PowerBook 100 & black screen

[bbraun]

I've got a pb100 with a screen that comes on, the backlight comes on, and it looks like all the pixels come on and stay black. Brightness and contrast knobs do not seem to affect anything. After power on, it chimes and attempts to access the (dead) hdd.

I started with the usual, leave it on and see if the LCD comes on, use a heat gun, etc, no changes in behavior were observed. So, since these are all old caps that probably need replacing anyway, I've recapped most of logic board (I haven't touched any of the 1uF's, 3 radial 100uF's, and a single 4.7uF, I need to order replacements), including C22 which apparently is known to cause problems with the lcd bias voltage.

So, I've opened up the LCD, and there are 2 electrolytic caps on the board in the picture. C4 seems to be 47uF 16V radial, and C1's (near the connector on the left) label is obscured by other components, I'll need to remove it to read the label. But there are tight height requirements for the caps, and the 47uF replacement I picked up from RadioShack is too tall. I was wondering if anyone else has replaced these, and has a good source for them.

Or, if this is a known issue and I'm being dumb, that'd be good to know too.

[techknight]

This is an odd one. Usually when you have bad capacitors in the panel itself, you get some sort of an image. just not a very good one.

Hey for shits and giggles, take the LCD panel out of the metal frame. (disassemble panel). Check for leaking caps there, but more importantly check the picofuse(s) on the panel, as missing logic voltage will cause the same thing, your BIAS voltage is present but your logic voltage is not.... ive never opened, seen, or owned a PB100, only the newer models and they are different.

[tomlee59]

I started with the usual, leave it on and see if the LCD comes on, use a heat gun, etc, no changes in behavior were observed. So, since these are all old caps that probably need replacing anyway, I've recapped most of logic board (I haven't touched any of the 1uF's, 3 radial 100uF's, and a single 4.7uF, I need to order replacements), including C22 which...{snip} is known to cause problems with the lcd bias voltage.

Try measuring the voltage across the cap to see if you are getting the -21V bias. You should see this voltage at one of the connector pins as well. If you don't see it, that's your problem, and C22 is a likely culprit.

I recall DigiKey having suitable replacements. But before bothering to hunt down parts, just make a couple of measurements to see if that's even necessary. And also be sure to perform the standard "pull out the flex cable, reinsert the flex cable" ritual a couple of times to see if that fixes anything.

Good luck!

[JAG]

I have the EXACT same problem on my PB100.

Got it off Craigslist a year ago and fired it up no problem. Took it out again a month or so later and black screen.

I can hear the drive spin up (which it wouldn't do when I first got it until I gave it a few good whacks)

I'm reluctant to start taking things apart without having a more targeted approach to fixing it.

Please post back with any results!

[bbraun]

Try measuring the voltage across the cap to see if you are getting the -21V bias. You should see this voltage at one of the connector pins as well. If you don't see it, that's your problem, and C22 is a likely culprit.

Thanks tomlee59! Sorry for the late response.
Measuring the voltage across C22, I don't get -21V, In fact I seem to get almost nothing (-0.23V). I also don't see -21V on any of the LCD connector pins. I've already replaced C22, that's one of the first I replaced. Any hints on what's feeding C22? There are two opposing 220uF capacitors, C23 has about 12V and the one next to it is about 5V, those have been replaced as well. There are three 100uF ones near those that I haven't replaced yet. I'll check those out, I guess.

[techknight]

check SMD Picofuses on the panel and on the motherboard, if the cap went bad, its possible it kicked out a fuse.

[superpantoufle]

I'm very interested in this topic, since my PowerBook 100 suffers the exact same issue. I've talked about that PowerBook in this thread about my website (still under construction) pomme-s.ch which is (actually was) served up my the 100.

That PowerBook had been up and running 24/7 from february to november, without an issue, online and serving up the website. I had to reboot it twice after a crash. Then about two weeks ago I shut it down to move it and take some pics for the site. And boom, no way to turn it back on. Well, it boots just fine (chime, spinning hard disk and system booting), with no display. Just as you describes it, the backlighting is on but all pixels stay black.

I haven't recapped anything yet, but I did switch displays with a dead 100 I had around for the parts, and the exact same result. So I guess the issue is on the logic board rather than on the LCD?

I was thinking the issue may be related somehow to power, since my PowerBook wouldn't have enough juice to boot on its original power adapter. It would light the screen, but couldn't get a chime nor anything. It was just fine with the beefier 1xx adapter.

Now the website is runned by a 145, as the 100 is waiting for a fix...

[bbraun]

I've replaced the three 100uF caps I mentioned, no change.
I'm not entirely sure about the picofuses, but I don't see anything...
I'm still concerned about what tomlee59 said, I should have -21V across C22 and on at least one pin of the connector to the LCD, but I'm not seeing -21V anywhere even after replacing it.

[techknight]

Well if the boost inverter that provides the voltage isnt running, thats why. I dont have a PB100 in front of me, but i know on quite a few powerbooks there are pico fuses around the board. and one of them blown in the boost inverter circuit would cause it. You could also have a shorted transistor instead as well. Time to find out where the boost inverter circuit is, and check it out.

Then again, Im not sure.

[bbraun]

There's a couple fuses on the top of the board, and a bunch (maybe 2 dozen) on the back of the main logic board. They all test out continuity wise.
I don't know about that -21V, but I do know the power to the backlight is good, it packs a jolt if you touch it.

[techknight]

Well When i refer to the "boost inverter" I am referring to the circuit that takes the 7.5V DC input and converts it to the -21v.

Measure the resistance across the capacitor to make sure the circuit isnt shorted.

If not, and you feeling "frisky" Create your own -21v supply (isolated ground btw) and supply the bias

Dangerous i know, but hey. worth a shot?

[tomlee59]

A floating supply isn't necessary if you have a negative-output supply -- just connect the external PS ground to the PB's ground, and you'll be fine. Or rig up a few batteries (say, a couple of 9V batteries and a couple of AA cells, say).

If adding the substitute supply causes an image to be displayed (you may see a somewhat "ripply" display; don't worry about that -- all we care about at this point is an image of some kind), then the -21V panel bias is your problem for sure. Measure the current being supplied. If it's significantly greater than about 10-20mA, your display is excessively loading the boost inverter, causing it to go into current limiting. If the current is low, your boost inverter is simply dead.

I recall tracing part of the inverter, and there's very little there. There's one impossible-to-find chip, and a handful of discretes. All I can say is, hope that the problem isn't the chip, because you will have a tough time finding a replacement (other than scavenging one from another PB100).

[techknight]

build a 555 timer replacement circuit. ROFL.

[nvdeynde]

I fixed my Powerbook 100 by replacing all capacitors on the logic board and in the LCD panel.
If you take an ESR meter, you will see they are all faulty and most of the leaking fluid badly.

Also make sure the battery switch at the back of the powerbook is in the upside position.

If you open the powerbook 100 for repair, it's also best to remove the metal lever from the battery sensor switch which sits just between the 2 battery terminals on the logic board. Just remove the metal clip from the switch: this will prevent that the powerbook tries to charge or take power the battery and has another advantage that you can keep the Pram settings when you insert 3x CR2430 batteries.

If you don't remove the metal clip from the switch: the powerbook 100 will always loose his Pram settings when you disconnect the power adapter, even with brand new CR2430 batteries installed as it assumes it still has power from the main battery.

Nico