Gets power and fan spin. No POST

This is brilliant. And would make perfect sense. I was already thinking a short because it turns on right when power is connected. I literally checked the board power switch for resistance/continuity. But I wasn't convinced I was testing the right pins due to the way the switch is mounted, and never revisited it for some reason. I'm just so used to cell phones and laptops, and my brain wasn't making the translation.

This is just an iPhone VDD main short, but on a desktop computer. You exploded my brain.

I figured the PSU was blasting the fans because it was getting hot due to its own fault. But if there's a short... It's going full bore, dumping current into ground. I don't know why I didn't put two and two together.

I'm almost positive this is the board, but you're right, it's worth pulling everything and seeing if it still does it. And if it does I can find a board short. Hopefully, it's nothing god-awful and it’s just a bad cap.. I'm gonna drive my girlfriend nuts diode moding this thing at 11:30 at night.

@flannelist heyyy, did you manage to fix the board and/or find the issue? I have a hp z4 g4 doing the same thing 😬 would be nice if it isn't the cpu 😅 did yours beep and flash no cpu when you removed it?

@bazzaf I did not. This thing has become somewhat of a pet project (pretty much everything I fix these days outside work is a pet project). I got it in an offload of some machines from my job that we were just going to recycle so left the SSD at work for them to wipe and dispose and took the machine home. It just sits on my shelf until I can sort it and repurpose. Because this thing was too much of a beast to huck it.

I actually suspect really strongly in my case it's the PSU. I haven't tried uninstalling CPU for some reason, even though that was suggested.

I think I tried leaving RAM out, but not CPU. I can understand not wanting to replace that though. And I certainly don't have a spare CPU that will go in an LGA2066 socket to test. I suspect most people don't either.

@bazzaf WAIT do you have a multimeter? If so, we can try and cross compare PSU or any values really since nobody seems to have a pin out out posted anywhere. I was coincidentally looking at that on my shelf today wanting to poke at it so let me know.

@flannelist %100, I have a few multimeters, yes. 😊 im quite the hobbyist, one of which hobbys include some weird form of electrical engineering, mainly the form that doesn't like to throw away expensive things without trying far too hard, and spending far to much time on to try and fix it! When that fails, it's components get harvested and used in other diy electronic projects. 😆 I will open my psu up this week sometime, try to probe it as best I can and get back to you 👍

Somehow I missed this pin out in all of my searching. Thanks!

So couple follow up observations. When I plug in the PSU, but not connect it to the board, it spools up, but I only get power on the small connector (12V). Not sure if that's normal. It might just be.

I don't believe I checked pin voltages before I opened it. At least not without it being connected to the board since I wasn't even expecting it to power up with no board attached. I'll have to connect it today and see what I can find.

@flannelist I have not gone over the whole pinout I posted, but seems to be right compared to any other I've come across!

Interesting how yours acts when disconnected from the motherboard. Mine is the opposite, dissconnected from the motherboard, mains power connected and nothing happens, apart from the green light on the back illuminates. It might be that we have two different problems! I will find some time to do some more probing, and confirm some more of the pinout earlier posted.

@bazzaf Based on what I was finding on the PCB of the PSU, it may actually be that this PSU is 12V only. Most other PSUs I have seen are marked indicating other voltage rails. This one only has 12V marked anywhere I looked.

I actually thought initially that the PSU was the issue because it powers on when connected to mains, but the service manual actually calls out to remove the PSU from the computer and connect to power. "If the power supply fans turn on and the built-in self-test (BIST) light illuminates, the power supply is good and the power supply does not need to be replaced."

Now I feel like yours might be a power supply issue. But I am not sure mine is. I still think mine is a board short. Especially since it powers on as soon as I connect power (the whole computer, not just the PSU).

One more thing: when you starts the PSU with the 1kohm resistor than it should be enough just a short connection and release. Check the multimeter. If you connect the PS_ON to GND and the 12V appears than release the jumpstar resistor. Two things could happened: 1. 12V dissapears than the connection should be keep during the power on time. 2. 12V stays. In this case the next short will switch off the PSU. It depends on which standard HP is implemented.

@mimihaly This was extremely helpful actually. This is one of those issues I have been overthinking. My grounds match with what you found. On the board side, I will have to take the board out again and measure voltage. Although it does make sense that there is still some level of power on pin. Despite the fact that the PSU does get some kind of power when disconnected from the board (12V rails on the 12 pin are present)

I am not getting anything on any of the pins on the 18 pin however.

Can you get me resistance mode or diode mode readings for the rest of the 18 pin connector connector on the board side? Just to compare?

OK, for further reference I suggest to name the 18 pin connector to C18, the 12 pin connector to C12.

My diode mode measurements:

on C18:

MM ground probe on GND, positive probe on test pins:

P1: 1.255v

P2: capacitor charging

P3: capacitor charging

P6: capacitor charging

P7:capacitor charging

P9: slow charging

P10: 0L, reversed probes: 0L, possible output?

P11:capacitor charging

P12: 0L, reversed probes 0.751V possible output?

P13: capacitor charging

P14: capacitor charging

P18: capacitor charging

Pins not mentioned are GNDs.

on C12:

MM ground probe on GND, positive probe on test pins:

P1: capacitor charging

P2: capacitor charging

P3: capacitor charging

P4: capacitor charging

P5: capacitor charging

P6: capacitor charging

P8: capacitor charging

Capacitor charging means the measurement starts with 0.5V and quickly - 5-10s - rise to 2.9V and it changes to 0L. If you want to measure a given pin again discharge the pin first otherwise it will be 0L.

Before the measurement I recommend to short these pins to GND with a wire to discharge the input capacitors for one or two seconds. If you measure 0L on a pin reverse the probes and measure. Reverse back the probes and measure again. (its a kind of discharge).

If you measure shorts - continuous beep - on these pins than you have a problem: that rail is shorted but do ot worry most of the case it is easy to repair. But first the PSU should be in working order.

You measure no output voltage on any pin on C18 connected to Power and unconnected from MB?

You got 12V on C12 pins? If yes which ones? This is a bit strange because mem and cpu power should be present after the psu is switched on by the user but maybe I am wrong.

I suggest to deal with C18 only first. If there is no voltage on the pins when not connected to the MB than connect to the MB. Connect C12 as well.

Measure voltages on the C18 connector in the plugged state. Push the multimeter measure probes to the top of the connector, you should reach the connector's pin with the probes - you should see the top end of the metal pin in the connector-. In case of the ATX PSU it is possible to measure this way with plugged in connector.

Than push the power on button on the front panel and measure again the C18 connector.

Please reply back with the measurements.

Waiting for your results.

I am not sure if the ATX converter cable is applicable for the Z4G4. According to the sticker on the PSU several 12V and one 5VSTB is provided on the C18, and several 12V rail on the C12. There is no 3.3V rail in the HP PSU. There is not exact pinout of the two PSU connectors therefore the ATX PSU connector conversion can not be determined yet. Please note you face one more problem. There is no pinout for the front I/O connector as well, therefore the switch on-off button pins should be determined by experience on the yellow male pin header. In order to start the PSU and have right signaling on the chipset this is a must I believe. I am in the same shoes as you. Still looking for somebody have a working system an be able to measure the C18, C12 by multimeter to document the pinout of these connectors.

@mimihaly Agreed that is does not match the standard 18 + 12 pin that was previously posted.

@marcoguerra I have read in places that it is unwise to use adapters like this for this specific PSU for numerous reasons. It may be able to be done, but there would have to be some rewiring at a minimum to match the pinouts on this power supply and I would question that it would be worth it rather than buying an HP power supply.The risk for damage to the board is too great in my opinion

Alisha, based on your measurements on C18 it seems the PSU provides all the main (5V, 12V) rails on that connector. PWR_ON switching is working as well.

Pin 12 needs to be investigated. It is definitely driven by the MB. The measured 1V is not normal I think. Measure it on the PSU's connector without connecting to the MB please.

The 3.3V pins (Pin1, Pin 10) should measured C18 disconnected from MB on the PSU side.

Pin 2 measurement is a promising one. On standby it is 3.3V, switched on it is GND. It indicated that the given rail is shorted to ground when the PSU is switched on. Let me check on my board which power rail belongs to P2. If you are lucky only a shorted mosfet is your problem.

@mimihaly I checked any of the mosfets I could spot readily for shorts (and voltage) and checked coils for appropriate voltage on both sides and found everything as I would expect. Doesn't mean I didn't find th problem, but I would be very okay with that if I am nust missing something.

I have a new power supply coming tomorrow just to rule it out, but I would be very okay with a shorted mosfet. I'll keep you updated.

Alisha, is it possible to PM you? If the existing PSU turns to be bad than I am interested to buy it if it is for sale.

Regarding the board: something pulling down the P2 from 3.3V to GND on switch on. I measured P2 as a power input on the MB.

I would check it in the following way: using a variable power supply I set the current limit to 3A and I powered P2 only starting from 0.5V and increasing slowly up until it reaches the 3A limit or 3.3V. (voltage injection) If you reach 3A before the 3.3V (very likely) than check the MB what is getting hot. Use infra camera or isopropyl alcohol to identify the component getting hot. Possibly a shorted capacitor but who knows.