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Tube🍂Time

this power board is a sea of discrete circuits. what a pain to reverse engineer.

200 comments
Joviko Wi

@tubetime

Kind of big on parallel caps going to ground. Bet that looks cool.

Tube🍂Time

looks like the only electrolytic capacitor on the board had leaked, and the electrolyte etched and broke 6 vias. let's see if my repair worked...

Tube🍂Time

the SCR doesn't fire anymore, and the 5V standby rail works!

Tube🍂Time replied to Tube🍂Time

there's something wrong with the LCD but the system is trying to boot!

Tube🍂Time replied to Tube🍂Time

with an external monitor connected, we can see it's unhappy about some stuff, but it's running code, so that's pretty cool.

Tube🍂Time replied to Tube🍂Time

more bad electrolytic caps hanging out in the LCD electronics.

Darryl Ramm replied to Tube🍂Time

@tubetime

Therapist: So you have nightmares about electrolytic capacitors?

Patient: Yes.

Therapist: And they are following you around?

Patient: Yes.

Therapist: And you think they want to harm you?

Patient: I know they do.

Tube🍂Time replied to Tube🍂Time

oh boy, the LCD looks fantastic! this is a big step forward.

Eric Vitiello replied to Tube🍂Time

@tubetime I loved that thinkpad. such a solid machine! And the nipple mouse was super.

Tube🍂Time replied to Tube🍂Time

I'll need to figure out how to fix the hinge mounts. they were very weak in the original design, and the hinges stiffened up, so when someone opened it up, the plastic just shattered.

Tube🍂Time replied to Tube🍂Time

i also need to figure out how to fix the error codes, but that should be simple.
00016100 - CMOS battery
00016300 - Time and date
I9990303 - System boot partition failure (I pulled the HD)

Tube🍂Time replied to Tube🍂Time

the coin cell is the regular CMOS battery, and the other battery is for standby mode, I think. it probably maintains the RAM contents during a main battery swap.

Tube🍂Time replied to Tube🍂Time

i should mention how i fixed the very stiff hinges in the Thinkpad 700C. i supported the hinge and hit the shaft with a hammer (red arrow). this backed out the locking washer and reduced the pressure on the hinge stack, and therefore the friction.

DELETED replied to Tube🍂Time

@tubetime looks like big clive bench lolol

Jeroen Ruigrok van der Werven replied to Tube🍂Time

@tubetime Problems solved by whacking with hammer: *adds one to the tally*

Tube🍂Time replied to Tube🍂Time

I've installed a new coin cell. yes I soldered wires directly to the cell 😬

Tube🍂Time replied to Tube🍂Time

this is neat, the front panel has an indicator LED that can be configured to light up when the speaker makes a noise.

Tube🍂Time replied to Tube🍂Time

ok it stopped working again, something with the power board. i'm doing more reverse engineering. this is barely half the board!

Attila Kinali replied to Tube🍂Time

@tubetime I'm not sure, but I think your sheet size is a tad bit too small for your schematic

Tube🍂Time replied to Tube🍂Time

this is fascinating: the power board has several laser trimmed resistors (sure, pretty common) but these have been laser trimmed AFTER being soldered onto the board!

[DATA EXPUNGED]
marble 🔮 replied to Tube🍂Time

@tubetime got something bigger to hold on to and also electrical connections for measuring. this way they maybe also compensate for variance in the production process

Attila Kinali replied to Tube🍂Time

@tubetime Huh? On a power supply board? What sub-circuit are these resistors part of?

Tube🍂Time replied to Attila

@attilakinali there are 7 of them. they trim the output voltages and a few other parameters

DELETED replied to Tube🍂Time

@tubetime VR3 - variable resistor? Are those fine tuned via the laser?

Tube🍂Time replied to Tube🍂Time

now i am repairing some more vias. the capacitors leaked and etched out a bunch of vias. this one needs to be connected on layer 2, so i had to remove some copper pour and FR4 to expose the trace.

Jeff Haluska replied to Tube🍂Time

@tubetime What camera do you use to take these macro shots?

Tube🍂Time replied to Jeff

@jhaluska just my phone. i have a Moment case with a small macro lens

Tube🍂Time replied to Tube🍂Time

ok i have a theory about why this was failing. symptoms: randomly the computer would shut off and pull a ton of current...

1) crowbar circuit fires. it can fire due to a rail going overvoltage...

2) a buck converter's MOSFET wasn't switching properly...

3) oh look this diode wasn't connected anymore due to a bad via!

Michael Kohne replied to Tube🍂Time

@tubetime I'm guessing they trimmed to tune the system as a whole, not just the single resistor value?

Jake replied to Tube🍂Time

@tubetime My first job out of school was doing fpga stuff at a company that did laser trimming. It was wild. They used analog circuits to drive the galvos which had the mirrors. If the circuitry was off by a bit, you could see the “ringing” of the circuits in the right angle cuts (instead of an angle you’d see a little degrading sine wave). I’m still convinced analog EE’s are wizards.

Ian Scott :apple_inc: 🐙 replied to Tube🍂Time

@tubetime the one and only time I soldered directly to a coin cell it exploded in my face. Never again!

Ali Mirjamali replied to Tube🍂Time

@tubetime You need a small spot welder in your arsenal (and so do I)

yuriy opryshko replied to Tube🍂Time

@tubetime I’m too scared to do that, so I use electrical tape to tape the wires to the cell (plus cover the whole thing with said tape so it looks similar to the original)

John Lindsay replied to Tube🍂Time

@tubetime doesn’t the coin cell run the RTC?

Fritz Adalis replied to Tube🍂Time

@tubetime
Are you going to install Windows 3.1 or OS/2?

Larionov replied to Tube🍂Time

@tubetime
If you will want to attach anything to original plastic I found that apart from bolting together the best way would be to weld plastic with a fine steel mesh like here in the video. youtu.be/KJTrNINAs0o

You can just use a regular soldering iron for this and for the small parts you'll need a finer mesh, can find it on amazon amazon.com/dp/B0B3T3ZBSR . Holds much better than the glue

Matt replied to Tube🍂Time

@tubetime that's what happened to mine, but also the plastic has gone extremely brittle.

jgeorge replied to Tube🍂Time

@tubetime What’s your process for this? Yours always turn out great!

Tube🍂Time replied to jgeorge

@jgeorge lots of flux, heat, and endless scrubbing with IPA.

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