800XL black screen

[actualreality]

Hi all

 

I bought an 800xl from ebay last week. Plugged in and got 44 red squares and 4 green so ordered some sockets up and RAM chips (same as the C64 memory i believe)

 

Removed the old ram chips, added sockets and the new ram.

 

When i turned it on again i just got a black screen.

 

checked the psu voltage. Just over 5v. Also checked my solder joints and all good.

 

Would love to get this working so any advice would be greatly appreciated.

 

regards

darren

[_The Doctor__]

looks like you either shorted a trace or broke a trace.... make sure solder used is the old lead based solder and that it flowed all the way thru the pcb but not so much that it shorts the legs on on chips or sockets, make sure chip legs are in socket holes, are correct chip, and facing correct direction.

clear all flux make sure to use rosin not acid and get the best magnification and light you can find to really get a look at the work. Plug it all in and check again...

Edited March 6, 2014 by _The Doctor__

[Flash Gordon]

I remember I had a similar problem upgrading with a Rambo XL. The technician said I only soldered on one side of the board. He soldered on both sides and it worked.

[Bryan]

I remember I had a similar problem upgrading with a Rambo XL. The technician said I only soldered on one side of the board. He soldered on both sides and it worked.

That means you pulled out a plate-thru- the metal connecting the top and bottom pads like a bobbin. You can see the little tubes of metal stuck to the IC pins if you pull them out.

[feather]

Apart from that:

One of the new chip RAM defective. It is a version A800 with the chip Freddie? If so, replace it.

[Kyle22]

Apart from that:

One of the new chip RAM defective. It is a version A800 with the chip Freddie? If so, replace it.

Normal 800XLs do not have Freddie, only 800XLF does, along with the 1400, 1450 and the XE series.

[Arcanis-Will]

Did you double and triple check that you have the right parts and the right speed? Also that they are all oriented correctly?

[actualreality]

Did you double and triple check that you have the right parts and the right speed? Also that they are all oriented correctly?

 

 

All the correct way round (took photos at every stage to ensure that they were the same way around.

 

Chips pulled from the 800XL were MT4264-15 - replaced with KM4164B-15. From datasheets I cant see anything that would cause an issue.

 

I did check for broken traces etc before I added sockets, all fine. I guess I will have to remove them all again and solder the chips directly to the board, making sure I solder above and below the board. cant solder above of course at the moment as I have sockets on it.

 

Didn't think last night, but will also make sure each chip is getting a 5V supply and work from there I think.

[Marius]

Normal 800XLs do not have Freddie, only 800XLF does, along with the 1400, 1450 and the XE series.

 

Yeah, but the case still reads atari 800xl, so it is not so strange if someone does not notice the difference.

[Marius]

The chance you ruined the board is not so big. The fact that you had so many red blocks and now you have a non working atari with other memory.

Big chance something else is defect. Perhaps the LS158's or the MMU or indeed the new memory.

 

Do not solder memory on board…. sockets should be fine.

[actualreality]

The chance you ruined the board is not so big. The fact that you had so many red blocks and now you have a non working atari with other memory.

Big chance something else is defect. Perhaps the LS158's or the MMU or indeed the new memory.

 

Do not solder memory on board…. sockets should be fine.

Thanks - I do want to stick with sockets.

 

I bought full 2 sets of RAM as I change memory chips for people - my own Spectrum +2 and +3's for instance I removed the RAM and added sockets with no issue. Also done it to both of my C64's, again with no issue.

 

I have now checked the RAM pins have the correct voltage to them, and they do - measuring over the VCC (Pin 8 +5V) and VSS (Pin 16 Ground) each chip is getting 5.25V to them, so can only assume that something else has gone pop since I changed the RAM. As you say, maybe the MMU or LS158's!

 

I tried removing all socketed chips and re-seating them, but still nothing. Also tried turning the machine on with no ram chips in the sockets at all, but still nothing. Tried with the old RAM in which gave the error in the 1st place of 44 red squares - nothing again.

 

Always particularly careful when I'm completing work like this. Definitely didn't snag any traces or pulled through any "bobbins"..........

 

Edit: Just bought 2 x LS158's so will see how they fair.

 

All is not lost as I have my eye on another 800XL in any case, but would be really great to get this one working as I have spent so much time with it

Edited March 7, 2014 by actualreality

[Arcanis-Will]

You can test most of your soldering by probing the continuity across all 8 chips. Because the majority of the pins are common (I think all but Data In & Data Out), you should have continuity across all of them.

 

Look up the schematic for the board, or even simpler, look at the datasheet for the memory. Then identify all the common lines which is basically everything except the two data pins.

 

A quick example - pin 3 is /WE. If the memory is marked U9 - U16, then put 1 test lead on pin 3 of U9. You should have a solid connection to U10 pin 3, U11, pin 3, and so on.

 

This will verify socket / PCB trace connections and will tell you that all sockets are attached to the PCB. If you find that one doesn't then you need to touch up that pin. If none are reachable from the first socket then it might be the first socket with the issue.

 

Also, the schematic specifically calls for HM6864-2P, not 4164. I am not familiar with the difference between the 4164 and the 4864. Are they compatible?

 

ps - I would do this with power off to avoid accidental shorts to 5v or GND.

Edited March 7, 2014 by Arcanis-Will

[Arcanis-Will]

To expand on what ProWizard said - I found something else that can cause the black screen (if you can follow this hopefully it will make sense). Your symptom could be caused indirectly by a good GTIA which is affected by a failed chip select coming from either U2 (Address Decoder), or U3 (MMU).

 

It took me several hours of troubleshooting to determine that at the times that my dead 800XL works, all the signals from the GTIA are great, but when it fails, the GTIA is not getting accessed and the waveforms are not coming out. Probing the CS line on the GTIA yields garbage, not pulses. So that comes from U2 which is apparently fed garbage from U3. However other parts of U3 feed good pulses to the ROM chips. So in my case I think I have a damaged MMU.

 

If you have access to an oscilloscope you can identify the necessary signals using the SAMS Computer Facts Technical Service Manual.

 

This will let you determine if you see good pulses going to the RAM demux chips (U26, U27), to the ROM chips (U4, U5), and to the GTIA.

 

Also since you have a black screen you can look at the SAMS guide page 26/27/28 - the wide schematic - and see the sample waveforms at certain pins.

 

if you have a scope, check the signals. If not, try swapping GTIA, MMU, and Address Decoder (U7, U3, U2).