Compaq Deskpro EN PSU

[stevo1210]

Hello,

I have recently aqquired a Compaq Deskpro 933MHz computer. It is Small form factor and it wont boot at all.
The caps on the motherboard are LXG, Panasonic and two Teapo caps.
The person that gave it to me said that the power supply died. I cant determine that. The motherboard has no burn marks or bad caps anywhere, no damaged traces, nothing that would indicate a dead board.
The power supply on the other hand has a bit of rust on the casing and a fuse (240V 5A) which has turned black in the glass center. The power supply has Rubycon YXG caps and look fine, so i doubt caps.
The power supply circuit board looks fine, no burn marks anywhere or shorts as far as i can see.

I doubt a power surge either because the person lives a few blocks away and we have the same power source (except his power line is underground) and ive never had a surge, so neither should he.... He also has a surge board.

There are absolutely no burn marks anywhere in the PSU or on the motherboard to indicate a surge.


Am i able to confirm that the PSU is dead?.... just before i waste $35AUD on a new power supply only to find a dead board too?.

Apparently the power supply is only 14 pins? and it says series PDP-115.


Thank You.

[PeteS in CA]

Re: Compaq Deskpro EN PSU

... a fuse (240V 5A) which has turned black in the glass center ...

It's blown (rather violently, given that the metal of the fuse wire sprayed the inside of the glass). With the P/S unplugged, use an ohm meter to check whether one of the I/P 'lytic caps (or MOVs) or a switch device is shorted. Also, if your power is 230VAC but the P/S is set for 115VAC, that will result in a blown fuse, possibly with some damage to the components mentioned above.

[stevo1210]

Re: Compaq Deskpro EN PSU

I tried a brand new fuse and then i plugged the PSU into the wall without it being connected to any motherboard etc. and then there was a large boom that came out of it, and it smelled foul. So i obviously opened it back up and saw the fuse again, turned black with the glass middle sprayed black. Any ideas to what caused this? i suspect the transformer unit because that stinks the most.

[stevo1210]

Re: Compaq Deskpro EN PSU

And also, yes it was on 230V at the red switch.

[PeteS in CA]

Re: Compaq Deskpro EN PSU

Check the TO-220 or TO-247 (unsure of package type) switch devices that are on the side of the primary-side heatsink. If they are on the side facing the main transformer, one or both probably blew, stinking up the area around the main transformer. Unless you are techie and have access to a DMM, an oscilloscope and electronic components, I think a new P/S might be the way to go. If the fan is still good, it might be worth salvaging.

[stevo1210]

Re: Compaq Deskpro EN PSU

Here are the internal pictures of the "dead" Compaq Power supply.... could someone please tell me what components to look for which are probably dead?
All i can guess thats dead is that "Lite ON" transformer unit since that area stinks like burnt plastic.... you can see that fuse turned black in one of the images....

[kc8adu]

Re: Compaq Deskpro EN PSU

the mov's near the input caps are burnt.
see the splatter on the board and heatsink?

[arneson]

Re: Compaq Deskpro EN PSU

I fixed one of those odd shaped power supplies in a gateway years ago.
I noticed those compaqs are selling for less than the cost of a power supply.

[stevo1210]

Re: Compaq Deskpro EN PSU

Lookie what we have here....

Well.... now i have been game enough to open the power supply up completely, and i actually found 2 components which were charred completely black and also cracked! , it looks to be like a ceramic capacitor or similar.... sorry im quite new to the world of electronics.
could it be a MOV like kc8du said?
well i want to know what this component is and what its value is so i can go and buy one, unfortunately it's wrapped in some rubber sleeve.
I looked at the heatsink into those mosfets and the white stuff is just heatsink paste. Theres some factory glue residues which are grey stuck onto the circuit board.

In the pictures, it's that component in between the Rubycon caps.... the Rubycons look fine except for a bit of smoke on the sides of them from which "this component" spattered on. Theres also a little bit of black smoke residue on the circuit board.

[starfury1]

Re: Compaq Deskpro EN PSU

I would follow PeteS and Kc8du advice (me still grasshopper on this) there are others that can offer good advice too, I know

Those components would be stuffed from the looks of it and if the are short most likely why you fuse is blowing.
They are covered in heatshrink by the looks of it
You would need to replace with suitable types
I cant help you with what values you need to replace

abit on MOV's here

You are working on a part of the circuit which is directly connected to the mains supply (PeteS 240 V AC RMS)
(ideally working with isolation transformer (1:1 240V/240v) and maybe the old TV tech's trick of a light bulb in series..don't know if this is accepted practice though)

I would be checking for other damages as PeteS outlined, rather then risk frying other components.

Those 2 ruby caps can still possibly hold a charge and give you a good belt so be careful.

Maybe best idea is just get another psu.....as this seems to be the problem


To get a better idea of what your working on check the forum here
and here

If you lucky maybe those 3 components have done there job of protecting the psu.

You may also want to track down a PDF on the chip used to get a better idea of how it being used in this psu.

Hope it helps Good luck and be careful

[kc8adu]

Re: Compaq Deskpro EN PSU

i would remove the mov's and check for a shorted bridge.
if ok replace fuse and try it.
many cheapie psu dont have those parts anyway.
if it runs then track down replacements.

[PeteS in CA]

Re: Compaq Deskpro EN PSU

Yep, you've got two fried MOVs, and they may have failed short circuit (or low resistance). If the P/S was set for 115VAC and turned on into 240VAC, that could result, and the damage is permanent even if the P/S is reset to 230VAC. If that mistake didn't happen, there is another mechanism that could cause a failure. MOVs are used to clamp power line surges and spikes. And they are fast and handle quite a bit of energy. Unfortunately, every time they clamp a surge, they suffer a little bit of damage. With a lot of surges and spikes, MOVs gradually deteriorate until they conduct even with normal line voltages and fry themselves. Of course, it is possible that a really big surge with lots of energy might have exceeded the MOV's energy capability, frying it with one surge.

If you are techie and have test equipment, you can remove the fried MOVs (desolder or clip out) and check for other damage. If not, I suggest getting a new P/S.

[linuxguru]

Re: Compaq Deskpro EN PSU

It's probably fixable - you'll need a couple a 9D431K or similar MOVs, and maybe a new primary bridge rectifier. If the fuse still keeps blowing after replacing these, the primary switching transistors are also gone.

[starfury1]

Re: Compaq Deskpro EN PSU

Thanks guys for filling in the blanks

cheers

[stevo1210]

Re: Compaq Deskpro EN PSU

Thank you to everyone that has contributed to this thread.... Ive decided this PC wasnt worth the fix so it's gone to a friends place. He probably can figure on fixing this stuff.... I havent got the time.... Im caught up in studies and all that now.

[stevo1210]

Re: Compaq Deskpro EN PSU

Today I went over to my friends place for a visit and I saw my old Compaq sitting in the corner with a layer of dust on top of it. I'm currently fixing a batch of DEER and Dell PSUs here so I decided to take this Compaq back home.
I had a closer look at the blown MOVs and I guess that yes, someone probably did use the red self destruct button on the back and switched it from 240V to 110V.
I also think the motherboard is dead, but I can get a replacement on eBay for $13AUD, so it isn't a big concern. The secondary side of the PSU looks fine, nothing burnt etc.
The caps still look fine.... well.... it could be because they are Rubycon caps....
The transformer doesn't look burnt and the transistors/ MOSFETs attached to the heatsink don't look burnt or melted either.

I really want to get the unique 14pin PSU working again, what will I have to replace apart from the MOVs and the blown fuse?? I will probably use parts from some dead Seventeam and Delta PSUs I have here.

Also about 8 months ago when I last tested this PSU to see if it still had life in it. As soon as I plugged it into the powerpoint without the motherboard attached etc. and then switched it on, the fuse blew and emitted a smell of burnt plastic and smoke.

Thanks.

[linuxguru]

Re: Compaq Deskpro EN PSU

If you're very lucky, nothing except the MOVs and the bridge rectifier would have blown. With a bit of bad luck, the primary switching transistors, and/or primary caps could also have blown. If you're really unlucky - a bunch of small passives in the base drive circuit for the primary switching transistors would also have blown.

It's probably more worthwhile to try to revive the Seventeam/Delta PSUs.

[999999999]

Re: Compaq Deskpro EN PSU

Your MOV is burnt, ought to be replaced, but may not be dead yet, it's failing would not blow the fuse (typically) and it is not the primary failure point. So yes, you ought to replace it but it's not the main problem.

I think your switching transistor is blown. I doubt the bridge rectifier is (but if you needed to later, you could still check it on your DMM).

On this picture,
https://www.badcaps.net/forum/attach...achmentid=4287
pull off (desolder first of course)) the part screwed to the leftmost heatsink, get it's datasheet from the markings on it,
http://alldatasheet.com/
and check it with a DMM as shown here,
http://www.allaboutcircuits.com/vol_3/chpt_4/3.html

If you are not confident you have identified the part, used an appropriate replacement part, don't even power it on again. Remember your safety is more important than (anything, but in this case...) an old proprietary 933MHz system.

[999999999]

Re: Compaq Deskpro EN PSU

If there's some kid (or whoever) that likes to flip that 110/220V switch, you could just take the switch out of the circuit (disable it). Typically when flipped to 110V, it closes the voltage doubling circuit but for 220V use it's open, meaning you could just completely remove either of the wires going from the switch to the PCB. Naturally this means it can't run in an 110V location anymore.

[stevo1210]

Re: Compaq Deskpro EN PSU

I unsoldered the MOVs the other day and cut the sleeves open. I also unsoldered the bridge rectifier.
I tried to dertermine what the markings are on the MOVs and the only problem is that it's covered in black soot so I am only guessing what it says.

This is what I can see on the MOV.
TVR?
10241?

There are two MOVs but the second one is burnt beyond recognition so I give up on that one.
The bridge rectifier also looks a little burnt on one of it's legs (far left on positive pole).
I only have one multimeter so I think I'll have to replace it anyway to be sure.

The text on the rectifier is:

CHINA
0124A
GBL08

Are the markings that I think are on the MOVs correct for a 240V circuit?

I think your switching transistor is blown.

I got the markings for the transistor on the leftmost heatsink. It says:

NEC
K3324
09

I'll probably need another one of these too.... I have a feeling that it's also blown.

Thanks.