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Power problems - Toshiba T4600C laptops

J

JonnyGators

Experienced Member
Joined
Mar 9, 2020
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Attleboro, MA
I figured getting a working 486 laptop would be a fun little project, and a nice machine to have handy. So I settled on a Toshiba T4600C laptop.

The first one arrived with much damage to the case, as the idiot that shipped it put it in a padded envelop and trusted it to the post office like that. The seller apologized, gave me some story about someone else doing the shipping, and offered a partial refund, since after all it was a parts/as is listing. Ok....fair enough.

Found another cheap T4600 with a damaged screen, so picked that up for more parts, and non busted case, since it's essentially the same thing but without a color screen.

Well....both the darn things do the same thing, give me a P30 error code.

Luckily the service guide is out there, and has nice detailed instructions on disassembly.

The error indicates "B3V Voltage is over the maximum allowable limit."

Ok.....great......power supply issues. Why does it always gotta be power supply issues?

I've looked rather closely at both power supply boards, they both look fine. No leaking capacitors. Nothing at all jumping out as problematic.

I did find some postings about similar toshiba laptops referencing replacing a 1000uF capacitor. And I did find 1 1000uF capacitor on the board. Randomly changing 1 specific capacitor that shows no apparent problem because an ancient forum post about a similar laptop isn't exactly the best process for troubleshooting......but how in the heck do I chase down a laptop power supply problem with one vague error code and no visual problems?

I did attempt to replace the capacitor, but....this board is impossible to work on. I couldn't desolder it. I could only pull it off, leaving pins on the top side of the board. They wouldn't desolder off. It seems like it was pressed into metal contacts built into the board, not soldered on through holes in the board, leaving it impossible to put another capacitor on. So, I have 1 board with capacitors ripped off that won't take new ones, and one board untouched that still seems to result in the damn P30 error that tells me nothing useful with no way to figure out the problem.



Am I the proud owner of a big pile of trash that used to be 2 laptops, or is there any hope for building a working laptop out of these?
 
FWIW if you have two pins sticking up, you can solder the capacitor to the pins on top. It's not ideal but works.
I can't really help with the P30 issue though, the only Toshiba's I've repaired were the 1900 series where they'd just turn back off immediately on startup.
 
That won't work on this board....the board connects to another board, and mounting the capacitors on the pins, making them take up more height, will block the board from connecting to the other board. I had bought a few different values of capacitors to try and replace a bunch of them and see if I could get something working, but some of the capacitors are taller than the one they are replacing, and will not fit in even if I could manage to find a way to replace them.

This board is impossible.

Unless anyone has any working methods to fix up these power supplies....I'd have to say, these laptops just aren't viable for anything useful anymore from what I'm seeing. Nice to have thrown my money away on garbage. This just seems to be my luck....everything I buy has power supply issues that are impossible to fix, because no one seems to be able to figure out how to design anything that will actually work for a decent amount of time...
 
JonnyGators said:
Unless anyone has any working methods to fix up these power supplies....I'd have to say, these laptops just aren't viable for anything useful anymore from what I'm seeing. Nice to have thrown my money away on garbage. This just seems to be my luck....everything I buy has power supply issues that are impossible to fix, because no one seems to be able to figure out how to design anything that will actually work for a decent amount of time...
Click to expand...

There's actually some truth to that. I can assure you it's not your luck, it's a PSU design flaw that affects almost every 486 based Toshiba laptop.
Toshiba's Pentium-based laptops corrected this flaw and are generally much more reliable in my experience. (however some of their later Pentium-based laptops, namely the Tecra series IIRC have an entirely different design flaw where the stress of plugging and unplugging the power cord can actually crack the motherboard!)
 
You're going to have to find a way to replace the 1000uF 6.3V capacitor. 2cm tall x 8mm in diameter or smaller.

I believe most Toshiba laptops from that era all use a very similar power supply, with only slight differences. The power supply from the similar T1900C for example, has the same voltages but the 1000uF capacitor is soldered on through holes in the board.

If you can't replace the capacitor on either of the power supplies you already have, try getting a power supply from a similar model Toshiba laptop. As long as it has the correct voltages and connectors, it should work fine even if the design is slightly different.
 
I'm not convinced that 1 capacitor is the problem. There are several capacitors on the board, all same manufacturer, no physical evidence of damage. The only evidence that I've found of that capacitor being the issue is someone making a vague reference to replacing a capacitor of that value on a similar laptop years ago.....not exactly the best method of troubleshooting power supply problems.

I guess no one here knows how to fix power supplies, other than randomly replacing capacitors and hoping for the best?
 
JonnyGators said:
I'm not convinced that 1 capacitor is the problem. There are several capacitors on the board, all same manufacturer, no physical evidence of damage. The only evidence that I've found of that capacitor being the issue is someone making a vague reference to replacing a capacitor of that value on a similar laptop years ago.....not exactly the best method of troubleshooting power supply problems.

I guess no one here knows how to fix power supplies, other than randomly replacing capacitors and hoping for the best?
Click to expand...

It's not "randomly replacing capacitors and hoping for the best" - like I said in my first post, it's a known problem with earlier Toshiba power supplies. Over time, the capacitor dries out and can no longer hold a charge, even if there's no obvious signs of damage.

That being said, I suppose it could be one or more of the other capacitors - but in almost every instance I've seen it was the 1000uF capacitor.
 
JonnyGators said:
......I guess no one here knows how to fix power supplies, other than randomly replacing capacitors and hoping for the best?
Click to expand...
I'm sure there is people here that have the experience and knowledge of how to fix PSU's, The problem is trying to fix them " Long distance ", A multitude of things can go wrong in a PSU and not show any signs of damage / failure and if you don't have the right tools or know how to properly test capacitors / components one may think a component is good when it may not be, Not to mention the danger's of messing with PSU's.
 
All power supplies are different. There is no single, guaranteed solution that will fix them all.

If replacing that cap fixes most of them, why not at least give it a try? It really couldn’t hurt at this point.

You started this thread to fix the laptop, right? Okay, so you have gotten advice on replacing a capacitor that has fixed other Toshibas with similar issue in most cases. Sounds like a good start to me. No, it’s not a 100% guaranteed fix, but NOTING is when dealing with almost 30-year-old electronics. Patience is also key to success here (and with anything really).
 
I tried changing that capacitor, although I'm not sure I didn't do damage with the change due to the layout of the board making it nearly impossible to do a capacitor change, but with the new capacitor it still reads the same error. No change at all!
 
I guess my point is, I don't think it's accurate to say that changing that specific capacitor has fixed it in most cases. I found 1 old forum post that someone changed that capacitor, and a 2nd post that someone else tried it. Although it only references the capacitor value, for all I know there's another capacitor somewhere on a board with the same value. Or values of capacitors can vary between similar models perhaps.

It just feels like it's a real shot in the dark to be changing capacitors based on a very small sampling of rather old forum posts that only reference a single capacitor value. I guess I feel like, I swapped a random capacitor with no solid evidence of it being a problem, and a voice in my head is asking myself "well....why did you expect that to make any difference?"

Not to mention, it wasn't exactly a smooth operation to solder in a replacement capacitor to a board that didn't just have holes that the old capacitor smoothly came out of with desoldering. I had to pull the old capacitor off, and try to force through the leads of the new capacitor. And even then, when I went to check it again, the board didn't really take the solder, the new capacitor was wiggling around in place easily.

That's why I"m at a point where I consider the board I "replaced" a capacitor on probably damaged, and my 2nd untouched board a possible 2nd chance.....if there were any real suggestions on this thread other than "yeah....try changing the capacitor.....that we have no evidence is actually a problem.....and will likely irreversibly damage the board trying to do.....so you can have 2 broken boards"
 
I can understand why you're frustrated, especially after having spent money on these computers, believe me I've been there.

Other users on this thread have given some good advice. Like Malc and compaqportableplus said, there's no guaranteed fix when it comes to these old electronics, and a multitude of things can go wrong inside a PSU. I suggested replacing that capacitor based on what I've personally seen, I've seen it fix these Toshiba power supplies but it's not a guaranteed fix in every case.

At this point you have two options. You can either try and replace that capacitor on the second board you have (though I can understand if you're hesitant to do so) or you can track down a known working PSU. I'm sure you've already seen this website, which has a list of some of the 486-based Toshiba laptops. The power supplies in these models should be interchangeable, making it easier to find a replacement PSU.

Some other options include finding other methods to troubleshoot the boards you already have (though if you don't have much experience with high-voltage electronics I would stick to replacing that one capacitor or completely replacing the PSU) or seek an alternative 486-based computer.
 
The power supply board itself is small and easily shipable. Heck....a put together laptop is easily shipable. It would make far more sense to not senslessly destroy a 2nd power supply with a fix not based on actual troubleshooting and diagnosing, and instead somehow get this board to someone that can properly run diagnostics and repair it.

I was hoping there would be people in online communities that could actually assist with things like this. Advice is great. I'm not opposed to taking on new challenges and picking up new skills. But there comes a point where certain parts are best left to people with the proper skills. I was hoping to find people I could pay for some repairs.

But instead I've found no one with any such skills here. Or at least none of them are speaking up. Just a bunch of random suggestions to try changing random capacitors until things work. No science, no troubleshooting, no diagnosing......just random changing of capacitors and hoping for the best.

Can anyone offer anything better than just repeating the same random capacitor suggestions that have already destroyed one of these boards?
 
Make a thread asking for help here:

http://www.vcfed.org/forum/forumdisplay.php?30-Vintage-Computer-Services-Offered-Needed

It really hard to troubleshoot something that’s not physically in front of you. You may never get it working. That’s just how it goes sometimes. I’ve got two early Toshiba laptops that I was never able to fix, and even posted a thread here about it. Nobody really knew exactly what the problem was, and that’s fine. I’m not angry at anyone for that. Nobody has located the fix for those yet. Plain and simple.

We are a smaller group than most, so keep that in mind. It’s not like every other person in the world know how to repair this stuff.

Also, some people don’t have the time to take in items for repair, and some just don’t want the liability of working on someone else’s stuff, because you’re always gonna have that hard-ass that’s never happy.
 
I've got a T4600C as well (and the DeskStation II), and also had the P30 issue. Replacing the capacitor fixed that problem (and disassembly/reassembly of those notebooks is very painful). Unrolling the power supply PCBs was a new experience for me...

But I have a weird power problem now: I can turn the notebook on and off like normal, but after some time (a few hours, sometimes less) the device turns on and I can't turn it off until I completely unplug the power. Plugging it back in instantly turns it on again. This behaviour also appears if the device is inside the docking station (also turns on the docking station). I have no idea what the problem is.

Both the notebook and the docking station haven't been used for a long time until I fixed the P30 issue. In the meantime, the soundcard (used for the CD-ROM) had failed, but soon after I had to pack it up to make some space for the home office... anyway, I would like to get the system back to working, but don't know where to start.
 
Hello. Since today, I have this laptop too and it also shows me the P30 error message. I was successful in opening up the case. No battery leakage so far.
 
I fixed a toshiba 4700 that was showing a P30 error by replacing all of the capacitors on the power board.
 
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