• Updated 2023-07-12: Hello, Guest! Welcome back, and be sure to check out this follow-up post about our outage a week or so ago.

Request for information about the PowerBook 170 inverter board and LED upgrade

PB170

Well-known member
Hi everyone!
 
I have an old and classic PowerBook 170 that I'm still using (along some more recent equipment, perhaps I should add :) ). Unfortunately the screen backlight is on its last legs. Since I recently upgraded the storage to a Compact Flash-card (through the amazing PowerMonster II), an upgrade to an LED backlight is very tempting (especially since I, after some basic measurements, discovered that the backlight consumes nearly a third of the total power – much more than the physically moving hard drive). I am of course aware of the fundamental differences between the two technologies and that it's not simply a matter of switching the backlights. I would also like to preserve the machine's current functionality, i.e. allow the backlight to be controlled through software. I realize that this likely is a challenging to near impossible venture, but if it is possible (which it should be) I would very much like to give it a try. To even get close to achieving this, however, I am in need of much more background information than I currently have. So, my question is: does anyone here have any insight or knowledge about what would be required or some bits of information to help me out? Any kind of help or input would be truly appreciated.
 
Below is an excerpt from the Apple's document "Macintosh PowerBook 140 and Macintosh PowerBook 170 Developer" on the display and backlighting (page. 32):
 
The Macintosh PowerBook 170 computer uses an active matrix display that provides a high-quality presentation of alphanumeric and graphics information on a 217-mm x 140-mm active display area. The Macintosh PowerBook 140 computer uses an FSTN display. Both displays are supported by ondemand CCFL backlighting similar to that used on the Macintosh Portable; however, unlike in the Macintosh Portable, display backlighting is not adjusted through the portable CDev but is adjusted manually by the user.who simply slides a mechanical control (potentiometer) to adjust the amount of screen brightness. The Power Manager performs an A/D (analog-to-digital) measurement of the voltage output from the control and sends it to a software driver (called .Backlight). The software driver then tells the Power Manager to adjust its PWM signal. The Power Manager filters the signal to a DC level and sends it to the CCFL inverter to control power to the backlight.


 
In other words, the slider on front of the computer does not directly control the backlight, but instead sends its output to the Power Manager chip, which then adjusts the power to the CCFL. Consequently, the backlight can also be controlled through software (dimming at low battery power etc.). The CCFL connects to an inverter board (onto which the potentiometer that connects to the slider on the case is mounted), which in turn is connected to the machine's interconnect board.
 
Attached are two pictures (top and bottom) of the PowerBook 170 inverter board. The brown two-pin connector connects to the CCFL, and the white 10-pin connector to the interconnect board and the rest of the computer. From what I can tell, most of the inverter board, as expected, seems to be dedicated to power inversion/transformation for the CCFL. It is a little difficult for me to tell what connects to what, but there seem to be ten solder points within the area of the potentiometer (presumably not all for the potentiometer), of which at least two connect directly to the 10-pin connector (at pins 3 and :cool: .
 
This basically is where I am at the moment. 
 
To sum up, this is what I would like to do:
  • Install an LED backlight that uses the same power source as the current inverter board
  • Keep the full functionality of the brightness adjustment slider (i.e. control through software)
 
Some basic questions I have at this point are:
  • Does anyone know what goes in and out of the 10-pin connector?
  • Could an LED driver board be directly driven by the power supplied through the 10-pin connector?
  • Is there an LED strip available on the market that would be suitable in size for these old PowerBooks? (I haven't yet taken it out to measure it, but would guess its roughly 140 mm / 5.5 in long)
  • Can anyone figure out how the potentiometer could be isolated?
 
Again, if anyone here have any insight or knowledge about what would be required or some bits of information to help me out, any kind of help or input would be truly appreciated.
 
Thank you all in advance!
 
 
Ps. I have also posted this question in MacRumors' forums, here: http://forums.macrumors.com/showthread.php?p=20533964
IMG_7005_2.jpg

View attachment 5068

 

Macdrone

Well-known member
I won't try and derail you plan, but ccfl' are still readily available and easy to replace in these.

Just a suggestion as you will most likely want to recap the screen while your in there.

 

PB170

Well-known member
Thank you for your reply! Good to know. I actually have a few other PowerBooks I could use for a spare CCFL, but an LED backlight is very tempting, and would last longer. 

Apart from the backlight being very dim, the display still works fine, so I haven't thought of replacing any caps yet. I had the impression there are more of these on the passive-matrix displays and thus more of an issue on those. I'm more worried about the tunnelling problem (although the display doesn't show any signs of it yet) and was thinking if I could do anything to prevent that.

I won't try and derail you plan, but ccfl' are still readily available and easy to replace in these.

Just a suggestion as you will most likely want to recap the screen while your in there.
 

Macdrone

Well-known member
Tunneling is the screen failing and I have a 180 that does it bad but I have not tried replacing its caps yet. If I get this 160 going correctly I'll hit up the 180 and tell you if it helps. It was a high use since new 180 bought in Japan by a writer so that could add to the cap failure.

 

Paralel

Well-known member
We have proven that the caps have no impact on the tunneling. The tunneling is due to the seal of the LCD failing and moisture entering the display, which causes a parasitic capacitance that produces the effect seen. So far baking the LCDs that are contaminated helps somewhat. Its the best we've come up with to deal with this issue, its basically a problem with how they were made at the factory, an inherent defect.

 

PB170

Well-known member
While waiting for some more insightful information from you guys, I made some basic measurements of the inverter board and input connector pinout myself. In case this information might be useful to someone else, I'm posting it here. Likely, the pin assignment is as follows:
 
01 Ground
02 Ground
03 Brightness potentiometer out (0–5.15 V)
04 Brightness control from the Power Manager (0.22–5.00 V – probably PWM, but not sure)
05 Unused
06 Power in (7.5 V)
07 Power in (7.5 V)
08 Brightness potentiometer in (5.15 V)
09 Contrast potentiometer in (FSTN displays)
10 Contrast potentiometer out (FSTN displays)
 
The question is if the input voltage is enough to drive a modern LED board, as modern inverter board input voltages seem to be higher. As suggested in the thread at MacRumors, I'll send a mail to lcdparts.net to see if they have anything to suggest.
 
If any of you have any other suggestions, or could confirm or elaborate on the connector measurements (in particular the brightness control signal), it would be very helpful. 
 

techknight

Well-known member
hmmm... maybe a new source for tunnel vision replacements? it might be a chinese copy, but who cares? 

 
Top