• Please review our updated Terms and Rules here
  • Exhibitor application for VCF West 2022 is now open! If you are interested in exhibiting, please fill out the form here.
  • Here are the results of the VCF East 2022 Post Event Survey: Survey Results

Toshiba T3200SX power supply troubleshooting

Dagwood

Experienced Member
Joined
Oct 16, 2018
Messages
55
I picked up a T3200SX that won't power on. There is no DC output at all from the power supply and a beautiful squeal. I'm still working my way through the circuit but my question is... When the power supply is functioning normal, which is the power good signal? Or does it not have one?

1 M-12V
2 M-5V
3 GND
4 P+12V
5 GND
6 GND
7 VCC
8 VCC
 

GiGaBiTe

Veteran Member
Joined
Apr 30, 2015
Messages
2,724
Location
Austin, Texas
If it's squealing, I'd check the main line capacitor(s) first, they've probably failed. They're the big cap(s) on the primary side usually rated between 250-450v.

Not all power supplies had a power good signal.
 

Dagwood

Experienced Member
Joined
Oct 16, 2018
Messages
55
Not all power supplies had a power good signal.

Okay, that's what I was wondering. Maybe the PSU waits until stable to output, or maybe it's just a free for all! Regarding the troubleshooting... The caps look very nice and the ones I've tested check out. I may get back to them later but I've found a bad MOSFET so I'm examining that and any potential collateral damage. Thanks for the input.
 

GiGaBiTe

Veteran Member
Joined
Apr 30, 2015
Messages
2,724
Location
Austin, Texas
You'll need to check all capacitors, just because they look nice doesn't mean anything. Capacitors can look physically OK but have any number of fault conditions, such as high ESR, being open or short or leaking out the bottom rubber seal.

A capacitor tester which can show capacitance and ESR is needed to verify a cap. A capacitor should nominally be within a small margin of its rated value, but electrolytic caps have a +/- 20% tolerance and can be a bit higher. ESR should also be low, if its more than a few ohms for larger capacitors then the cap is bad. There are ESR charts available online.

MOSFETS don't usually go bad on their own, something else most likely killed it. I'd suspect faulty capacitors, resistors or diodes.
 

Dagwood

Experienced Member
Joined
Oct 16, 2018
Messages
55
You'll need to check all capacitors, just because they look nice doesn't mean anything. Capacitors can look physically OK but have any number of fault conditions, such as high ESR, being open or short or leaking out the bottom rubber seal.

MOSFETS don't usually go bad on their own, something else most likely killed it. I'd suspect faulty capacitors, resistors or diodes.

Yep, I understand, that's why I said I may get back to checking the other caps and that I am assessing other potential damage. Busy week at work and home though so I had to set it aside for a week, maybe longer. I'll try to report back when I make progress. Thanks.
 

wowbobwow

Experienced Member
Joined
Mar 20, 2015
Messages
56
Location
Bay Area, California
Hope it's okay to bump an older thread! I just recently acquired a Toshiba T3200SXC (details of my machine here) and it's in great shape visually but won't power on beyond a click and the Power LED briefly flashing. Dagwood - were you ever able to get your Toshiba's PSU rebuilt? I'm an experienced retrocomputing collector/nerd but I'm a total beginner with soldering and electronics, so I'd be grateful for any guidance you might have gleaned from your experience - especially if you happened to assemble a "shopping list" of replacement capacitors and/or any other parts needed to bring your machine back to life. Thanks!
 

kerr

Member
Joined
Oct 21, 2021
Messages
27
Location
Melbourne, Australia
My advice would be to consult the maintenance manual (minuszerodegrees?) so you know what voltage each wire/lead should produce. Like Dagwood said, it's going to be something like 12v, 5v, GND etc. Make sure you're at least getting those readings using a multimeter.

Regarding building a new PSU (assuming it really is the PSU at fault), it's probably not for the faint of heart... However depending on the output voltage requirements, you might be able to rig up an external power brick like this:


Just my 2c 🪙
 
Top