Thursday, May 19, 2011

Toshiba A75 - No picture on screen.

TOSHIBA A75 series are workhorses they will run and run.  The only problems I have experienced with this model  that is fairly common is the DC Jack fails, Overheating and onboard memory failure.

Since onboard memory can cause the above symptom, that was on of the first things I tested. The memory turns out to be fine. Opening the unit I see that there had been a previous spill that had dried and and was on some important VLSI chips. The next step was to closely inspect the spots where the spill was and visually determine if it could be the cause of failure.  This depends on whether it was on any PCI or video subsystems.  As it turns out it was on the PCI subsystem.

Tuesday, May 10, 2011

Explanation of Terms

Some of the terms used by techs and myself:

Means No Power, No Lights, No Charge Light.

  Check DC Jack, test with known good battery

No Power/No Lights:
The unit will work from charged battery, but not from AC. Some light may be on.

  Check DC Jack.
When you move the charge plug with battery installed, the charge light may come on intermittently. This is caused by a cold solder joint on the DC Jack, or bad contact inside the jack. 

No Power/With Lights:
If you hold the plug at an angle, the unit will come on, but letting go of plug it shuts down.
  Check DC Jack

Will Not Charge Battery:
Unit runs when plugged in, but will not charge battery. Or the battery only last 15min after charging all day.
   Check Adapter - Generic or Wrong Amperage
Example -If you are using a 65w charger and trying to charge a DV9000 the battery will never fill up to it's maximum.
Volts x Amps = Watts   18.5v x 3.47a = 64w  and  18.5v  x 4.47a = 90w

Posts and starts to run, then reboots.
   Suspect CMOS battery
   BIOS settings.

Lights Flash:
Lights on panel flash when I press the power button:
   Suspect dead/near dead battery.
      Check DC Jack
      Check Charge Adapter

Blue Screen of Death [BSOD]
Very common issue with hardware changes or failure, wrong drivers
   Start laptop, continue to press F8 until you get a Start Up Menu
      Disable Auto Restart 
         Restart in Safe Mode - Disable all items in Startup until you take to shop
            Or uncheck all unknown/unverified software
You can also remove or disable unused items in System Hardware, modem, network cards and reboot until culprit is found.
Those are just some of the symptoms that you may read on this site.

Some questions that were asked.

A few individuals have asked questions direct, and I wish to clarify some items.  It is best when you post on the blog that way it can also answer several hundred other readers questions.

Question  1: 
How do you check the (brown) ceramic caps.
Simple, I use a standard Ohm meter in the Resistance mode.  Since the biggest problems with caps when they fail is the become either a direct short, or they will never store capacitance (open).  The meter reads in the ohm mode by sending a small amount of electricity through resistors and report the difference in Ohms. Test with leads RED on one side and Black on the other.  One direction will give you a high resistance ~2000Ω and then reverse the leads on the meter and the other direction should give you Infinity. This is an OK capacitor. If you have a very low resistance or 0 (zero) Ohms, the cap is shorted.

Why?:  I started small just repairing for friends and family, after a number of common repairs I saw the need for a shop, so when I opened the shop I was looking at the prices of equipment (oscilloscopes, digital probes, professional hot air guns, and all the high tech test hardware) and the prices were too high for the amount of work I was doing. So as I grew, I got comfortable with what I had, and never changed.  If it works why change it?.  The success rate would could not be improved enough to justify the high dollar purchases.

Question 2: What are the soldering tools you use.Answer:  Ordinary hobby tools for the most part.  The soldering pencil is a 40w medium tip Weller type with base.

Then there is a soldering station that was purchased from Radio Shack with a small pencil tip, for the very small parts.
The key to a good solder joint is heat management, and flux.  When you are soldering large items, you should have a larger tip. Flux also assists in distributing heat as well as removing oxidation from the solder pads.  

The desoldering iron is a simple Radio Shack that cost about $12. Though it should be cleaned often, unplugged when not used. (the tips don't last long)

A scope would be nice (any donations?)  just kidding.

Other Tools do include a combination Hot Air and Soldering station (collecting dust) I just use it when I get into tight situations or the need for speed or controlled heat arises.

Monday, May 9, 2011

DV9000- Turns on- Shuts off

Symptom 1:  Unit runs for a while then turns off
Symptom 2:  Unit turns on, turns off immediately

This unit arrives after another tech had attempted repairs.  Numerous screws missing from base and incorrect screws used in reassembly.  Complete tear-down and disassembly.

After powering the unit up, I noticed that the heat sink copper was discolored [darkened] which is a sign of high heat.  Upon close inspection I noticed a kink in the heatshrink material covering the wires for the fan wires, so I strip back a portion of the insulation and the red wire was broken, and the black wire was only 2 strands. Yellow and White wires were OK.  Rather than replacing the fan (which is in short supply, and costly) I repaired the broken wires with solder and insulating them so that they would not short each other or the frame of the HS fan, which is negative ground.

Screw also missing on the exterior frame that holds the heatsink downward onto the base, this screw is important because it also keeps the heatsink pressed against the GPU allowing for the heat to be pulled away from the chip to be vented out from the unit.  This unit was also upgraded to the modified custom copper shim to further assist in heat reduction.

Reason of varying symptoms:
This model may not require the fan to reply back to P.O.S.T. -so it would run, until it got too hot to continue. The ground (fans black wire) did not complete the circuit for the 'non-working' temp sensor to report that it was overheating.  The CPU core thermal sensor eventually reported overheating before the fan could, or CPU thermal sensor would shut it down to protect the CPU. Then when the unit was immediately turn back on (while still over temp) it would shut off, since no correction was made, the info was reported to CMOS and would shut off.

This test should also be in your diagnostic 'toolkit' so that you also test the fans when you have an immediate shutdown, or runs & shutdown problems in this series [DV6000/9000/F700].  Also see the specs on MAX8734 power chip so you can identify this cause, since it do have a SHUTDOWN circuit [pin 6].  

Cause: The screw had gone through the base and was smashing/pressing the wires again metal post, effecting shorting positive terminal of Fan lead coming from motherboard connector,  and broken, no power reached the fan.  The black wire [GND] was nearly broken so the fan circuit was not complete, as well as the speed (YEL) and temp sensor (WHI) circuit because there was no power reaching the fan.

The Max8734 is one of the major players in distributing voltages to sections of the motherboard. 

MAX8734AEEI+ product name
High-Efficiency, Quad-Output, Main Power-Supply Controllers for Notebook Computers