Atari 800: No Power

[jaybird3rd]

I have an Atari 800 computer that I'm restoring, and I've replaced the power supply daughterboard with a new one from B&C ComputerVisions (I bought it about a year ago but am only now getting to use it). The new board will not power up at all, either connected to the mainboard or by itself. I'm not getting any voltage on the 5V or 12V pins going to the mainboard, but I know the AC adapter I'm using is good since it works with my 1200XL.

 

I've looked over the board and cannot see any blown/burnt components or damaged traces. My first guess would be that something is wrong with the voltage regulator(s), but since I am not experienced at troubleshooting these kinds of problems, I'm hoping that someone with more experience can offer some suggestions. Would would be the next step in troubleshooting?

 

Thanks in advance!

[sup8pdct]

I have an Atari 800 computer that I'm restoring, and I've replaced the power supply daughterboard with a new one from B&C ComputerVisions (I bought it about a year ago but am only now getting to use it). The new board will not power up at all, either connected to the mainboard or by itself. I'm not getting any voltage on the 5V or 12V pins going to the mainboard, but I know the AC adapter I'm using is good since it works with my 1200XL.

 

I've looked over the board and cannot see any blown/burnt components or damaged traces. My first guess would be that something is wrong with the voltage regulator(s), but since I am not experienced at troubleshooting these kinds of problems, I'm hoping that someone with more experience can offer some suggestions. Would would be the next step in troubleshooting?

 

Thanks in advance!

 

The 800 has 2 power switches, the main one on the side and the cartridge door interlock. Are you holding the cart one on?

 

James

[jaybird3rd]

Ugh ... I had a feeling it was something stupid I was overlooking! Yes, I did remember the cartridge door switch, and I had the cartridge door closed, but I had removed the black plastic piece from the interlock when I was cleaning the case, and I forgot to put it back in. Everything seems to be working fine now! Thanks!

Edited October 25, 2009 by jaybird3rd

[mimo]

heheheh, your not the first to forget that bit:twisted:

[atariksi]

Ugh ... I had a feeling it was something stupid I was overlooking! Yes, I did remember the cartridge door switch, and I had the cartridge door closed, but I had removed the black plastic piece from the interlock when I was cleaning the case, and I forgot to put it back in. Everything seems to be working fine now! Thanks!

 

I wonder if that switch can be turned on/off remotely (remote control).

[jaybird3rd]

Well ... perhaps I spoke too soon when I said that everything was working: I can't communicate with a real floppy drive or an APE cable through the SIO port. This problem is probably my fault: as I was reassembling the unit, I must have screwed on the RF shielding slightly wrong, because I think the bottom of a small copper clip on the front of the shield came into contact with the leads on some of the components on the mainboard (the long row of capacitors directly behind the keyboard connector). For a while I was only getting a "buzzing" sound instead of the traditional disk-polling "drumroll" sound on startup. This went away after I removed and reattached the shield, but there is still no response from the SIO.

 

I think I must have shorted out something on the mainboard because I also lost a row of keys on the keyboard at the same time, and I had to replace the 4051 multiplexers to get them back. The components the copper clip probably came into contact with were: the rear leads on capacitors C106, C108, C105, C115, C114, and C117. I've already tried replacing POKEY, but it didn't help. Does anyone happen to know any other ways of troubleshooting an SIO port? I'll try replacing the capacitors I listed above when I get back later tonight.

[sup8pdct]

Well ... perhaps I spoke too soon when I said that everything was working: I can't communicate with a real floppy drive or an APE cable through the SIO port. This problem is probably my fault: as I was reassembling the unit, I must have screwed on the RF shielding slightly wrong, because I think the bottom of a small copper clip on the front of the shield came into contact with the leads on some of the components on the mainboard (the long row of capacitors directly behind the keyboard connector). For a while I was only getting a "buzzing" sound instead of the traditional disk-polling "drumroll" sound on startup. This went away after I removed and reattached the shield, but there is still no response from the SIO.

 

I think I must have shorted out something on the mainboard because I also lost a row of keys on the keyboard at the same time, and I had to replace the 4051 multiplexers to get them back. The components the copper clip probably came into contact with were: the rear leads on capacitors C106, C108, C105, C115, C114, and C117. I've already tried replacing POKEY, but it didn't help. Does anyone happen to know any other ways of troubleshooting an SIO port? I'll try replacing the capacitors I listed above when I get back later tonight.

 

One important handshake line comes from the PIA chip (command). Maybe replacing it would help with your problem. Important lines on the sio port are pins 3,4,5,6,7,10. both 4 and 6 are gnd and 10 is +5v.

 

James

[jaybird3rd]

One important handshake line comes from the PIA chip (command). Maybe replacing it would help with your problem. Important lines on the sio port are pins 3,4,5,6,7,10. both 4 and 6 are gnd and 10 is +5v.

 

James

Thanks for that information. I checked the resistors and capacitors between Pins 3/5/7 and the chips, and they all seem to be fine. PIA seems to be fine, too, since replacing it didn't fix the problem.

 

One thing I do notice is that, when the SIO bus is idle, I'm getting a constant ~5V on Pin 3 (Data In) but no voltage on Pin 5 (Data Out). Shouldn't there be voltage on both pins unless the Atari is actively sending data?

Edited October 27, 2009 by jaybird3rd

[atariksi]

One important handshake line comes from the PIA chip (command). Maybe replacing it would help with your problem. Important lines on the sio port are pins 3,4,5,6,7,10. both 4 and 6 are gnd and 10 is +5v.

 

James

Thanks for that information. I checked the resistors and capacitors between Pins 3/5/7 and the chips, and they all seem to be fine. PIA seems to be fine, too, since replacing it didn't fix the problem.

 

One thing I do notice is that, when the SIO bus is idle, I'm getting a constant ~5V on Pin 3 (Data In) but no voltage on Pin 5 (Data Out). Shouldn't there be voltage on both pins unless the Atari is actively sending data?

 

You can set the Data Out pin to +5V or 0V with POKE 53775,3 and POKE 53775,131. See if that makes a difference on the voltage output.

[jaybird3rd]

You can set the Data Out pin to +5V or 0V with POKE 53775,3 and POKE 53775,131. See if that makes a difference on the voltage output.

No change. Still 0V, using both values.

[sup8pdct]

You can set the Data Out pin to +5V or 0V with POKE 53775,3 and POKE 53775,131. See if that makes a difference on the voltage output.

No change. Still 0V, using both values.

 

Hmmmm. the schematic has a pull up resistor on all pokey serial/clock lines. what happens to the serial lines when pokey is pulled out then powered on?

If it changes, bad pokey, if not, bad resistor, R290. it appears to be a resistor pack,4.7K.

 

James

[jaybird3rd]

Hmmmm. the schematic has a pull up resistor on all pokey serial/clock lines. what happens to the serial lines when pokey is pulled out then powered on?

If it changes, bad pokey, if not, bad resistor, R290. it appears to be a resistor pack,4.7K.

 

James

I'll give it a try later today. What's funny is, I tested the resistors in that resistor pack, and they all checked out at ~4.7K. Fortunately I have a spare, so I'll go ahead and replace it anyway.

[atariksi]

Hmmmm. the schematic has a pull up resistor on all pokey serial/clock lines. what happens to the serial lines when pokey is pulled out then powered on?

If it changes, bad pokey, if not, bad resistor, R290. it appears to be a resistor pack,4.7K.

 

James

I'll give it a try later today. What's funny is, I tested the resistors in that resistor pack, and they all checked out at ~4.7K. Fortunately I have a spare, so I'll go ahead and replace it anyway.

 

I think you should trace it from the POKEY pin (#28) for serial output to the SIO pin for data out (pin 5) and see where the +5V gets lost.