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Need help: 1200XL no SIO (Won't read disk or SIO2SD)


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#1 ACML OFFLINE  

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Posted Sun Mar 4, 2018 8:26 PM

First let me say that yes, I've replaced R63 with a jumper. Everything seems fine (video, sound), but it won't recognize my SIO2SD.  Actually tried multiple SIO2SDs on it without success.  Tested those SIO2SDs on other 1200XLs and they work.  I swapped the PIA (6520) and not change.  I swapped the POKEY and no change.  I swapped the 6502C and no change.  The LCD on the SIO2SD lights up and I can see the file in D1: on the SIO2SD LCD display, just no load.  The fact that the SIO2SD displays both lines on the lighted LCD display tells me its getting power.  It powers up pretty reliably, but always as if nothing is plugged into the SIO port.  Once in 20 tries it did boot to black screen.  

 

I would be greatly appreciative if someone has any guidance on what might be causing this.  I've modified and fixed scores of Atari's over the years, but never encountered this particular issue.

 

 

 



#2 Nezgar ONLINE  

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Posted Sun Mar 4, 2018 8:29 PM

How about with a real disk drive? Can you measure the 5V voltage coming out of the SIO ?

#3 DrVenkman OFFLINE  

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Posted Sun Mar 4, 2018 8:35 PM

Bad connection at one or more pins in the POKEY socket? 



#4 ACML OFFLINE  

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Posted Sun Mar 4, 2018 8:40 PM

How about with a real disk drive? Can you measure the 5V voltage coming out of the SIO ?

I don't have a real disk drive anymore, but I just verified 5.01 VDC on pin 10 of the SIO.



#5 ACML OFFLINE  

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Posted Sun Mar 4, 2018 8:41 PM

Bad connection at one or more pins in the POKEY socket? 

Would removing the POKEY and testing continuity from the top socket side to bottom board side identify an issue like this?  Isn't the PIA mainly for disk IO?


Edited by ACML, Sun Mar 4, 2018 8:42 PM.


#6 DrVenkman OFFLINE  

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Posted Sun Mar 4, 2018 8:46 PM

Would removing the POKEY and testing continuity from the top socket side to bottom board side identify an issue like this?

 

Not necessarily. If the wipes in the socket are getting bent/worn from age, they might just not be making good contact with all 40 legs of the chip when inserted into the socket. I did a video last year showing how one pin on the POKEY socket in my 1200XL was causing issues. Replacing the socket fixed the issue. 

 

​This isn't a great video from a production standpoint, but shows how lost spring tension in a single wipe of the socket can affect a machine:

 



#7 Nezgar ONLINE  

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Posted Sun Mar 4, 2018 9:17 PM

Random thought... how about oxidization on the SIO pins maybe reducing contact on some I/O pins just enough. Maybe getting in between all the pins with a qtip or smaller and isopropyl alcohol.



#8 ACML OFFLINE  

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Posted Sun Mar 4, 2018 9:24 PM

 

Not necessarily. If the wipes in the socket are getting bent/worn from age, they might just not be making good contact with all 40 legs of the chip when inserted into the socket. I did a video last year showing how one pin on the POKEY socket in my 1200XL was causing issues. Replacing the socket fixed the issue. 

 

​This isn't a great video from a production standpoint, but shows how lost spring tension in a single wipe of the socket can affect a machine:

 

 

I removed the PIA and POKEY and all the wipes looked like they still would make good contact.  There is one thing about this board.  I bought the machine off eBay and it came with a power supply, except it was a power supply for a 5200.  That's 9VDC not 9VAC.  So, I assume the person may have run or tried to run the 1200XL on this supply.  Could that have damaged something?  I noticed it was the wrong kind of supply immediately and I never tried to use it.  Also, I upgraded the video with ClearPic 2002 and upgraded the OS with two 27128s.  It now has the 600XL/800XL OS and the Omniview OS.  I use the channel select as an OS selector switch.  I've done these same mods on a dozen machines and they have never caused an issue so I think its not that.  When I do the mods (OS and ClearPic), I usually only power check the units so I don't know if it would have done this before the mods.  I suspect it would have. 


Edited by ACML, Sun Mar 4, 2018 9:28 PM.


#9 _The Doctor__ ONLINE  

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Posted Mon Mar 5, 2018 4:10 PM

9 vdc could have .... check for clean power both 5 and 12...


Edited by _The Doctor__, Mon Mar 5, 2018 4:10 PM.


#10 DrVenkman OFFLINE  

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Posted Mon Mar 5, 2018 4:18 PM

I don't really know if the power supply would have damaged anything. The 1200XL has a two-stage power system inside - first, a large rectifier converts the expected 9VAC into 12VDC, and then a pair of 7805's convert that from 12VDC to 5VDC. What does a rectifier do when it gets a DC current rather than the AC current it expects?



#11 _The Doctor__ ONLINE  

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Posted Mon Mar 5, 2018 4:27 PM

only half the circuit is energized starving the doubler slightly, can cause slight under voltage and heat issues, brown out conditions if you will on low mains days... sometimes not enough current.


Edited by _The Doctor__, Mon Mar 5, 2018 4:28 PM.


#12 BillC OFFLINE  

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Posted Mon Mar 5, 2018 5:35 PM

only half the circuit is energized starving the doubler slightly, can cause slight under voltage and heat issues, brown out conditions if you will on low mains days... sometimes not enough current.

The 1200XL only uses +5VDC, no voltage doubler circuit.



#13 ACML OFFLINE  

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Posted Mon Mar 5, 2018 7:20 PM

The 1200XL only uses +5VDC, no voltage doubler circuit.

Yes, no 12 VDC on pin 12 of the SIO.  I think the 400/800 needed 12 VDC for the 16K RAM chips.  Not sure what to do next.  It's not the PIA or POKEY.  Is there other low hanging fruit (swap a chip) I should look at.  Like TTL 74 series chips?



#14 tf_hh OFFLINE  

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Posted Tue Mar 6, 2018 1:31 AM

First let me say that yes, I've replaced R63 with a jumper. Everything seems fine (video, sound), but it won't recognize my SIO2SD.  Actually tried multiple SIO2SDs on it without success.  Tested those SIO2SDs on other 1200XLs and they work.  I swapped the PIA (6520) and not change.  I swapped the POKEY and no change.  I swapped the 6502C and no change.  The LCD on the SIO2SD lights up and I can see the file in D1: on the SIO2SD LCD display, just no load.  The fact that the SIO2SD displays both lines on the lighted LCD display tells me its getting power.  It powers up pretty reliably, but always as if nothing is plugged into the SIO port.  Once in 20 tries it did boot to black screen.  

 

I would be greatly appreciative if someone has any guidance on what might be causing this.  I've modified and fixed scores of Atari's over the years, but never encountered this particular issue.

 

Regarding all the points you´ve already checked, IMHO the only reason could be a broken trace OR defect discrete part in line of COMMAND, DATA_IN or DATA_OUT. Do you have a scope? Then it should be really easy to find out the issue. COMMAND line should toggle sometimes to low during "detection SIO sound" after powering on. Also the DATA_OUT line should have some transistions, the O.S. sent "Status" to Drive D1: to test if there´s any. When the display of your SIO2SD doesn´t change during the "buzzing SIO sound", then COMMAND or DATA_OUT is mailfunctioned.

 

Here are the parts to check:

 

COMMAND-Line: R79 (100 ohms) and capacitor C82.

DATA_IN: R127 (100 ohms) and capacitor C90. Also R41 (4.7k pull-up to +5V).

DATA_OUT: R128 (100 ohms) and capacitor C91. Also R42 (4.7k pull-up to +5V).

 

The caps mentioned are connected to ground. So if the signal is constantly at low level, the corresponding cap should be exchanged (1nF) or removed for test - works also without.

 

If you don´t have a scope, check voltages in idle state. All three lines should have something over +4.5 volts. If not, check all parts listed above. And also examine the traces.

 

Good luck, Jurgen



#15 tf_hh OFFLINE  

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Posted Tue Mar 6, 2018 1:32 AM

Yes, no 12 VDC on pin 12 of the SIO.  I think the 400/800 needed 12 VDC for the 16K RAM chips.  Not sure what to do next.  It's not the PIA or POKEY.  Is there other low hanging fruit (swap a chip) I should look at.  Like TTL 74 series chips?

 

There´s no 12 volts used in a 1200XL. Only the 400 and 800 computers have 12 volts at the SIO connector, all other computer´s not.



#16 tf_hh OFFLINE  

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Posted Tue Mar 6, 2018 1:39 AM

That's 9VDC not 9VAC.  So, I assume the person may have run or tried to run the 1200XL on this supply.  Could that have damaged something?

 

No, not possible to damage anything when VDC is used but VAC is required - the opposite way can damage a lot of things for sure :grin:

 

When the power circuit doesn´t really need VAC, then the most devices fed with VAC can also be used with a VDC power supply - the VDC must be 1.4 times higher than the VAC required. So when 9 VDC is used, the effective transformed voltage at the 7805 regulators maybe to low - the computer won´t start. But nothing can be destroyed.



#17 _The Doctor__ ONLINE  

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Posted Tue Mar 6, 2018 10:03 AM

Yes, no 12 VDC on pin 12 of the SIO.  I think the 400/800 needed 12 VDC for the 16K RAM chips.  Not sure what to do next.  It's not the PIA or POKEY.  Is there other low hanging fruit (swap a chip) I should look at.  Like TTL 74 series chips?

No my 1200XL's have the 12 volt line and the 5 volt line fixed... because we like to have it all... and because we wanted other things that worked on the 400/800 to work on the 1200...

namely voicebox but other items like 12 volt as well.

I bet the modifications are posted on Atari Age ;)

 

and operating computers under low voltage or starved for current can slowly damage them... so say what you want, it is very much the truth.


Edited by _The Doctor__, Tue Mar 6, 2018 10:04 AM.


#18 ACML OFFLINE  

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Posted Tue Mar 6, 2018 4:46 PM

No my 1200XL's have the 12 volt line and the 5 volt line fixed... because we like to have it all... and because we wanted other things that worked on the 400/800 to work on the 1200...

namely voicebox but other items like 12 volt as well.

I bet the modifications are posted on Atari Age ;)

 

and operating computers under low voltage or starved for current can slowly damage them... so say what you want, it is very much the truth.

I thought the 1200XL only had two 7805 regulators?  Where would the 12 VDC come from?



#19 ACML OFFLINE  

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Posted Tue Mar 6, 2018 4:49 PM

 

Regarding all the points you´ve already checked, IMHO the only reason could be a broken trace OR defect discrete part in line of COMMAND, DATA_IN or DATA_OUT. Do you have a scope? Then it should be really easy to find out the issue. COMMAND line should toggle sometimes to low during "detection SIO sound" after powering on. Also the DATA_OUT line should have some transistions, the O.S. sent "Status" to Drive D1: to test if there´s any. When the display of your SIO2SD doesn´t change during the "buzzing SIO sound", then COMMAND or DATA_OUT is mailfunctioned.

 

Here are the parts to check:

 

COMMAND-Line: R79 (100 ohms) and capacitor C82.

DATA_IN: R127 (100 ohms) and capacitor C90. Also R41 (4.7k pull-up to +5V).

DATA_OUT: R128 (100 ohms) and capacitor C91. Also R42 (4.7k pull-up to +5V).

 

The caps mentioned are connected to ground. So if the signal is constantly at low level, the corresponding cap should be exchanged (1nF) or removed for test - works also without.

 

If you don´t have a scope, check voltages in idle state. All three lines should have something over +4.5 volts. If not, check all parts listed above. And also examine the traces.

 

Good luck, Jurgen

Thanks Jurgen,

            I don't have a scope, just a cheap multimeter from Radio Shack. Are  you saying I need to see ~4.5 volts at those five resisters and three caps?  So, if I see an "open" (i.e. 0 volts), that is the trace that I should track down?



#20 DrVenkman OFFLINE  

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Posted Tue Mar 6, 2018 5:00 PM

I thought the 1200XL only had two 7805 regulators?  Where would the 12 VDC come from?

 

The 12VDC comes from the rectifier; it takes the 9VAC, outputs 12VDC to the hot side of the two 7805's. 



#21 ACML OFFLINE  

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Posted Tue Mar 6, 2018 7:32 PM

 

The 12VDC comes from the rectifier; it takes the 9VAC, outputs 12VDC to the hot side of the two 7805's. 

O.K..  So does that mean I should be getting 12 VDC on pin 12 of the SIO?  I am getting 5 VDC on pin 10, but nothing on pin 12.



#22 DrVenkman OFFLINE  

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Posted Tue Mar 6, 2018 7:34 PM

O.K..  So does that mean I should be getting 12 VDC on pin 12 of the SIO?  I am getting 5 VDC on pin 10, but nothing on pin 12.

 

Not unless you run the current there yourself. IIRC, that pin isn't connected on the 1200XL. And the +5VDC pin is crippled with a current-limiting resistor at R63 (I've replaced R63 on my machines with 1 ohm jumpers).



#23 ACML OFFLINE  

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Posted Tue Mar 6, 2018 8:21 PM

So pins 3 (data IN), 5 (data OUT) and 7 (COMMAND) seem to be the SIO pins I need to interrogate activity on.  Can I tell anything with a cheap Radio Shack multimeter?  In an idle state, since they are all active low, should I be able to see ~5 VDC on these three pins?


Edited by ACML, Tue Mar 6, 2018 8:25 PM.


#24 _The Doctor__ ONLINE  

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Posted Tue Mar 6, 2018 8:41 PM

I use diodes type and value I've posted posted elsewhere... instead of the direct jumpers... for the 12v and 5v sio lines...

also if the sio port has the sio sealing current stabilize mod for hisio... that would change what you see.

you can see voltage fluctuate with a logic probe, sio2pc device led... scope...etc... during the boot/polling period at startup

depends your meter if it's quick enough to see anything else


Edited by _The Doctor__, Tue Mar 6, 2018 8:45 PM.


#25 ACML OFFLINE  

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Posted Tue Mar 6, 2018 9:23 PM

I've narrowed the issue to pin 5 of the SIO port (data OUT).  At idle on a good working 1200XL, I get get 5 VDC on pins 3,5 and 7 on the SIO port.  On this particular board, I get 5 VDC on pins 3 and 7, but an "open" on pin 5. Now to track down that run using the information Jurgen provided for data OUT.

 

DATA_OUT: R128 (100 ohms) and capacitor C91. Also R42 (4.7k pull-up to +5V).

 

O.K., now I'm officially confused.  Both R128 and C91 have 5 VDC on both sides (great).  Now R42 was not measuring 4.7K ohms (installed) and I got 5 VDC on the side next to the 6502C, but did not get 5 VDC on the other side of the resistor. I verified on a good 1200XL that R42 measures 4.7K ohms (installed).  I replaced R42 with a new 4.7K ohm resistor, but when I put the multimeter to it, it shows 276 ohms (installed)???  I'm putting the two leads on both sides of the resistor (installed).  I verified with the ohm meter before I installed the new one that it is indeed a 4.7K ohm resistor.  I'm an Aerospace guy, not a EE, so my knowledge is limited here.  Wouldn't there have to be another resistance in parallel to make the 4.7K ohm resistor read 276 ohms?  

 

Also, after I removed the old resistor, I measured it uninstalled and it shows 4.7K ohms.  So the original resistor was good???  So, the difference on the bad board is that something is causing R42 to show 276 ohms instead of 4.7K ohms that a good board shows.


Edited by ACML, Tue Mar 6, 2018 10:14 PM.





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