FuST wrote on 2020-12-20, 14:43:

I am documenting the entire process and will release it to my YouTube channel when I'm done.
I also made a vieo describing how the PSU board actually works which I will release somewhere in the following weeks.

Thank you for documenting everything. I'll be waiting for your videos 😀

ConventionalMemories wrote on 2020-12-21, 16:03:

Wow, that's some amazing work. Thank you for reverse engineering that board for us all. What where the most common components t […]
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FuST wrote on 2020-12-20, 14:43:

I have updated the schematic slightly as I noticed some errors while fixing the first machine's PSU board, V1.1 is included as a […]
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I have updated the schematic slightly as I noticed some errors while fixing the first machine's PSU board, V1.1 is included as an attachment.

I am documenting the entire process and will release it to my YouTube channel when I'm done.
I also made a vieo describing how the PSU board actually works which I will release somewhere in the following weeks.

T1600 PSU Schematic (v1.1).pdf

Wow, that's some amazing work. Thank you for reverse engineering that board for us all.
What where the most common components to fail in your experience? Might help me repairing my two T1600's

You mentioned looking for an XT-IDE solution, I have a Compact Flash adapter up for sale that fits in the expansion slot with XTIDE rom on board. It can also be configured to control the internal IDE controller. https://www.benl.ebay.be/itm/264877993192
If you're interested I'd be happy to send you one for free as a thank you for all the hard work.

Now next up the T1200 and T3100sx. 😉
(They appear to have similar power board issues, recapped, no signs of corrosion, check all vias, no sign of life. Power LED blinks red when trying to power on)

Thank you very much!

First let me answer your question. This will be a bit lengthy as I'll explain what I found wrong with my boards.
The most common components are obviously the capacitors. This is, as you probably already know, a problem for all Toshiba laptops from the late 80's/early 90's. My T1200XE and all 3 of my T1000LE's suffered the exact same problems.
In fact, I would go as far as to say that when you get a late 80's/early 90's Toshiba you shouldn't even plug it in. Just take it apart immediatly and replace the caps to prevent more serious damage.

One thing to note here is that these caps are part of a switchmode powersupply (buck, boost and buck/boost converters) so replace them with name brand, high-temp, low-esr ones (I used Panasonic and Würth).

The T1600/40's PSU board actually had nothing else wrong with it component-wise, it just had two broken traces.
The T1600's PSU board had a lot more wrong with it.
Before I got it Q29 was already destroyed, as well as C38.
There was a trace broken between the negative side of C4 and the trace going off to PJ2 (main connector).
There were also traces broken between R135 and PJ3 pin 1 (R135 is part of a voltage devider to sense the battery voltage) and between R137 and a via hole leading to IC13 (R137 is a pullup resistor).

I started desoldering the power MOSFETS so I could put them into my component tester and found Q3, Q4 and Q5 to be defective.
Mosfet #2 of IC5 (pin 3 input, pin 18 output) was damaged, it wouldn't turn off fully in a test setup.
Finally, the diode I mentioned in my last post.

A lot of other components died in the testing process, partly because of my stupidity in not verifying my work properly and not powering off the board when testing with my multimeter.

The irreplaceable parts (the IC12 & IC13 MCUs and the IC3 gate array) are pretty well protected, anything else is still somewhat available, if you are willing to order stuff from DigiKey/Mouser and AliExpress.
The only thing I can't find besides one webshop in Italy is the ceramic resonator for IC12 (X2) but unfortunately they require a minimum order of €30,- and the component is only €0,50 so one of my T1000LE's has to do without one for now.

As I said in my previous post, I really suggest getting a storage oscilloscope. It will allow you to visualize what the board is doing and if all the voltage rails come online.
It also comes in handy when trying to see if the MOSFETS and the transistors driving them are actually switching properly, things like a broken diode or transistor will show up way easier than trying to measure everything in-circuit.

I'd be happy to take some screenshots on my scope at certain points on the board to show what it should look like.
In fact, I might even just do that and add it to the schematic PDF, along with some text explaining how the thing works.

Pfeeewww, that's a wall of text isn't it?

Now, on the subject of a XT-IDE.
I actually noticed your boards a while back when you posted about them on Reddit and was considering buying one for the T1600/40. The JVC harddrive is kind of an odd beast and chances of repairing it are slim to none.
You offering to send me one for free has me at a bit of a loss for words to be honest, that is very generous and kind. It's something I never expected when I uploaded the schematics so they might be of use to other people in the community.
I'm definitely interested in one and really appreciate the offer. Could you send me a PM so we can talk about shipping, etc?

Having typed all this, if anyone has any questions regarding these PSU boards, I'm happy to help out where I can.
This was a challenging, fiddly, time-consuming and at some times very frustrating thing to do but man is it satisfying when it finally works.
After all, it's just electronics. Anything is fixable with the right tools, knowledge and a lot of spare time 😜

FuST wrote on 2020-12-22, 17:09:

Thank you very much! […]
Show full quote

Thank you very much!

First let me answer your question. This will be a bit lengthy as I'll explain what I found wrong with my boards.
The most common components are obviously the capacitors. This is, as you probably already know, a problem for all Toshiba laptops from the late 80's/early 90's. My T1200XE and all 3 of my T1000LE's suffered the exact same problems.
In fact, I would go as far as to say that when you get a late 80's/early 90's Toshiba you shouldn't even plug it in. Just take it apart immediatly and replace the caps to prevent more serious damage.

One thing to note here is that these caps are part of a switchmode powersupply (buck, boost and buck/boost converters) so replace them with name brand, high-temp, low-esr ones (I used Panasonic and Würth).

The T1600/40's PSU board actually had nothing else wrong with it component-wise, it just had two broken traces.
The T1600's PSU board had a lot more wrong with it.
Before I got it Q29 was already destroyed, as well as C38.
There was a trace broken between the negative side of C4 and the trace going off to PJ2 (main connector).
There were also traces broken between R135 and PJ3 pin 1 (R135 is part of a voltage devider to sense the battery voltage) and between R137 and a via hole leading to IC13 (R137 is a pullup resistor).

I started desoldering the power MOSFETS so I could put them into my component tester and found Q3, Q4 and Q5 to be defective.
Mosfet #2 of IC5 (pin 3 input, pin 18 output) was damaged, it wouldn't turn off fully in a test setup.
Finally, the diode I mentioned in my last post.

A lot of other components died in the testing process, partly because of my stupidity in not verifying my work properly and not powering off the board when testing with my multimeter.

The irreplaceable parts (the IC12 & IC13 MCUs and the IC3 gate array) are pretty well protected, anything else is still somewhat available, if you are willing to order stuff from DigiKey/Mouser and AliExpress.
The only thing I can't find besides one webshop in Italy is the ceramic resonator for IC12 (X2) but unfortunately they require a minimum order of €30,- and the component is only €0,50 so one of my T1000LE's has to do without one for now.

As I said in my previous post, I really suggest getting a storage oscilloscope. It will allow you to visualize what the board is doing and if all the voltage rails come online.
It also comes in handy when trying to see if the MOSFETS and the transistors driving them are actually switching properly, things like a broken diode or transistor will show up way easier than trying to measure everything in-circuit.

I'd be happy to take some screenshots on my scope at certain points on the board to show what it should look like.
In fact, I might even just do that and add it to the schematic PDF, along with some text explaining how the thing works.

Pfeeewww, that's a wall of text isn't it?

Now, on the subject of a XT-IDE.
I actually noticed your boards a while back when you posted about them on Reddit and was considering buying one for the T1600/40. The JVC harddrive is kind of an odd beast and chances of repairing it are slim to none.
You offering to send me one for free has me at a bit of a loss for words to be honest, that is very generous and kind. It's something I never expected when I uploaded the schematics so they might be of use to other people in the community.
I'm definitely interested in one and really appreciate the offer. Could you send me a PM so we can talk about shipping, etc?

Having typed all this, if anyone has any questions regarding these PSU boards, I'm happy to help out where I can.
This was a challenging, fiddly, time-consuming and at some times very frustrating thing to do but man is it satisfying when it finally works.
After all, it's just electronics. Anything is fixable with the right tools, knowledge and a lot of spare time 😜

Once again, some very useful information. This will come in very handy once I have the time to get out my t1600's.

And yes the capacitors are a real issue on these.
In terms of the power supplies in my experience: the T1000 and T1100(+) aren't affected,
From what i've seen the problems start with every battery powered model starting with the T1200. (t1600 t3100sx)
I haven't had any problems with any of the AC powered ones, apart from a RIFA cap here and there. (t3100, t5100, etc.)
The early 90's models have capacitor issues as well but they dont seem to take all the other components with them when they fail, making them much easier to repair with a recap, some corrosion cleanup and trace repairs. (T1000le t1200xe t4400 t1910 etc.)

So from what I have seen the 3 that are the hardest to repair are the T1200, T1600 and T3100sx.
I'm not really confident I have the electronics skills to get any of these working, although with this schematic and some learning I't might be time to invest in an oscilloscope and get a bit more in depth. Otherwise if I cant get them working I had been thinking of making some replacement psu boards with some basic of the shelf buck converters, without any of the charging or stand-by circuitry shouldn't be too hard. I had them running once from a bench power supply.

Also, what model JVC drive does the T1600/40 have? mine are both regular t1600's.
If I remember correctly I might have a spare working 40MB JVC RLL drive from a T3200 with a broken gas plasma display.

ConventionalMemories wrote on 2020-12-23, 02:55:

Once again, some very useful information. This will come in very handy once I have the time to get out my t1600's. […]
Show full quote

FuST wrote on 2020-12-22, 17:09:

Thank you very much! […]
Show full quote

Thank you very much!

First let me answer your question. This will be a bit lengthy as I'll explain what I found wrong with my boards.
The most common components are obviously the capacitors. This is, as you probably already know, a problem for all Toshiba laptops from the late 80's/early 90's. My T1200XE and all 3 of my T1000LE's suffered the exact same problems.
In fact, I would go as far as to say that when you get a late 80's/early 90's Toshiba you shouldn't even plug it in. Just take it apart immediatly and replace the caps to prevent more serious damage.

One thing to note here is that these caps are part of a switchmode powersupply (buck, boost and buck/boost converters) so replace them with name brand, high-temp, low-esr ones (I used Panasonic and Würth).

The T1600/40's PSU board actually had nothing else wrong with it component-wise, it just had two broken traces.
The T1600's PSU board had a lot more wrong with it.
Before I got it Q29 was already destroyed, as well as C38.
There was a trace broken between the negative side of C4 and the trace going off to PJ2 (main connector).
There were also traces broken between R135 and PJ3 pin 1 (R135 is part of a voltage devider to sense the battery voltage) and between R137 and a via hole leading to IC13 (R137 is a pullup resistor).

I started desoldering the power MOSFETS so I could put them into my component tester and found Q3, Q4 and Q5 to be defective.
Mosfet #2 of IC5 (pin 3 input, pin 18 output) was damaged, it wouldn't turn off fully in a test setup.
Finally, the diode I mentioned in my last post.

A lot of other components died in the testing process, partly because of my stupidity in not verifying my work properly and not powering off the board when testing with my multimeter.

The irreplaceable parts (the IC12 & IC13 MCUs and the IC3 gate array) are pretty well protected, anything else is still somewhat available, if you are willing to order stuff from DigiKey/Mouser and AliExpress.
The only thing I can't find besides one webshop in Italy is the ceramic resonator for IC12 (X2) but unfortunately they require a minimum order of €30,- and the component is only €0,50 so one of my T1000LE's has to do without one for now.

As I said in my previous post, I really suggest getting a storage oscilloscope. It will allow you to visualize what the board is doing and if all the voltage rails come online.
It also comes in handy when trying to see if the MOSFETS and the transistors driving them are actually switching properly, things like a broken diode or transistor will show up way easier than trying to measure everything in-circuit.

I'd be happy to take some screenshots on my scope at certain points on the board to show what it should look like.
In fact, I might even just do that and add it to the schematic PDF, along with some text explaining how the thing works.

Pfeeewww, that's a wall of text isn't it?

Now, on the subject of a XT-IDE.
I actually noticed your boards a while back when you posted about them on Reddit and was considering buying one for the T1600/40. The JVC harddrive is kind of an odd beast and chances of repairing it are slim to none.
You offering to send me one for free has me at a bit of a loss for words to be honest, that is very generous and kind. It's something I never expected when I uploaded the schematics so they might be of use to other people in the community.
I'm definitely interested in one and really appreciate the offer. Could you send me a PM so we can talk about shipping, etc?

Having typed all this, if anyone has any questions regarding these PSU boards, I'm happy to help out where I can.
This was a challenging, fiddly, time-consuming and at some times very frustrating thing to do but man is it satisfying when it finally works.
After all, it's just electronics. Anything is fixable with the right tools, knowledge and a lot of spare time 😜

Once again, some very useful information. This will come in very handy once I have the time to get out my t1600's.

And yes the capacitors are a real issue on these.
In terms of the power supplies in my experience: the T1000 and T1100(+) aren't affected,
From what i've seen the problems start with every battery powered model starting with the T1200. (t1600 t3100sx)
I haven't had any problems with any of the AC powered ones, apart from a RIFA cap here and there. (t3100, t5100, etc.)
The early 90's models have capacitor issues as well but they dont seem to take all the other components with them when they fail, making them much easier to repair with a recap, some corrosion cleanup and trace repairs. (T1000le t1200xe t4400 t1910 etc.)

So from what I have seen the 3 that are the hardest to repair are the T1200, T1600 and T3100sx.
I'm not really confident I have the electronics skills to get any of these working, although with this schematic and some learning I't might be time to invest in an oscilloscope and get a bit more in depth. Otherwise if I cant get them working I had been thinking of making some replacement psu boards with some basic of the shelf buck converters, without any of the charging or stand-by circuitry shouldn't be too hard. I had them running once from a bench power supply.

I think I haven't been active for long enough here to send PM's. But you can send me a message at ConventionalMemories@gmail.com
Also, what model JVC drive does the T1600/40 have? mine are both regular t1600's.
If I remember correctly I might have a spare working 40MB JVC RLL drive from a T3200 with a broken gas plasma display.

That's similar to my experience, though I do not have a T1000 or T1100(+) so I can't say anything about those.

I thought about creating a replacement PSU with some buck converters but a quick search on the main connector turned up nothing and I really wanted the original board to work.
It's been a learning process for me as well. I have some basic electronics skills but greatly improved them while learning about DC-DC converters and op-amps through YouTube (there are some great explanations on there!). See it as an oppertunity to increase your skill level.
When using off-the-shelf converters keep in mind they should be able to deliver enough power at the correct voltage.
From the T1600 maintenance manual (table 1-5 on page 1-10):

1FUNCTION                                      DC VOLTAGE      TOLERANCE(%)          CURRENT
2-----------------------------------------------------------------------------------------------
3System logic, FDD
4HDC, HDD                                      +5              +-5                   1850mA
5-----------------------------------------------------------------------------------------------
6HDD logic                                     +5              +-5                    350mA
7-----------------------------------------------------------------------------------------------
8Backup RAM                                    +5              +-5                    200mA
9-----------------------------------------------------------------------------------------------
10LCD VEE                                       -22             +-5                     10mA
11-----------------------------------------------------------------------------------------------
12RS232C, Modem, IO-slot                        +12             +-10                    40mA
13-----------------------------------------------------------------------------------------------
14RS232C, Modem, IO-slot                        -9              +-10                    40mA
15-----------------------------------------------------------------------------------------------
16Backlit EL                                    +12             +-10                   400mA 

The 12V seem to all be connected together on the PSU board, same goes for the 5V lines, with the exception of the backup RAM.
Also, the HDD uses 12V even though it's not listed in the maintenance manual. It requires about 1 amp (peak) when powering up.

The harddrive in the T1600/40 is a JVC JD3848H01-1A. It uses a 26-pin JVC connector and dedicated controller board with a ROM.
According to my research it should be a RLL drive. It's an odd beast, made for OEMs.
Please see the attached pictures.

Edit: Thought I'd add a bit on the JVC.
It does spin up after powering it a couple of times, the heads do a seek and the drive seems to initialize. The controller's ROM seems to function correctly, allowing me to choose the drive type.
After selecting the correct type the machine just goes into a boot loop. It tests the memory and then (probably) tries to initialize the drive and just reboots. No floppy seek, no nothing.
The machine works fine with the Conner drive and controlle r from the T1600.

FuST wrote on 2020-12-23, 06:34:

The harddrive in the T1600/40 is a JVC JD3848H01-1A. It uses a 26-pin JVC connector and dedicated controller board with a ROM. A […]
Show full quote

The harddrive in the T1600/40 is a JVC JD3848H01-1A. It uses a 26-pin JVC connector and dedicated controller board with a ROM.
According to my research it should be a RLL drive. It's an odd beast, made for OEMs.
Please see the attached pictures.

Edit: Thought I'd add a bit on the JVC.
It does spin up after powering it a couple of times, the heads do a seek and the drive seems to initialize. The controller's ROM seems to function correctly, allowing me to choose the drive type.
After selecting the correct type the machine just goes into a boot loop. It tests the memory and then (probably) tries to initialize the drive and just reboots. No floppy seek, no nothing.
The machine works fine with the Conner drive and controlle r from the T1600.

Weird that it just reboots, if I remember correctly from the JVC disk in my T1200 it does initialize the drive controller before the FDD seek, when the drive wasn't working correctly an error message would be displayed after the memory count, something along the lines of disk controller failure or failed to initialize.

Just dug up the drive from the T3200 and although it is a 40MB RLL drive it's actually made by Fujitsu, model: M2227DT

Weird thing is that it actually also has a similar 26pin interface to its controller card, maybe there was some form of standard?

I must've been confused between this one and the one in my T1200 which uses a very similar JVC disk (model nr: JD3824G01-4) I think this is the 20MB model from the same family of drives.

It might be a standard also used by Fujitsu, though the signals will probably be different.
The JVC drive uses what is basically an ST-412 interface but without the twisted pair: https://knm.org.uk/blog/2017/04/the-jvc-26-pi … terface-part-1/
A quick Google search on the Fujitsu doesn't produce anything useful, unfortunately.

I'll investigate further on the JVC drive issue once I finish restoring the outside of the machine. Might be something simple.

Well, I be damned. The JVC drive actually works flawlessly.

The BIOS seems to be overridden by the JVC controller.
As I have removed the CMOS battery (it was dead and slightly leaky) and the system asks for a harddrive type when powering on.
It then lets you choose from 3 different drive types, two 42MB types and one 21MB type. None of these work, the machine just enters a bootloop as I described before.
BUT; you also have the choice of pressing F5 to load defaults. Didn't really seem necessary to try that option as you only have the three non-working options to choose from.

Well, apparently the "defaults" hide a fourth option, the only one that actually works. smh.
Choosing that option booted me right into a German MS-DOS 6.20 and the machine runs like a charm.

In the meantime I'm editing all the ~100GB of video material to be released to my YouTube channel and received the XT-IDE card from ConventionalMemories which works like a charm. Thank you very much for that!

He also sent along his two PSU boards so I can take a look at them. I'll be filming the entire process and put that up on YouTube as well so everyone can see my process.

That's great news 😀
Will be waiting for the release of the videos 😁

The first video is finally up, they will be released every friday at 4:00 PM CET.
They can be found on my YouTube channel, the first video can be found here: https://www.youtube.com/watch?v=K_-vP0P0AxU&t=51s

FuST wrote on 2021-01-29, 16:01:

The first video is finally up, they will be released every friday at 4:00 PM CET.
They can be found on my YouTube channel, the first video can be found here: https://www.youtube.com/watch?v=K_-vP0P0AxU&t=51s

Finished watching your video, it was enjoyable 😀

I hope that you'll manage to clean all the PCBs with alcohol, except in the areas with stamps (sometimes I clean of stamps with alcohol by mistake 🙁 I always try to preserve the stamps if the boards are not damaged in the area where the stamps are).

About the rust underneath the plastic, that will be hard 😒 I really don't know what you should do.
Maybe try to use a small nail file between the plastic and the rust?
In last resort, I think that you should deliberately break some of the solder points of the plastic to the case so that you can reach the rust and remove it.
After removing the rust, I would probably wash that part (including the wires that are attached) with hot water and dish soap in the bathtub, after that I would rinse in distilled water (to remove all minerals from tap water), dry with an hair dryer, rinse in alcohol, dry all small holes with rolled toilet paper and finally leave it several days drying alone.

But these are just suggestions, hope that you find simpler ways to restore that laptop.

I'll be waiting for the 2nd video.

Thank you very much!

The PCBs cleaned up nicely with minimal effort, though the PSU board did require a couple of wash cycles with vinegar and alcohol unfortunately removing any stamps and the serial number sticker.
The rust on the RF shield was a different story, the plastic is moulded onto the metal so it is impossible to clean in between. I did end up solving it in a different way but I won't spoil anything 😀

In the mean time I'm working on a troubleshooting guide for these boards, including some scope images. I'm hoping to have that available in the coming days.
Having tested another two boards also enables me to give a better answer to ConventionalMemories' question, which might help @brassicGamer as well:

ConventionalMemories wrote on 2020-12-21, 16:03:

What where the most common components to fail in your experience? Might help me repairing my two T1600's

In my experience it is mostly the DC-DC converter MOSFETs that blow. If they weren't so expensive and hard to get my advice for @brassicGamer would be to replace them all.
The troubleshooting guide should prevent you having to order ~ €40,- in MOSFETs from China by narrowing down which ones have failed.

Watched your second video. Good work 😁

I'll watch the 3rd and 4th video this weekend.

Thanks.

FuST wrote on 2020-12-20, 14:43:

So, after months of measuring, verifying and ordering a lot of new components and de- and resoldering 90% of the board I now have a working T1600 and a working T1600/40.

This is amazing. I'm looking forward to inspecting my board and seeing if anything you've discovered helps. I have reached the point where I have repaired all the broken things I have as much as I can, and will need a scope to go further. Hopefully I can find an old, good one cheaply!

Well, you don't _really_ need an oscilloscope but it does make it a lot easier.
You can desolder all through-hole transistors/MOSFETs and test them but that can be a bit of a pain, especially when the solder is corroded.
You can test the diodes using a multimeter, that should give a pretty good indication. They should have a ~0.5V forward drop and >1V reverse drop (due to measuring in-circuit).
I would probably also visually inspect the inductors (carefully remove the shield and glue it back on if they're o.k.). On one of ConventionalMemories' boards I found they had melted and charred.

My theory is that when the capacitors start to die the controller over-compensates with PWM regulation which in turn eventually kills the MOSFETs and/or the diodes.
When the MOSFETs fail short they can melt the smaller inductors.

Most damage I found were broken traces around the area where the capacitors are (due to electrolyte leakage) and damaged components involving the buck/boost converters, so MOSFETs, diodes, capacitors and inductors.
I have seen one or two damaged uPA1600's but only in cases where other things were also severely damaged.

So I've started watching your videos and followed the troubleshooting guide document - this was incredible, and a real bonus! I found only one broken trace out of the pointers that you provided. When I got to testing the voltages, I noted that there was 12V at Q14, but nowhere beyond. I checked the schematic, tested the traces from the MOSFET (which were fine) and removed it. It was giving me some strange readings so I think it's faulty. Typically I only have N-channel MOSFETs in stock, so I will have to order replacements.

Thank you so much for all your work, as it has made the difference between me making progress on this project or throwing it in the bin in frustration. I also have a T1200XE with similar problems and although I've replaced the caps and fixed the traces, there is some other problem that I feel more confident in eventually being able to fix. If I do get this thing working, I'll report with photos 😀

It's great to see others making progress repairing their T1600's, it would be a real shame to see these cool and quite innovative machines end up being scrapped.
To be honest, I'd like to salvage all old 8086 through 80386 Toshiba laptops I can get my hands on but then space is becomes an isssue.
I see this as my (indirect) way of saving them and providing back to the community that helped me throughout the years as well.

I'm very busy at the moment renovating my new house and preparing to move in next weekend so replies to your comments on the YT video's may be delayed a bit.
I look forward to seeing some pictures of your revived T1600 when the time comes, I'm confident you can repair it. Cheers!

I think we are working towards a point where we can have a generic guide on repairing these laptops. I have 5: a T1000 (repaired), T1200XE (not working), a T1600 (in progress) a T4850CT and a T4700CT (neither working). My Pentium Toshibas work brilliantly (a Satellite 320CDT and Tecra 740CDT), so these models obviously benefitted from lessons learned.

The first time I tried to repair a Toshiba power board, I had real trouble desoldering components, particularly because of the nature of the solder. At the time (this was about 5 years ago) I thought that a higher temperature would help. I had my soldering iron turned up too hot and I ended up damaging the PCB. This entire task is definitely suited to 'intermediate' level where skills and experience are concerned, and having an actual soldering station with pump definitely helps.

So far, the steps that I can see are as follows:

1) Remove through-hole caps. Use lots of flux and be patient because the old solder does not flow easily. The 'adding new solder' trick often doesn't help here. Do this one-by-one, noting on a list the designation e.g. C4 and values e.g. 25v, 220uF.
2) Remove through-hole MOSFETS (designator Q), diodes (no designator, just a number) and power transistors (designator IC), as these seem most prone to failure given that the higher amps flow through them. Again, do individually. Because these parts usually have a model number, I lay them out on a piece of paper, writing their designation below.
3) Treat board for battery corrosion / electrolyte leakage using a vinegar bath.
4) Test components from 2 either using a component tester or multimeter as appropriate. Make a note of which components function or not. Order replacements as required.
5) Remove any remaining solder from the holes and clean up messy areas with IPA.
6) Using magnification, inspect the board systematically looking for any problems. This includes SMT components that have visibly failed or are damaged, or traces that are broken.
7) Follow traces leading from the removed components to their destination and check continuity. Use troubleshooting guide and schematic if available.
8) Make any necessary repairs.
9) Install working components and test.

Beyond this point, more in-depth troubleshooting is required at the level FuST has been working at. Maybe at some point we will have more schematics for other models. Using this process I have identified two dead MOSFETS, and have confirmed that everything else should work. I'll have to wait for parts.

That list of steps to take looks pretty complete to me.
Part of the problem why the "add new solder" trick doesn't work is because the old solder is corroded by the electrolyte from the capacitors.
I find that scratching a bit of the corroded material off to expose some shiny solder and adding lots of flux usually does the trick.

Failing that, using a hot-air station or paint stripper works pretty good to heat up any internal ground planes prior to desoldering.

I'm actually working on a set of T1000XE's at the moment that have very similar issues, the PSU section of the board is pretty similar in all 8086-802086 type machines so I can probably whip up a schematic for that machine pretty quickly.

hi FuST,
How did the T1000XE restoration go? I'm embarking on same. Some caps were definitely bad and leaky but no PCB damage that I have found so far.

The first T1000XE wasn't that hard to fix, replacing a couple of capacitors and some minor PCB repair did the trick.
I started work on the second machine I got but haven't got around to finishing it, real life kind of got in the way.

I did start work on a T1000 which confirmed my thoughts on all the T-series machines having a similar architecture for the PSU section.

If the PCB looks good you're probably going to be okay with just replacing the caps in the buck/boost converters (i.e. the larger ones). The switching MOSFETs/transistors can take quite a beating on these.