Delta DPS-150GB PSU failure

[powermax]

Hello crews,

I got a faulty Delta DPS-150GB PSU from a Power Macintosh G3 Beige.
The computer has suddenly stopped working.
I checked the PSU and found out that there is no voltage on the trickle rail. That explains why the Mac doesn't power on.

An initial visual inspection has revealed neither blown components nor bulging/leaking caps. The main fuse is good, too.

Judging by the markings on the PCB, the PSU was built in April 1998.
I therefore assume that replacing all caps except the big ones won't do any harm.

Nevertheless, I would like to ask the experienced users here for what can cause the trickle power to suddenly disappear. Is there any component I can check for failure?

Thank you in advance!

P.S.: I had to desolder C901 in order to determine its capacity because the marking was hidden by a huge blob of glue...

[Per Hansson]

Replacing all small electrolytic capacitors is certainly a good idea when the unit is 25 years old, it might just fix it.
One way to perhaps confirm that is to heat the unit up to ca 50°C or so, if it then starts you can be pretty sure it is the small caps.
But this does not always work if they are too far gone / completely dried out...

[powermax]

I have a device for measuring various components. It shows the following for the desoldered 100 uF cap (C901):

112,5 uF
ESR = .41 Ohm
Voss = 1,5 %

(see the attached picture)

I could measure all caps after desoldering. Would that be meaningful?

I have no possibility to heat up the PSU to 50° without risk of damaging the unit...

[Per Hansson]

Yes remove all small caps and test them but just a note: let them cool down to room temperature before measuring otherwise the data will be better than in reality (exactly like in the proposed heat test)

[powermax]

For 1 uF and 2,2 uF caps, my testing device measured the ERS > 2 Ohm.
The ERS of the other caps lays below 1 Ohm.

[sam_sam_sam]

Originally Posted by powermax

For 1 uF and 2,2 uF caps, my testing device measured the ERS > 2 Ohm.
The ERS of the other caps lays below 1 Ohm.

Can you please post the exact value of the 1uf and the 2.2uf thanks

Because if the value is over 1.5 ESR I question how good this capacitor is and the closer it gets 2 and over compared to a new one led me to change them anyway just for good measure but that just me personally

I also do a test with them @100*F then let them cool down to room temperature and to the temperature of your air conditioning vent which would be around 50*F or so if you get a result of more than 10% between these two results I would highly recommend that you replace them

[powermax]

Originally Posted by sam_sam_sam

Can you please post the exact value of the 1uf and the 2.2uf thanks

Markings: 1uF 50V
Measures: 948,1 nF, ESR = 2,4 Ohm, VLoss = 0,4 %

Markings: 1uF 50V
Measures: 938,2 nF, ESR = 2,2 Ohm, VLoss = 0,4 %

Markings: 2,2 uF 50V
Measures: 2180 nF, ESR = 2,1 Ohm, VLoss = 0,9 %

[powermax]

I'm looking for replacement caps. I have a couple of Chemicon KY ones and wanted to order more of the same kind but they seems to be discontinued by the manufacturer.

These look like a good replacement to me:

https://www.mouser.de/ProductDetail/...WCriJgLQ%3D%3D

https://www.mouser.de/ProductDetail/...S0Pc4Y1g%3D%3D

The difference is in the ESR. The former is rated at 900 mOhms while the latter is 400 mOhms.

Which one fits better?

[sam_sam_sam]

I would go with 50 volt ones not 25 volt ones

KY or KZE would be just fine I use them all the time if they are available

[powermax]

Originally Posted by sam_sam_sam

I would go with 50 volt ones not 25 volt ones

KY or KZE would be just fine I use them all the time if they are available

Well, the unit originally had three 25V and one 50V Rubycon caps.
Chemicon KY isn't available anymore. KYA 50V is a bit thicker - I need to check first if they fit into the available space.

KZE caps have a rated endurance of either 2000 or 10000 hours.
Rubycon offers 5000 hours as well...

[sam_sam_sam]

You could go with LXZ which both values are available in 25 volts ( and also available in 50 volt as well ) they automotive type capacitors I uses these quite often as well also LXY but not always available in all UF values

I have use both of them in switching power supply with no issues

I have to wonder if KY and KZE are being phased out for some reason because they are not very many UF values available anymore because I still have 1, 2.2 , 22 and other values as well still my in capacitor bin but getting low on some of them but they were bought ( a few years ago to more than several years ago )

because when I buy these low value capacitor I buy them 100 at a time that is why I still have so many still available in capacitor bin

[PeteS in CA]

I doubt that the caps used in that P/S were as low impedance as KY or KZE. LXV, PS (= PR), LXZ, or PW would probably do well for both output caps and smaller value decoupling and start-up caps.

That P/S predates 1A-3A 5VSB designs. You may have to draw your own schematic, possibly working your way back from the "Trickle" output wire (violet?). The IC mounted on HS1 may be part of that circuit.

[powermax]

Originally Posted by PeteS in CA

That P/S predates 1A-3A 5VSB designs. You may have to draw your own schematic, possibly working your way back from the "Trickle" output wire (violet?). The IC mounted on HS1 may be part of that circuit.

Is the schematic for a 1A-3A available somewhere?

[powermax]

It looks like the only series that offer 1 uF and 2,2 uF @ 50V caps is SMG (SMQ-E).
Okay to go with them?

[powermax]

I replaced 10 small electrolytic caps as suggested above. Then I plugged the power supply into the wall socket and checked the trickle pin with the meter. It showed 4.95V power.

I wanted to test the PSU without connecting it the motherboard. I found a post in the macrumors forum that describes how to turn this PSU on: one needs to wire the TRKL and the PowerON pins together.
The corresponding thread is here.

I connected the pins as described above but the PSU didn't start. The fan didn't spin on but the trickle power has disappeared.

It looks like the PSU is completely dead. The current situation is the same as earlier: nothing is visibly blown, the main fuse is still conducting power.

Is there anything I could do before throwing it away?