OptiPlex 780 no boot up etc

Question

My OptiPlex 780 is not booting up and failing POST.This problem actually began a few months ago but as I mention below I was able to work round it until now!

When powered off a regular pulse continued to sound across the speakers.When attempting to power up I found the power switch was completely dead.However the PC would power up via the test button usually first time,but occasionally only after repeated attempts.In order to overcome this I simply kept it powered up all the time,restarting periodically and this was fine.Unfortunately I live in a rural area where intermittent power cuts are not uncommon.Using the above fix got me back up and running until now.The current status is as follows:

1.Power switch remains unresponsive.

2.On power up via test-button machine fails pre-POST.

3 Solid amber light and flashing LED 3 4

The Dell service manual diagnostic suggests power supply is OK and a memory failure.I have tried power up with all external devices removed and by removing each of the 2 memory modules in turn and also by swapping them around and trying them in the various slots etc-all to no avail.

I have very limited financial resources and urgently require my PC to be functional ASAP.

Will purchasing a couple of new memory modules be enough to resolve the issue,even if temporarily,or is the problem more complex?All help gratefully received!

fireberd · Answer

This is a 9 year old PC. Most anything can be wrong, and I doubt new memory will fix it. Old style memory is relatively expensive.

Based on your report problem is more likely motherboard related. However, one thing inexpensive to try is the CR2032 coin cell battery located on the motherboard. This is for the CMOS Memory (BIOS) and can affect power on self test (POST) and cause errors.

Nocab · Answer

Replaced CMOS battery with one I know to be sound-now getting flashing amber IO light as soon as PC is connected to power supply and then on start up(via test button)goes to solid amber with no flashing LED!This speaks to me of power supply problem-could this account for the previous symptoms?Or is it as you say,more likely to be motherboard related?

speedstep · Answer

Blinking Amber power button is bad powersupply.

Solid Amber power button is motherboard dead.

Replacing power supply MAY help but at this point of keeping a unit running with bad power supply you may have fried the CPU and everything else.

740 755 760 780's are not expensive. You can get a new TOWER for $100 or less.

https://www.lambroinc.com/desktops?lightbox=dataItem-jtfsw8uq

Non Tower units are NOT recommended due to the tiny power supply size.

Tower units require ADAPTER for standard power supply from MODDIY.

https://www.moddiy.com/products/Dell-980-960-780-760-PSU-24-Pin-to-Mini-24-Pin-Adapter-Cable-10cm.html

Diagnostic LEDs for the OptiPlex series (2005 to 2009)

https://www.dell.com/support/article/us/en/04/sln284978/a-reference-guide-to-the-dell-optiplex-diagnostic-indicators?lang=en

Off	Blinking Amber	Solid Amber	Solid Green	Blinking Green
The computer does not appear to get power from the Power Source.	The PSU is receiving power from the Source, but is unable to distribute it.	The PSU is working, but the system doesn't process data. BAD MOTHERBOARD OR CPU	The system processes data and has begun POST tests. (See the diagnostic LEDs at this point)	The system is in a hibernate or sleep state.

savvy2 · Answer

I've answered this vast times now.

Do the HARD POWER RESET YET? this is FIRST THINGS FIRST THING. (power surges HAPPEN)

well I guess you are saying the power button is dead?, and fans dead silent too. 100% dead.

there are 2 causes, (that expand to tests) we can only do 2 things, guess or test.

1: PSU BAD. (swap it out)

2: PSU is overloaded ( sees one). ( we do the strip down test to prove that and if still fails , a new PSU solves the problem.) overloads are a.k.a as short circuits, even lightening damaged devices HAPPEN.

that button trick, means what>? lets go there...

that BIST button you push, this bypasses the intel south bridge chip (power controls inside) and forces the PSU to turn on the Illegal way (but safe) the South bridge is confused, or sees overloads. (etc)

the south bridge , needs standby power to work (i use a voltmeter to test that) and also not locked up in sleep mode.

do the hard reset first. ok? this cures like 90% (if PSU not DEAD ) (PSU have many failure modes not just dead) (if your SW drivers are bad, and sleep keeps locking up, this is only band-aid, the reset)

the PSU can in fact not turn on if it sees overloads, the ATX spec on that is 1 second or less. or is informed about overloads. ( one way is called OCP , over current protections)

my modern PSU (DSP fancy) does it in 16mS .016 seconds. faster than you can see. T = 1 /F math.

the PSU can be bad

the PSU can see shorts (and more, up to 5 way power protections are in top PSU brands)

the MOBO south bridge and all VRM on the mobo can tell the PSU , I am overloaded. and do not run.

all in the wonderful ploy to stop fires. ( gee golly wow)

no money.. "what will be will be..." money does not rule fate , ok. things can actually fail and short out.

A PSU can be had used off fleabay most times for a whooping $15. ever look first?

if I had 1 PC, id have a spare PSU, sure would.

short answer?

if the hard reset fails and the strip down test fails, the PSU is bad, 99% (rare would be mobo bad. and silly expensive guess to try swap it first)

that PC is old 2009 PC , 1 decade old, most this old have bad, coin cell, bad HDD and now a bad PSU.

most this old ran for 10 year, constant or heavy the CAPS in the PSU dry out and go bad. EOL, PSU.

there are some stats.

every thing has live span... some are short, others are up to 100 years in any PC.

a good tech, knows what lasts and not. (tells him/her what to check first)

Nocab · Answer

Fan runs-but boot up stops pre-POST-I tried hard start,removing all devices,memory module reduction/swapping,changing CMOS battery etc. etc.

Conclusion? Yes all things have a lifespan and this one is well and truly spanned!Problem being that I am reliant/addicted to having a functioning PC and I am without the funds to replace it-and will be for the foreseeable future! Ah well-they say what doesn't kill you makes you stronger!

Thanks for your input though,and the other kind folk who responded to my pleas!

Optiplex Desktops

OptiPlex 780 no boot up etc

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