[Mudmin]

10 hours ago, kheller2 said:

You can pull the basic ROM and see if it boots and replace the OS ROM with an EPROM as suggested. I know you said all the chips test correctly, but have you actually swapped them into your working unit?

I replaced the ram entirely, and did one chip swap, but the chips are stuck enough in my working one that it's not worth damaging it to try to get this one working.  I definitely know that the chip tester can only pretty much guarantee me that something does not work and it can't guarantee me that it does.  I'm going to try to narrow something down to a potential problem before I start prying any more on my good one.

[Mudmin]

7 hours ago, TZJB said:

Just to add that a black screen normally means the processor is not booting.

 

Due to the nature of the Data and Address buses connecting many components, a black screen can be due to many things including a continuity problem.

 

If just one trace is faulty you could see the black screen. I have had this happen when installing sockets and a trace breaks (Atari XE normally) this one break between a RAM address causes complete failure. Other people have had a disconnection at a socket, which can often occur at the sockets themselves when they are standard Atari single wipe sockets.

 

As a suggestion, when you run out of chips to check then simple continuity checks with an Ohmmeter may prove fruitful.

 

Start at the RAM chips where most pins should be connected to one another except for pins 2 and 14 which should be connected at each chip and then to the Data bus via R140 to R147.

 

The memory address lines MA0-MA7 should each then be continuous to the decoder circuit of U26 & U27 via 33R resistors. Likewise RAS & CAS can be traced back to U30 via 33R resistors.

 

Please find diagrams attached.

Thanks so much for these. I did do the ram continuity check. I need to trace the rest of them out.  I'm going to get my scope out too and try to follow the path to see what's happening. This stuff will be super helpful. 

7 hours ago, TZJB said:

 

 

Atari800XL_schematics_rev2.pdf 589.69 kB · 1 download

 

 

[Mudmin]

8 hours ago, TZJB said:

 

The smaller 24 pin ROM is 8KB Atari BASIC and can be removed as @kheller2 advised.

 

For an Atari XL a Rev. 2 or 3 ROM is often the default. Please find the Rev. 3 image attached.

 

Atari OS Rev. 3 {29F133F7}.rom 16 kB · 0 downloads

Thanks so much for this. I pulled the basic ROM. No change.  I burned the OS rom and nothing in particular. Although when it's been off for a while and I first turn it on, I see a few things that look like "intentional" colors on the screen. So something is going on there now that I don't think was before.

[+kheller2]

If you have a working 800XL, then its time to start putting the bad unit's chips into the working 800XL.

[TZJB]

40 minutes ago, kheller2 said:

If you have a working 800XL, then its time to start putting the bad unit's chips into the working 800XL.

 

That is normally the best course of action, however the working 800XL is fully soldered in as I understand it.

 

It would take lots of work with a de-soldering station to actually achieve any swaps so I can understand when @Mudmin shows reluctance to that prospect.

 

If it were me, I would get out the trusty fully socketed 600XL! But not everyone has one to hand.

 

 

[Beeblebrox]

7 hours ago, TZJB said:

 

That is normally the best course of action, however the working 800XL is fully soldered in as I understand it.

 

It would take lots of work with a de-soldering station to actually achieve any swaps so I can understand when @Mudmin shows reluctance to that prospect.

 

If it were me, I would get out the trusty fully socketed 600XL! But not everyone has one to hand.

 

 

It's a socketed 800xl thankfully as illustrated in the pics the op linked to earlier. 

[TZJB]

6 hours ago, Beeblebrox said:

It's a socketed 800xl thankfully as illustrated in the pics the op linked to earlier. 

 

I agree, the faulty illustrated 800XL is socketed however, and I may have mis-understood, but I thought the second working 800XL was of the soldered in variety otherwise @Mudmin would have swapped chips?

 

But then it's not our call. Over to @Mudmin for clarification.

[+kheller2]

The working board just has the ROMs soldered, or so that is how I read the first post.   

[Mudmin]

The working one does just have the roms soldered.  Next time I can get some bench time I'll  definitely do the chip swap and see if I get lucky.  I appreciate everyone's help!