Is this old, obscure  Pentium laptop shorted? - Page 1
Forum section: electronics / beginners

author: bingo29
author_rank: Newbie
timestamp: April 13, 2025, 06:20:06 am
content: Hi! I'm new to electronic repair, anything besides replacing electrolytic capacitors is pretty much beyond my understanding. I've already posted this in the BadCaps forum , but haven't received any replies, hopefully someone here can offer some insight!I've purchased this weird (and might add appears to have had a fairly rough life) laptop a while ago for $1 at a yard sale. It powered up one time, (saw a POST screen!) Then, never powered again. I've since thrown it in some dark corner, BUT, I've decided to look at it again. First, this seems like a very obscure laptop, mine just has the name "BIT" on it and nothing else. Very similar (same?) can be seen herehttps://www.vogons.org/viewtopic.php?t=54655.At first, I had gotten the weird mini display on the lower part of the laptop to display a few icons, but if I attempted to power it on, the mini display went blank, the main display did nothing. I tried a few basic troubleshooting steps, consequently attempting to power the laptop on. But, at one point, when I plugged the AC adapter in, some form of short circuit protection seemed to kick in. Now it does it every time I connect power without even attempting to turn it on. The AC power block makes a strange noise, and the LED will turn off. Also noticed a bit of corrosion from the barrel battery although it's mostly on the opposite side of the board.I've started to remove some things from the laptop, thinking they were causing the short, the CD ROM, Floppy and HDD. No avail. Also this 'laptop' appears to have no battery.So, last thing I did was remove this tiny power board like thing, (?) and after that, the AC adapter no longer went into protection mode.. However, still not powering on.Beyond recapping motherboards and PSUs, this is above my levels . I vaguely recall reading about measuring the resistance too ground on the coils if something like this occurs, and on the 2 coils on the daughter board, one read, 3.8k ohms, the other was over 13k ohms. But honestly not sure what to make of that and I'm stumped!

author: metertech58761
author_rank: Frequent Contributor
timestamp: April 13, 2025, 07:15:02 am
content: I can't speak to the detail of the needed repair, but I know one thing: Those VARTA batteries are infamous for leaking and destroying boards.At minimum that battery needs to go. There are other modern replacements that are safer.

author: nightfire
author_rank: Frequent Contributor
timestamp: April 13, 2025, 09:36:47 am
content: From what I recall, the CPU is a standard Pentium CPU, as special mobile options were not really available at this time, at least not to normal end-users. So this could be a ZIF socket 5 or 7 with the standard Pentium CPU packaging as it was in pre-MMX days.So this notebook theoretically could have been planned not as a notebook, but without battery as a simple transportable workstation. Or someone removed the battery option some time ago due to issues.Your symptoms like not switching on could be due to faulty voltage regulator board at the input, also some battery leakage and corrosion probably give you some hassle.This means, that the corrosion should be cleaned off, and then the input side has to be checked if everything is ok here- depending on how the system is build there, the connectors might tell if there is/was any provision for a battery pack. Also depending on that, you could eventually power the notebook from an internal battery connector via a standard lab power supply.

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 13, 2025, 12:59:17 pm
content: QuoteDo you mean that it is missing the battery or that it doesn't appear to have a battery option?If the battery is missing this could cause the problem, I've seen laptops before that would not turn on without a battery.

author: squadchannel
author_rank: Frequent Contributor
timestamp: April 13, 2025, 01:11:35 pm
content: CMOS batteries, or resume batteries, used in PCs at the time were made of nickel batteries, which are very leaky. Macintosh(CRT era) is a famous example.If they leak out, as you can see from the picture, they corrode everywhere on the board.It is not likely to be fixed unless it is a historical PC.I had a tough time with the IBM Palmtop PC110.(yellow wiring is original)

author: calzap
author_rank: Frequent Contributor
timestamp: April 13, 2025, 05:10:01 pm
content: Being new to electronic repair, this is not a good first project for a successful outcome. The motherboard is multilayer and daughter boards and PSU board may be too. The problem is putting your soldering iron tip on the board and causing unnoticed damage or shorts. Desoldering and replacing caps falls in this category. I’ve successfully replaced caps on CBs, like on the infamous Samsung TV power supplies. But I had a computer motherboard with visually bad caps; it immediately went to recycling. There appears to be corrosion on the motherboard which is another strike against successful repair. Cleaning away corrosion and cleaning contacts is a good place to start. I agree the old Varta batteries were awful. Saw one damage the mainboard on a very expensive Metler ultrabalance; fortunately, the board was repairable.Exploring and playing with those computer boards can be fun and educational. Don’t get your hopes up for seeing a setup screen though.Mike

author: bingo29
author_rank: Newbie
timestamp: April 14, 2025, 08:40:19 pm
content: Thanks everyone! Yeah this appears to be designed without a battery, unless I didn't notice a location for battery contacts. There's also no physical room for a battery, but I'll look closer to see what I can find and if I can possibly connect my lab supply to it. I'm gonna start with cleaning the corrosion, removing the Varta battery, and I'll start probing the input with my DMM, and locate the voltage regulator chip and go from there.

author: bingo29
author_rank: Newbie
timestamp: April 14, 2025, 09:32:27 pm
content: Rapid update! So, just for funnies, I thought that maybe I'd try powering the laptop from my bench supply before I do anything else. So, I did what the OP did on Vogons, and the power supply sparked and current draw went way up, then I released the magic smoke. Upon closer inspection, I've discovered the culprit, I think it's a MOSFET. Possibly Siliconix? I couldn't seem to find a datasheet, or replacement. Even if I did, I'm afraid the replacement would blow tooLocated on the small power board, that plugs into the header towards the bottom of the main board, between the CD ROM and floppy drives. I think just the one appears to be blown. It appears to be labeled:4412AYW542