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Toshiba Laptop w/dark screen

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Thanks to both C1 and Paul878. That is what I was thinking. In the beginning it WAS an intermittent problem and by putting pressure on the lower edge of the screen in the area of the inverter I could make it come and go. But then it just went out and I haven't been able to get it to even flicker since. I really have been pulling out my hair (what there is left). Is there any chance that there is something in the BIOS that would tell the FL to light? There has to be a signal sent from somewhere. I'm just pulling at straws here. There is a used MB for sale on eBay for about $25 and I'm tossing that around too. I don't know how much I can do with troubleshooting the MB without taking the whole computer apart. It is pretty much covered up with stuff. I will try doing what you suggested though. What the heck, can't hurt at this point. Thanks again.

Ray
 
One more thing.

With the computer unplugged (and battery removed), using the multimeter (MM), do a resistance check on each wire going to the MB via the connector (presumably this is the inverter connection to the MB). (One MM lead is to MB ground and the other lead will be to one of the connector harness wires.) Compare the readings of wires of the working unit to the non-working unit. Inspect the MB solder joints and connector pins (for good contact in or with the connector) of any wires whose readings which differ between working and non-working units.

Addendum

Based on the time and effort youve put in, an extra $25 is no big deal to achieve a desirable functional notebook. However, that decision may more so depend on successfully being able to replace a MB (ie, can be lots of screws and stuff can even be broken in the process/attempt). If you decide to try to go the MB replacement route, then remove the supposed defective MB unit first, then make your decision to purchase.
 
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C1 said:
One more thing.

With the computer unplugged (and battery removed), using the multimeter (MM), do a resistance check on each wire going to the MB via the connector (presumably this is the inverter connection to the MB). (One MM lead is to MB ground and the other lead will be to one of the connector harness wires.) Compare the readings of wires of the working unit to the non-working unit. Inspect the MB solder joints and connector pins (for good contact in or with the connector) of any wires whose readings which differ between working and non-working units.
Click to expand...

I think I know what you are telling me but keep in mind that I have replaced the harness that goes from the MB to the inverter and also to the back of the screen. Would'nt that be sort of like what you are saying?

R
 
Not quite. The harness is not so much in question. What is being considered is : Which pin on the MB THRU the connector and harness is different or suspect? It is a standard electronic servicing technique/procedure used for diagnosis when no circuit schematic is available. If the circuit of one wire shows different (effectively from the MB side of the inverter to the MB, then this helps potentially isolate the problem to a particular pin on the MB. The strategy then is to inspect and ensure that the pin in the connector to the MB is making good contact and one also then examines the trace on the MB from the suspect pin to where it leads to on the MB.
 
Ok, I get it. I guess I am going to have to buy a better multimeter. I have a couple of cheapies and they aren't up to the type of testing you are talking about. I really appreciate you taking the time to try to help me here. Thanks,

Ray
 
C1 said:
One more thing.

With the computer unplugged (and battery removed), using the multimeter (MM), do a resistance check on each wire going to the MB via the connector (presumably this is the inverter connection to the MB). (One MM lead is to MB ground and the other lead will be to one of the connector harness wires.) Compare the readings of wires of the working unit to the non-working unit. Inspect the MB solder joints and connector pins (for good contact in or with the connector) of any wires whose readings which differ between working and non-working units.

Addendum

Based on the time and effort youve put in, an extra $25 is no big deal to achieve a desirable functional notebook. However, that decision may more so depend on successfully being able to replace a MB (ie, can be lots of screws and stuff can even be broken in the process/attempt). If you decide to try to go the MB replacement route, then remove the supposed defective MB unit first, then make your decision to purchase.
Click to expand...

Yeah, this is pretty much what I suggested in post #21, but not as well said. I don't think the OP ever got back to me on that point.

mfenn said:
Oh ok, I thought from your previous post that you were done buying new parts.

The signal to the inverter to power on is one of the pins connecting the system board to the inverter input. Since you have two identical machines now, you can probe the contact points and make note of the differences.

That will give you some clue as to where voltage needs to be applied to turn on the inverter. Then you could probably hack something up that keeps the light on by applying voltage to the correct pin on the inverter.
Click to expand...
 
mfenn said:
Yeah, this is pretty much what I suggested in post #21, but not as well said. I don't think the OP ever got back to me on that point.
Click to expand...

Hi to all who have contributed, I guess in the thread string things get mixed up. I tried to reply to whoever was replying to me in the order that I rec'd. them but who knows what happens in the cyberworld. Anyway, I have been reading all the posts and trying to do what has been suggested but the multimeter testing is not possible right now because I only have a cheapie Harbor Freight MM. I have always wanted a good reason to buy a better one so maybe this is it. I used to sell tools and I would drool over the Flukes but I can't justify the expense of one of them. So, if anybody wants to suggest a good inexpensive unit, let me know. I have also been watching eBay for pieces and parts and have made a couple of offers for parts units. Please do keep sending any other suggestions along. I truly appreciate all the help.

Ray
 
Oh ya, about the MM test (if you decide to do an ohm meter check), since the MM would technically be supplying voltage to the MB, it is possible that MB pins with traces leading to a chip could result in damaging the chip. (PS: I have certificates in electronics repair.)

If it were me, I wouldnt worry about it, but if you do resistance checks, start with the lowest ohm scale first. Voltages checks are safe so I would try that first.
 
C1 said:
Oh ya, about the MM test (if you decide to do an ohm meter check), since the MM would technically be supplying voltage to the MB, it is possible that MB pins with traces leading to a chip could result in damaging the chip. (PS: I have certificates in electronics repair.)

If it were me, I wouldnt worry about it, but if you do resistance checks, start with the lowest ohm scale first. Voltages checks are safe so I would try that first.
Click to expand...

Thanks C1, I am going to see what I can find in a MM tomorrow. I can't spend a ton of money but I want something that is better quality with better probes than what I have now. I was wondering, when I'm checking voltages, am I working with AC or DC? I know it's pretty low voltage so I was thinking it was DC. I think this is going to be a fun project and once I get through it I might like to see about doing some more laptop repairs. It's very interesting. My old eyes take it tough though. I might also have to buy an illuminated magnifier. Thanks again,

Ray
 
Start with DC then do an AC check, but remember doing AC requires that the system be energized. Technically when assessing AC type signals, an O scope is the correct tool as waveform shape, frequency (including frequency stability) as well as waveform height are typically of interest.
 
C1 said:
Start with DC then do an AC check, but remember doing AC requires that the system be energized. Technically when assessing AC type signals, an O scope is the correct tool as waveform shape, frequency (including frequency stability) as well as waveform height are typically of interest.
Click to expand...

Ok, you just starting talking Greek. I know what equipment you are talking about but the theory eludes me. At one time, many years ago, I understood some of it but I have lost it over the years. I used to play around with tube type radios. Anyway, I will get a MM and see what I can do. But I'm sure I will have to rely on you for help.

Ray
 
The PWM wave that use to control the inverter is way beyond the range of a DMM, so don't be surprise is you get no reading.
 
Hey you smart guys, I am looking into buying a DMM. There are thousands to choose from. Can you give me some input on what to look for? I'd like to keep the price down but get one that is good for all around usage. Thanks for your help.

Ray
 
I have a Fluke 87 that I brought and used for over 20 years and it still works like new. During those years I have made a lot of mistakes and done a lot of stupid things to it ()🙂. I don't know much about the budget DMM and can't give you any advices on that.
 
paul878 said:
I have a Fluke 87 that I brought and used for over 20 years and it still works like new. During those years I have made a lot of mistakes and done a lot of stupid things to it ()🙂. I don't know much about the budget DMM and can't give you any advices on that.
Click to expand...

Thanks, I was just looking at the top end of Harbor Freight's and I'm thinking of buying one.

R
 
I bought a MM from Harbor Freight and I am going to attempt to do some checking on the two machines. I only hope that I don't do damage to anything that wasn't already messed up. Pray for me.

R
 
Ok, I did some testing. I'm not sure what I figured out but it seems there is some difference on certain pins. I tested the connector that connects to the motherboard and runs to the inverter and the LCD screen. Most of the reading are pretty close but there is one pin that has no reading on the bad unit and has a reading of 2.9 millivolts on the good unit. At least I think the reading is in millivolts. It's an auto ranging MM and the screen says mv. Everything else seems to be very close. So, what should that mean? Bad board, or something related?
I'm thinking that I may be in over my head without someone looking over my shoulder.

Ray
 
2.9mv AC or DC (just wondering; 2.9mv showing on an MM's AC scale could be a big deal when viewed on a scope; eg, could easily show as a couple volt peak-peak signal).

On the bad MB, where does the trace from the pin lead to? Inspect that trace and any solder joints which use that trace.

Just for giggles, what happens to the 2.9mv on the good computer when you:

- Hook up an external monitor, then
- Toggle the good notebook's on board LCD off so that only the external monitor is being driven

If that voltage on the good computer goes to zero, you in all probability found your problem (ie, no drive signal to the inverter on the system that is defective).

Unless you can find a mechanical type problem such as a bad solder joint or bad physical connection, it most likely is going to be a component. The problem will be trying to take any analysis further without a schematic. After that, even if it is a component such as an IC chip, there would be issues with getting the particular part and un-soldering it without damaging the board and soldering in the new chip without damaging it (due to heating).

Again, a working MB for $25 would be a preferred approach (time, cost and project risk).
 
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Thank you so much for your time. The readings are all in DC as far as I can tell. At least that's what the mete screen told me. It does seem strange that there would be absolutely nothing reading from that one pin when there is 2.9 mv dc on the other unit. I am leaning toward the used mb if I can still get it. Luckily it was here locally in SoCal. I would just feel a lot easier if I could be certain that that is the problem.
Again, thanks to all for trying to help me. I think I was born too soon and should have tried to learn more over the years.
Ray
 
This question is off the original topic but I was just wondering something. You smart guys must have the answer. How can you tell what processor will work with what motherboard. If I end up scrapping my original laptop, it has a centrino processor. The one that works fine is a celeron. Would it be possible to swap the centrino into the celeron machine? Just pondering.

Ray
 
Correct me if I'm wrong, but it sounds like the two machines have identical motherboards. In that case, you should be able to swap the CPU over no problem as long as it's not soldered in.
 
mfenn said:
Correct me if I'm wrong, but it sounds like the two machines have identical motherboards. In that case, you should be able to swap the CPU over no problem as long as it's not soldered in.
Click to expand...

As far as I can tell, the two machines are indentical with the exception of my original (centrino) has a iLink connector and the celeron one doesn't. Other than that I can't see any difference with the exception of the model numbers.

R
 
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