Macintosh PowerBook 1400cs/166 - Power Issues?

[TheMightyMadman]

Hi everyone,

I'm in the process of trying to repair a Macintosh PowerBook 1400cs/166 for a friend of mine.
When I first got it, it just clicked when power was applied, the screen didn't do anything.
Since then I've replaced all of the SMD electrolytic capacitors on the mainboard, control switch board, and LCD board.
I've also rebuilt both of the PRAM battery packs (4 x VL2330s, 6V 100mAh).
I'm using an apparently working M4896 45W power supply (24Vdc at up to 1.87A).

All that happens is the power LED lights up solid green constantly, the machine doesn't seem to respond to the power key or any other, the screen is blank with no backlight and the display controls don't do anything.
When I hold the reset button on the back of the machine, the power LED goes off.
I've tried pressing the reset button for long periods of time (10-20s, 30-50s, etc) several times to try and reset the PMU but it doesn't seem to be making a difference.
I've tried this with the power supply on and off, but again no difference.
I've even tried it with the original NiMH battery pack (which is probably unusable by this point) connected, but again no difference.

Does anyone have any advice for me to try and get this thing working, please?

Thanks in advance

Adam

 

[TheMightyMadman]

Hi all,

I thought the external power brick was playing up as I wasn't measuring 24Vdc on the pads of the power connector on the mainboard, so I tried powering the mainboard from my current-limited benchtop PSU. I tried powering just the mainboard at 24Vdc making sure the polarity was correct and with the current limit set to 500mA, and it hit the current limit immediately, supplying only about 5Vdc.

I got my thermal camera out to take a look around the board to see if anything was getting hot, and sure enough PD1 (IR3H 60V 3A SMD Schottky rectifier diode) was getting pretty damn hot, I measured it in place and it was short-circuit, I removed it and measured it out-of-circuit and it was definitely short-circuit. I've ordered a suitable replacement part and I'll see if fitting it makes any difference.

Does anyone have a schematic for the 1400cs, or any useful information on the mainboard power circuit? Is the supply input fused?

Many thanks,

Adam

 

[MacUp72]

make sure the CPU,RAM and ROM boards are seated in firmly..do you have a spare CPU, maybe it is dead.
and when the Schottky was dead, something was causing this.

 

[croissantking]

I find the CPU to be particularly troublesome on these in terms of getting it to seat correctly.

The diode could have just failed due to age, as commonly happens on the PowerBook 100 series. Will be interesting to see if a new part gets it going again.

 

[MacUp72]

did you get the replacement Schottky yet? I guess you already tried connecting the power adapter and power on with pressing Control+Command+Power and immediately reset the PRAM on the first sound.

 

[TheMightyMadman]

Hi all,

I've fitted a new 60V 3A Schottky diode at PD1 (VS-30BQ060-M3), built my own 24Vdc 2.5A PSU using the connector from one of the possibly bad Apple PSUs, and reset the PRAM using the reset button on the back of the machine, and the PowerBook is now working again!

Thanks everyone for your help.

Many thanks,

Adam