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11/73 not powering up

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zippysticks

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Nov 21, 2017
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Hi folks,

Just got a decommissioned 11/73 in a pedestal case with the BA23-A enclosure and H7864 PSU.
It won't power up so I'm looking for suggestions on what to try to help diagnose.

On pressing the front power button, the AC light illuminates inside the power switch, there is a momentary flash of the panel LED's and then nothing. Neither of the 10V chassis fans are spinning, no power to the installed cards or drives or front panel.

i KNOW the 0.22uF RIFA input filter capacitor has failed and is now open circuit as I removed its charred remains already and have a replacement on order.
This shouldn't affect PSU operation though right ?

The nearby 0.42uF capacitor is intact and looks fine but I'll replace that later anyway.

Anyone have a schematic for this PSU ?

Any suggestions what to try next please ?

Thanks
 
If it is the PSU I am thinking of I have never found an online schematic I am afraid. I will check the part number tomorrow though to make sure.

Dave
 
Thanks Dave. I guess they are supposed to be Field Replaceable Units., The system manual has this 'helpful' flowchart for diagnosis.
Simply leads to a decision to swap the PSU.

Screenshot 2023-06-23 at 20.32.38.jpg
 
Apparently its Astec supplied model number AA12131. So perhaps a little more hope of finding a diagram.

There seem to be quite a few repair of replacement services ranging from a couple of hundred dollars.

As always others have found this too link
 
Well, they'd want to get the customer back up and running ASAP so replacing the PSU makes sense. Then send it back for repair or whatever.
 
I hadn't realized there were places that still repair DEC gear. I could get my 11/83 CPU board repaired for $1000. Way too steep for me.
 
From reading that old thread, I'm not entirely sure the RIFA's are the problem. It would seem others have removed theirs entirely (not worried by any mains noise) and the machine still works.
 
I have partial schematics that I have reverse engineered. However, I am not an electronic engineer and so they will not be drawn logically and are highly likely to have mistakes too. But if you are interested I don't mind making them available.
 
Here is a zip of my schematics done with Eagle.
 

Attachments

  • H7864A.zip
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zippysticks said:
From reading that old thread, I'm not entirely sure the RIFA's are the problem. It would seem others have removed theirs entirely (not worried by any mains noise) and the machine still works.
Click to expand...
That is correct. The H7864 P/S in the BA23 will operate just fine without either of the RIFA caps on the AC line filter. The P/S will just be a little noisy electrically.

Note that there is a 3rd RIFA cap on another board in the P/S You will want to check it and probably replace it too. I'm not sure if that one can be removed without any affect. Also note that the one thread says the two caps are an X2 and Y2 - this is incorrect, though will cause no issues. But both are X2. Just make sure you DO get some combination since these are AC line filter caps you want to make sure if they fail, they fail in the proper way and don't cause a dangerous condition.
 
reinhardtjh said:
That is correct. The H7864 P/S in the BA23 will operate just fine without either of the RIFA caps on the AC line filter. The P/S will just be a little noisy electrically.

Note that there is a 3rd RIFA cap on another board in the P/S You will want to check it and probably replace it too. I'm not sure if that one can be removed without any affect. Also note that the one thread says the two caps are an X2 and Y2 - this is incorrect, though will cause no issues. But both are X2. Just make sure you DO get some combination since these are AC line filter caps you want to make sure if they fail, they fail in the proper way and don't cause a dangerous condition.
Click to expand...

Thanks and agree both are X2 - that useful YouTube video clearly shows them as X2.

@daver2 - It just so happens that the BA23 empty chassis I got from you last year has EXACTLY the same PSU that I know is working. So at least I have a replacement if I need it.
Have now pulled a muscle in my back lifting the chassis so not touching it again for a few days.
 
Sounds like the power supply outputs are shorted. I have seen this on my BA23. Try disconnecting the drives (one of them may have the motor jammed) and see if it comes up. Then try removing all the boards.
 
czunit said:
Sounds like the power supply outputs are shorted. I have seen this on my BA23. Try disconnecting the drives (one of them may have the motor jammed) and see if it comes up. Then try removing all the boards.
Click to expand...
Yep, already tried that thanks. I actually think its a problem in the PSU rather than in the load.
 
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