Atari 800 SIO issue

[JGRAHAM2]

I have an 800 that works great, except for SIO. It will not boot from an S-Drive Max or FujiNet even if they are externally powered. I have tried to replace all daughter cards with spares and also all major ICs on the motherboard. Anyone have any ideas on how to troubleshoot?

[TGB1718]

Check inside the SIO socket in case anything is across the pins, Check the SIO socket solder joints on the motherboard, re-flow with solder.

 

[JGRAHAM2]

32 minutes ago, TGB1718 said:

Check inside the SIO socket in case anything is across the pins, Check the SIO socket solder joints on the motherboard, re-flow with solder.

 

I did that and no difference. I, at first, thought Pokey or PIA, but tried both and that’s not it.

[ACML]

2 hours ago, JGRAHAM2 said:

I have an 800 that works great, except for SIO. It will not boot from an S-Drive Max or FujiNet even if they are externally powered. I have tried to replace all daughter cards with spares and also all major ICs on the motherboard. Anyone have any ideas on how to troubleshoot?

Just had the same thing happen on my 1200XL two days ago.  Replaced POKEY and PIA and that did not fix.  As a last resort, I blew compress air over the board and under the sockets and "BAM!" it works great.  This is the second time I've had this issue on two different machines and both times, compressed air magically made them right.  I have no idea why, but it worked twice.  Same issue, everything worked, but no boot on SIO.  Go figure.  I used canned air for electronics.  Shop air might have too much static electricity.

  

[JGRAHAM2]

43 minutes ago, ACML said:

Just had the same thing happen on my 1200XL two days ago.  Replaced POKEY and PIA and that did not fix.  As a last resort, I blew compress air over the board and under the sockets and "BAM!" it works great.  This is the second time I've had this issue on two different machines and both times, compressed air magically made them right.  I have no idea why, but it worked twice.  Same issue, everything worked, but no boot on SIO.  Go figure.  I used canned air for electronics.  Shop air might have too much static electricity.

  

I wonder if you had something conductive shorting something out and the air dislodged it. I had an issue recently with a 130XE and it was a bit of solder. 

[sup8pdct]

Check out R168 - R174. Make sure they are 100ohm.

Check out strip resistor R129, 4.7 kohm pullup. make sure one hasn't done something stupid.

Assume keyboard works so can rule out IRQ not working.

also check continuity between mother board and SIO connector, make sure the powerboard connector is ok.

[_The Doctor__]

yeah folks don't always clean up  after their handy work... solder flakes, solder pebbles, wire bits and whisker snips abound and create havoc... so remember to mop up your flux, brush up the board and blow out the bits of crap.

[JGRAHAM2]

13 hours ago, sup8pdct said:

Check out R168 - R174. Make sure they are 100ohm.

Check out strip resistor R129, 4.7 kohm pullup. make sure one hasn't done something stupid.

Assume keyboard works so can rule out IRQ not working.

also check continuity between mother board and SIO connector, make sure the powerboard connector is ok.

Thanks, I will do this later today and report back here.

[JGRAHAM2]

9 hours ago, JGRAHAM2 said:

Thanks, I will do this later today and report back here.

I checked the resistors and all look good. Continuity looks good. Voltages look good at the power board/mainboard connector.

[Sinjinhawke]

I have a (mostly working) 600xl with a similar issue.  SDRIVE seems to be invisible to the SIO.  When I try to load from the 1010 it will send the command to start it turning but it always fails to load (don't have any other SIO devices to try). 

 

The RF output is very garbled but it's not the RF cable as using the same cable on my 800xl is quite good (for RF). 

It's my childhood machine so I want to fix it up but keep it as stock as possible since I have working 800xl and 130xe (and non-working 600xl) to tinker with.

 

I did have the original 600XL Atari power supply go bad so it's possible it damaged something because before that the video was fine (for RF).

 

I'll have to try some of these suggestions as well.  Love the advice on these forums.

[+DrVenkman]

8 minutes ago, Sinjinhawke said:

I have a (mostly working) 600xl with a similar issue.  SDRIVE seems to be invisible to the SIO.  When I try to load from the 1010 it will send the command to start it turning but it always fails to load (don't have any other SIO devices to try).

The cassette MTR control line is sent via the 6520 PIA chip. Most of the rest of the serial I/O stuff, and all the signals needed for disk drive emulation by your SDrive, are sent via POKEY. That is probably a clue to your issue. 

[Sinjinhawke]

12 minutes ago, DrVenkman said:

The cassette MTR control line is sent via the 6520 PIA chip. Most of the rest of the serial I/O stuff, and all the signals needed for disk drive emulation by your SDrive, are sent via POKEY. That is probably a clue to your issue. 

I do have a couple of POKEY's poking around.  It's mostly obstructed by a 1980's 64KB memory upgrade board but I should be able to get in there to remove it and plug in the POKEY from my other 600xl or 800xl.  130XE has no sockets.  Bad Atari.  BAD!!!! 

[Sinjinhawke]

1 hour ago, DrVenkman said:

The cassette MTR control line is sent via the 6520 PIA chip. Most of the rest of the serial I/O stuff, and all the signals needed for disk drive emulation by your SDrive, are sent via POKEY. That is probably a clue to your issue. 

You sir, please take a bow.  Popped in a different POKEY and the SIO now sees the SDRIVE2.  Looking at the old POKEY it appears the R/W I/O Control pin is corroded and broken off part way down.  Quite odd as none of the other pins show the corrosion.  I have never previously removed the chip.  Possible when the power supply fried it also cooked that one pin?

 

Now to solve the crappy RF.  Maybe the RF box is in need of maintenance or replacement with another option.  Also need to replace the keyboard connecter.  When I pulled out the keyboard some months ago it pulled out a few of the connectors with it.  Have replacement keyboard connectors coming from Europe eventually.  Been in transit for 3 months.  Should have paid for tracking.  /fail

 

[_The Doctor__]

so taking it out to clean it up was a good and revealing experience kudos job to both of you!

[JGRAHAM2]

On 3/6/2021 at 8:00 AM, JGRAHAM2 said:

Thanks, I will do this later today and report back here.

I checked the resistors and all look good. Continuity looks good. Voltages look good at the power board/mainboard connector.

[JGRAHAM2]

I looked at the schematics and there is not much between the SIO port and the PIA and POKEY chips. Some resistors and capacitors. The resistors check fine in circuit. Capacitors are harder to check, but they are not shorted. The power board/ mainboard connector looks good. I ran Super SALT, but I don’t have the test fixture or “SIO shorting plug”, which I assume is a loopback, does anyone have a wiring diagram for that?

[+kheller2]

Does it work with any stock gear like 810 or ?

[JGRAHAM2]

1 hour ago, kheller2 said:

Does it work with any stock gear like 810 or ?

I haven’t tried with a real drive yet. I did with a tape drive as I was working on one. It starts the tape, but fails to load.

[+DrVenkman]

9 hours ago, JGRAHAM2 said:

I haven’t tried with a real drive yet. I did with a tape drive as I was working on one. It starts the tape, but fails to load.

As i pointed out to another person with similar issues, the cassette MTR control line is handled by PIA. Everything used in disk access or any other serial I/O though an SIO2PC, SDrive-MAX, etc is via POKEY. 

[JGRAHAM2]

2 hours ago, DrVenkman said:

As i pointed out to another person with similar issues, the cassette MTR control line is handled by PIA. Everything used in disk access or any other serial I/O though an SIO2PC, SDrive-MAX, etc is via POKEY. 

Thanks, that is why I tested with the cassette recorder. I have verified that both Pokey and PIA are good based on switching them out with a spare board and testing there. (Spare board is an 800XL)

[+DrVenkman]

If you have a scope or logic probe, test for activity when inserted in the suspect machine. You may have a socket issue.

[JGRAHAM2]

I have both. I’ll try that.

[+DrVenkman]

9 minutes ago, JGRAHAM2 said:

I have both. I’ll try that.

When was restoring one of my 1200XL’s a few years ago, I discovered three sockets with one or more corroded or permanently-bent wipes. The first one I found, ID’D after painstaking checks of every connection on each chip versus a logic chart from SAM’s 800XL document, was the Phi2 connection for POKEY, which prevented the machine from booting. That socket wipe had broken clean off leaving just a stub to make intermittent connection at best. I found corrosion on a couple other pins in that socket and one or two wipes were bent and lacked spring tension. I found similar corrosion and bent wipes on both the SALLY and PIA sockets, though none of them had physically broken wipes. 

[JGRAHAM2]

I did find that the socket for the Pokey chip was as you described. The 28 pin would check good sometimes and sometimes not. It was clear that it lacked spring tension. I replaced it with a precision socket. It is acting different, but is still not working. Pin 28 is looking good now. I’ll work on it again tonight with the scope. I was looking at the field service manual on what I should see.

[+DrVenkman]

Pin 28 is SOD, Serial Output Data. Poor contact will definitely affect I/O operations but will have no impact on any other chip functions. Good luck tracking down the rest of the issues.