Agilent Infiniium 54853A DSO won't power on

[simmconn]

The model number of the motherboard is VP22 in my units. The user manual is attached.

I noticed that you have not reported the +5VSB voltage under the load, only the current numbers. So I can't tell if you have the exact same case as mine, though very close. The standard ATX supply should be able to supply 500mA to 2A (depending on ATX spec versions) while maintaining voltage within ±5% of 5V. I don't have a new unit to tell if a 'good' agilent PSU is within the ATX spec or not.

What I observed on my unit is that when the loading is at ~200mA, the +5VSB output voltage is below spec (about 4.7V).  Although the PSU shouldn't go out of regulation under that loading, a healthy motherboard shouldn't draw that much current, either. I have two choices, either fix the PSU such that the +5VSB does not drop that much under load, or fix the motherboard such that it does not draw that much current, as a result the +5VSB will stay within spec. I took the latter approach. The fix was as simple as running a wire on the motherboard. 

I made the fix for my own units and didn't document the details for public consumption. But all is done with careful measurement, analysis and calculations. If you decide to try my approach, PM me for the details.

[cncjerry]

This looks exactly like the typical ATX motherboard power on problem.  Typically there is a bad cap in that circuit.  I have an HP computer with this exact same failure and after an extended power outage I bring it up by shorting the green wire to a black (ground) and after it powers up it will usually power on with the soft button.  You should check the caps on the motherboard in the APM circuitry if you can find it.  Look on the web for ATX power on failures.

[russeree]

Hi, just letting everyone know that I have the same issue with my Infiniium scope  2ch, 2gs/s 500mhz. Symptoms include after being disconnected from mains the scope fails  to start back up upon pressing the soft power on button on the front of the scope and a power supply hum.

Sightings Include:
Once scope has successfully powered on the voltage across pins 3 and 11 will stabilize at 2.77 volts when loaded with a 180ohm resistor.
Below I have posted the wave output across an 180 ohm resistor when the scope PSU is humming and the scope has not entered a power on state.
The voltage at pin 11 measures 15 volts with no load. This leads me to believe this is the PS inhibit signal.
The voltage at pin 3 measure .22 volts with no load.
If I place a external power supply ground on pin 3 and 5v on pin 11 the scope boots with no problem (external ps current draw is 18mA) Anything above 6 shuts the scope down and below 4 wont power on.
Once the scope powers on all rails are perfectly in spec. The issue is intermittent power on.

Any help would be appreciated.

Pin 11 is the inhibit line.

[Jwalling]

Hi, just letting everyone know that I have the same issue with my Infiniium scope  2ch, 2gs/s 500mhz. Symptoms include after being disconnected from mains the scope fails  to start back up upon pressing the soft power on button on the front of the scope and a power supply hum.

Are you sure you're in the right thread? The 54850A series did not have a 500MHz version.
You might have a 54820A? I'm not sure that they even shared the same power supplies. The service manuals should be checked.

[Samogon]

I have also hp 54845a and it also fails cold start after AC line is disconnected. But if it sits for a few minutes wit AC connected it can start with soft power button no problem. I suspect high capacity electrolytics in PSU to be old, going to replace them. All power rails are at specs when unit is powered on. When off, inhibitor voltage is normal too, also can start it by connecting 200Ohm resistor to power sense pins 3 and 11 on the PSU control connector.

[INFINIUM]

I try this trik  200   ohms to start the P. Supply in my  hp54845  , NOTHING  ,  it seems that the PS is damaged ,
somebody knows how to start it  in another way , I am looking for the schematics also. or replace it for a new PC Model.

[INFINIUM]

power supply connector pin assignment .
I am looking for this for a new PS.
There are 20 pins more the vertical conector inhibit signals or
In the bottom connector maybe is  5 volts +  ,, minus   , ground is the screw holes .
the other conector is more confused

 in pins  1-2 there is  a condenser , voltage 

pins  3-4   and 5  another condensor   3-4 is positive voltage ??
 6-7  positive   condenser negative to  9-10    voltage ?
in total  in this conector   3 voltages  maybe the  +  minus  12 volts  and another one?
if somebody can check those voltages with an alive Power supply  , is very confusing 
I wanted to put a new PC power suppy    I need the original power supply connector pin assignment

[INFINIUM]

The only schematics  looks easy.

[INFINIUM]

LIN SINC   from power supply to  OSD .
Is not so easy  I want to replace the death original power supply for another standar .

[INFINIUM]

The  ATX-PIN out   is here  , of course is not the HP 54845a   
if I made a mistake 
i need more time to transplant this new PS  to the old connectors ,

[INFINIUM]

From one company selling the PS   I  see in the photo that the blue condensers in the middle module the brown one in the bottom right  and the big transformer with blue cables is different from my PS or they changed it when repair..

[INFINIUM]

https://en.wikipedia.org/wiki/Failure_of_electronic_components

I guess here explain in general the problems I have ... the time is killing evething slowly