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wyerd

HOW TO replace PEB PSU with new AT/LPX PSU

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As you may know, I managed to blow the 30 year old PSU in my NOS PEB http://atariage.com/forums/topic/233880-corcomp-rs232-card-killed-my-peb-help/ and it was suggested that it could be replaced with a newer AT or ATX PC type PSU as Tursi had done http://www.harmlesslion.com/text/atx_peb.htm .

 

I decided on the AT/LPX type which is available from Newegg http://www.newegg.com/Product/Product.aspx?Item=N82E16817338010&cm_re=at_psu-_-17-338-010-_-Product as it came with the same type of switch on my PEB and it was reasonably priced.

I also ordered a Molex power extension lead http://www.newegg.com/Product/Product.aspx?Item=N82E16812196873 ,

a Noiseblocker fan http://www.frozencpu.com/products/8403/fan-520/Noiseblocker_NB-BlackSilentFan_X1_80mmx25mm_Ultra_Quiet_Fan_-_1300_RPM_-_10_dBA.html?tl=c15s58b160

and a Molex to internal fan connector http://www.ebay.com/itm/261510776579?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT .

 

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PSU came with 4x HDD type Molex connectors, 2x FDD connectors, the P8 and P9 type power connectors and push button power switch.

 

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Molex to fan connector.

 

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I thought it best to bench test the PSU connected to the fan to make sure that it worked before I took it apart as there were a number of reviews on the Newegg site that had DOA units. No issue with this one.

 

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I then came across my first problem. The new switch doesn't have the side mounting as the old one does, so I had to come up with a solution as I couldn't use the old one......

 

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The power cables are soldered to the switch which unfortunately came apart. I suggest using the old switch if possible, especially with the newer rocker switch type as it saves another issue I had later on.

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I figured out that flattening out one side of the old switch bracket may solve the problem.

 

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I had to file a large chunk as it got in the way of the spring.

 

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Fitted. Would it match up with the hole in the case? Initial tests looked ok, but as the case wasn't screwed together, I could only find out once the new PSU was properly in place.

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img_1321.jpg

 

I had to remove the 120v out connector which also involved de-soldering the cables from the circuit board

 

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Circuit board removed

 

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I then de-soldered the fan and the Live & neutral cables.

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I then soldered the brown cable from the switch to the Neutral (the old white cable) and Blue cable from the switch to the Live (the old black cable) circuits on the board.

Edited by wyerd

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By this stage I'd removed the old PSU, fuse, fan and power connector from the PEB. I won't be going into how I did here as instructions are available on MainByte.

 

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I utilized the bolts left by the old transformer to attach the circuit board holder to. Also installed the power connector from the new PSU.

 

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Cable ties were then used to attach the board to the holder.

 

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A quick test using the case fan connected to the Molex connector. It works! :thumbsup:

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IMG_1333.JPG

 

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I decided to use disconnect connectors for the power wiring to the PEB board as it'll be easier to replace the PSU in future. The PEB green and brown wires are connected together. The power from the PSU are connected to the old PEB wiring as follows :-

PEB    Voltage   AT PSU   Voltage
Black  Ground    Black    Ground
Green   +8v      Yellow    +12v
Brown   +16v     Yellow    +12v
Yellow  -16v     Blue      -12v

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Connected up to the new PSU wiring. I used the cables from the P8 connector.

 

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Cabled tied up. The red cables on the left are for the 120/240v switch which is tidied out of the way. Note the bent heat sink - not done by me!

 

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When the PEB was re-assembled, the question about whether the power switch would line up was answered - NO..........

 

To be continued.....

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Do you mind if I ask a couple of followup questions?

 

1) Did the switch work out perfectly after everything was all buttoned up?

2) What are you going to do with that hole from the fuse holder? Eventually jumper another holder down there or use it for another purpose like a USB power port?

 

** EDIT ** Never mind on question one... you posted that while I was composing my post.

Edited by --- Ω ---

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There is a plastic spacer/insulator between the switch and the metal mounting, so I figured that the newer switch is better insulated and didn't need it and without it might position the switch better. So out it came.

 

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A couple of capacitors got in the way when I re-assembled the PEB, but luckily it's flexible enough to move the obstruction out of the way.

 

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The switch is now spot on target.

 

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Once all the cards and drive were inserted back into the PEB and connected to the console, it was the moment of truth! It all appears to work.....PHEW!! This was late last night so I've still got to use it and I haven't tried the CompCard yet. I've left the fuse holder slot empty as nothings going to get inside. I may cover it with tape or leave it for extra ventilation. The fan is soooooooo quiet, I thought it wasn't on at first until I checked that it was actually spinning.

Edited by wyerd
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Lessons learnt :- Don't blow the PSU in the first place!!!! It is possible to use a newer PC type PSU to replace the old one, but I'd recommend keeping the old switch by cutting the cables to the old PSU. Leave 3 inches of cable and then crimp the ends with disconnect connectors which can now slot in place of the newer switch.

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Are you going to arrange some sort of cover for the new PSU board? If you have the PEB apart again and accidentally put your pinkies in the wrong place, a PC PSU can give one hell of a jolt, even if it's been switched off for a while.

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Are you going to arrange some sort of cover for the new PSU board? If you have the PEB apart again and accidentally put your pinkies in the wrong place, a PC PSU can give one hell of a jolt, even if it's been switched off for a while.

I hadn't planned on it. I'll just have to keep your advice in mind the next time I have the PEB apart. Covering it could also cause ventilation issues I would have thought.

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Do you have any cards in the PEB without clamshells? If so, be sure the 5v regulators have heat-sinks or the higher voltage will take its toll on them. The Horizon RAMdisks, IDE card, and SCSI card are a few cards that are inserted into the PEB without shells that you may want to inspect.

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Do you have any cards in the PEB without clamshells? If so, be sure the 5v regulators have heat-sinks or the higher voltage will take its toll on them. The Horizon RAMdisks, IDE card, and SCSI card are a few cards that are inserted into the PEB without shells that you may want to inspect.

Thanks for the warning. I have the Flex Connector card, 8x32 memory and Disk Drive Interface cards installed all with shells. I still have the CorComp RS232 to install which has a thin shell.

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Thanks for the warning. I have the Flex Connector card, 8x32 memory and Disk Drive Interface cards installed all with shells. I still have the CorComp RS232 to install which has a thin shell.

The thin shell should be metal and more than sufficient. Some of the shells had spacers (plastic washer?) to contend with. I don't recall whether a metal washer is necessary to ensure full contact between the shell and the regulator "fin" containing the screw hole.

 

If this is the RS232 that took the power hit, verify that neither the regulator input nor output are shorted to ground. You can do this by checking between ground and the input/output legs. Hopefully the RS232 didn't take a hit to a buffer chip or 9901.

 

Others may also chime in with related thoughts, so perhaps give it a day or two before you put that card back into the box. :)

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The thin shell should be metal and more than sufficient. Some of the shells had spacers (plastic washer?) to contend with. I don't recall whether a metal washer is necessary to ensure full contact between the shell and the regulator "fin" containing the screw hole.

 

If this is the RS232 that took the power hit, verify that neither the regulator input nor output are shorted to ground. You can do this by checking between ground and the input/output legs. Hopefully the RS232 didn't take a hit to a buffer chip or 9901.

 

Others may also chime in with related thoughts, so perhaps give it a day or two before you put that card back into the box. :)

 

OK. I'll check out the RS232 card - thanks for the tip. I'll hang back a few days before plugging it in, although I may have a memory issue to sort out first http://atariage.com/forums/topic/234402-ram-errors-using-ti-diagnostics-on-extended-basic-v27/

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The QUEST 512K RAMdisks had a pitifully small heat sink as issued. A bit of aluminum (or aluminium) sheet cut and then bent over the battery pack with a bit of clearance provided an excellent heat sink. Don't forget the conductive grease!

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