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Toshiba T1900C

One last thing. Did you have the power supply plugged in? If so, remove it, and try again.

first no psu, while I gave 12V to the battery leads on the mobo.
I did try also giving both, 19V psu (to the pwr connector) and 12V to battery leads, but that changed nothing either.

I did notice now that that 3V lithium battery what was earlier removed, is rechargeable.
That may be why it still had 3V voltage - a couple of days ago I did have the psu connected over night.

Still wondering, what is the purpose of that second dead, small finger battery.
 
It might be the RTC battery. If so, it needs this to post.

batt.jpg

I found out from t1900c maintenance manual about the batteries. RTC battery is in fact that rechargeable 3V lithium battery.
I connected it and tried to boot -> still no change.

Next, I was thinking to make the printer port led tester. It would not be very difficult to make, but I also noticed, that
there are bios configuration requirements for it to work, thus it maybe not helpful after all.

pport.jpg
 
Just found out information that there is a 5amp fuse on the lower system board and 2 amp fuse(s) on the higher system board.
I have not checked these, since I was not aware of them before, but they go on the check list now.
 
Go ahead and check the fuses, always a good check.

In your 4th photo showing the power supply there's two light blue electrolytic cap's and both have bulged tops, a sure sign that they need replacing. Others ???

Check the RTC/BIOS battery for 3vdc to see if it is still okay - with main power removed. Then test again with power plugged in to see if there's voltage higher then 3vdc charging the battery. I doubt if a bad battery would prevent a boot, but while in there testing that's a test of the poweer supply to see if there's any voltages coming out of it (them).

Also check for voltage going to the on/off switch since it needs to have power at all times so that the laptop can be turned on. On newer stuff it's often 3vdc, but on older laptops it might be 5vdc or GOK's. But one pin needs to have voltage and time there's the main battery or AC adapter power so pushing the button starts the boot process.
 
Thanks DeltaDon for your input!

I did remove the two light blue caps. My eyesight is so bad that I can't really see if they are bulged or not, but
others on the internet reported that these two were bad on same model laptop. I'm also starting to think that I need to
start putting back some caps where I have removed suspect ones. And then checking if there is any change.

I will check RTC voltage, when psu is connected to the mainboard. First thing on monday evening, since I'm out of home for the weekend.

I kind of believe, that on/off switch is working. When I connect psu to the motherboard, DC IN led stays on, green.
It does not blink. Only when I press on/off switch, the DC IN blinking will start (one long, three short blinks).
But, I can still check the voltage for that switch too.
 
I did remove the two light blue caps. My eyesight is so bad that I can't really see if they are bulged or not...
Visual inspection will not reveal 75% of the issues associated with bad caps. IOW, for every bulging cap there are likely three more that do not show any visual signs of being defective.
 
Wait... You tried powering it up with missing capacitors?

No wonder it doesn't work right. They're needed to complete some circuits.

ahm, a bit shamed to say that that's right.
I once had shorted tantalum cap in 1541 drive and removing it enabled the drive to boot.
But, as said in this thread earlier, only tantalums get shorted and that test cannot apply here.

So, my search for spares starts here.
 
Electrolytic capacitors can fail short as well, usually caused by short but extreme power surges.

I have a biostar board with caps that look fine, but have completely failed short around the CPU.
 
I'm fighting a failed S-100 system at the moment just because a single electrolytic capacitor in the power supply had one of it's leads break free from the circuit board. The net result was that the diode bridge output of pulsing DC took out the voltage regulator and the 5vdc output went to 24vdc and smoked the floppy drives and other circuits.

You need to put new main regulator cap's in NOW and hope you haven't done more damage to the Toshiba. Removing a single bypass cap (like your tantalum) is not the same as pulling the main cap's in the power supply. For quite a few years a large number of TV's and other electronic devices were FUBAR just because the cap's in the power supply failed to regulate the output power. Replacing the cap's often returned the equipment back into operation. They can not be left out.
 
That's hard to believe, unless the cap played some other part than a simple filter cap. I have no doubt that the 120Hz unfiltered PSU output made the system act up, but I can't see how it would blow out a voltage regulator or floppy drive.
 
Any update for this?

When all the caps are desoldered, clean the board off with isopropyl alcohol to remove any electrolytic fluid that may have leaked from failing capacitors.
 
That's hard to believe, unless the cap played some other part than a simple filter cap. I have no doubt that the 120Hz unfiltered PSU output made the system act up, but I can't see how it would blow out a voltage regulator or floppy drive.


But I don't wish to steal this thread, just commenting that things go FUBAR when main filter caps aren't installed. However, pwr. supply designer cheaped out, IMHO, and used one winding output transformer to supply +24 and +5 v circuits. Also no solid mechanical mount for the main filter cap. Main filter cap lifted free from the board. The +5vdc circuit using a 723 IC with 2N3055 driver trans went to full unregulated ~30volt and believe me the magic smoke came out of the floppy drive.
 
Any update for this?

When all the caps are desoldered, clean the board off with isopropyl alcohol to remove any electrolytic fluid that may have leaked from failing capacitors.


Thanks for asking, DankEngihn!

I got back home today and wanted to check this again.
I found five fuses, that were all ok. Which is kind of bummer, it would have been
easier fix (but of course, if fuses were busted, something else probably would have been too...).

I pulled suitable caps from old atx psu. Replaced the 1000uF cap and the two blue 220uF caps
from used spares, since I got no new ones to try with. I then tried to boot, but the DC IN led blinking
was the same as before.

I measured RTC battery, it was now 2,91V when no charging and 3,25V while charging.
The power button has 4,77V on one leg (when pressed down zero volts). I believe power button
is working as it should.

I got up 3am today and drove some 200 miles to my working town. It's now about 8pm
here and I think I need to continue this tomorrow. Fighting against fatigue while trying to fix
things might just make me mess things up more.


edit:
granted, that I may well have done some damage to the unit myself by trying it without these caps.
But I've been thinking about others who have fixed t1900c laptop with faulty capacitor(s).
They reported, that the machine actually turned on for second or two, and then immediately shut down.
This unit is just dead - apart from the DC IN led blinking.

This has made me think, that there may also be something else wrong with the unit and not the caps after all.
CPU ? rams ? I guess a number of things could go bad and make the unit just have black screen.
 
I'm suspecting that it's the power supply.

Try to get your hands on an OEM Toshiba 19v power supply.

EDIT: the picture you posted showing both of the boards looks odd. On the power board, between the"Toshiba" chip and the "flash" chip looks suspicious.
 
Last edited:
Good early morning!

10.jpg

I think that suspicious area between toshiba and flash chips was due to light reflection.
There is a black stamp there, I posted a better picture of that area.

About the power supply - if it was the cause, why would the 12V to the battery leads
give the exact same symptoms ? I did try the 12V again now that all caps are in place, but
there is no change.
 
Thank you DeltaDon for the links.
I don't exactly see the same symptoms. I see long - dot - dot - dot and then pause.
That is curious, it would make 8 hex.

even if it is long - dot - dot - dot - long - dot - dot - dot (to make 8 digits), 10001000 -> it would become 88 hex.
Am I thinking it the wrong way ? is it 00010001 binary -> 11hex ? or 01hex if it is only 4 digit code.

But I think there is long wait after every 4 digits, therefore it seems to me it is only 4 digit long code.

In the T1900C maintenance manual there is one 08h code:
08h HDC overrun (DRQ)

But I don't have HD installed. The code applies to HDD test program in the diagnostics disc, so it is not the right code here.

I'm thinking to buy better multimeter. Would this be useful/reliable to check ESR from electrolytic capacitors ?

https://www.ebay.com/itm/Digital-Mu...=2740569140718c10d95c10244715befe96b1acc5458c

Not a bad price for multimeter, if it allows me to check capacitor failures.
Drawback is to wait easily 6 to 8 weeks before it would arrive from order.
 
manual.jpg

Heh, when all else fails, replace the lower system board. if that fails, replace the upper one :).
If only it was that easy to come up with working replacements. The maintenance manual was obviously
meant for service technicians to make warranty repairs. They did not have to worry about replacing
capacitors or faulty chips on boards.
 
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