I need to disconnect an EEPROM Chips Vcc, should i desolder it or just cut Vcc? - Page 1
Forum section: electronics / beginners

author: jorgp2
author_rank: Newbie
timestamp: April 15, 2017, 05:29:41 pm
content: When i was updating my laptops BIOS, it got bricked. I don't have the serial information, i don't want to send it off for several weeks to be serviced, and i enjoy fixing things myself.So i bought a Mini Pro TL866A, but i cant program the EEPROM while its still plugged in because the rest of the bard draws power away from it. I can either trim Vcc and bridge the gap with solder, or i can desolder the whole thing and resolder it afterwards.I do want to get into soldering, so i was already planning to buy a soldering iron and some other equipment. But my main question right now is if i need a heat gun or hot air station to desolder the IC, its just an 8 pin DIP with plenty of room around it.Or would it be easier and cheaper to just cut Vcc and fill the gap with solder.Sorry if my spelling is bad, i'm used to my laptops keyboard for typing.

author: sokoloff
author_rank: Super Contributor
timestamp: April 15, 2017, 07:04:35 pm
content: I have the equipment to desolder, so that's the way I'd go, but it will be easy to snip and later reconnect Vcc.One question is whether another pin will also be problematic (a reset or chip select pin may also have interactions with the motherboard). That's why I'd lean towards desoldering, but if you can't, your plan seems worth a shot.

author: TrickyNekro
author_rank: Frequent Contributor
timestamp: April 15, 2017, 07:36:36 pm
content: You better desolder the whole thing, rather than cutting only the Vcc. You can not know if the IC connected to the EEPROM has:1. ESD protection diodes, which probably it has as it is a CMOS device so it´s a no - no!2. the ports of the IC are open collector, which if not it´s impossible to write to the EEPROM by controlling the data clock lines when the laptop is powered.So as you can see it get´s rather complicated to do it without desoldering the memory. But as far as I am aware, there EEPROMs are usually in SO - 8 packageson purpose, so that it is easy to service the bios.Now I noticed: You said DIP package... In a laptop? That´s a first, how old is the laptop? I´m asking out of curiosity. In that case a soldering iron, a desolder pumpand maybe some solder wick is the way to go. But have some practice first on an old PCB, or else it can be not so nice.A lot of times, laptops have a bios ROM (like Lenovo laptops) which can be recalled by a key combination to restore the EEPROM. Are you sure yours doesn´t havesomething like this? In some motherboards you even get something liike a pre-bios utility that can flash the IC directly from a flashdrive. Are you sure yours hasnothing of the said above?Cheers,Lefteris

author: jorgp2
author_rank: Newbie
timestamp: April 16, 2017, 10:20:53 pm
content: Sorry its a SOP8 Package.Its a lenovo thinkpad, but the bios recovery doesn't seem to work, any idea what the process is?

author: Ian.M
author_rank: Super Contributor
timestamp: April 17, 2017, 12:51:46 am
content: I strongly suspect you've misidentified the BIOS. An 8 pin package memory chip would usuilly be some sort of serial interface I2C or SPI device, usually EEPROM. However PC BIOS chips are almost invariably medium to high pin-count parallel interface memories. They used to be EPROMs or OTP PROMs, but are now most commonly FLASH devices. x86 class processors need parallel memory for their BIOS code. The only exception would be S.O.Cs with a built-in SPI bootloader or similar.

author: Monkeh
author_rank: Super Contributor
timestamp: April 17, 2017, 03:14:16 am
content: Quote from: Ian.M on April 17, 2017, 12:51:46 amYou're a little out of date. Nobody uses parallel flash on an x86 platform today - haven't for years. Especially in laptops!Here's a random motherboard:https://www.quietpc.com/images/products/ga-h97-d3h-large.jpgSpot the parallel flash.

author: Ian.M
author_rank: Super Contributor
timestamp: April 17, 2017, 03:21:11 am
content: Well, I learned something new today. Thanks for the correction.I assume that reading the presumably SPI FLASH into memory is a chipset function, or have Intel and their competitors added a SPI interface and logic or microcode that copies the boot image into on-chip cache?

author: Monkeh
author_rank: Super Contributor
timestamp: April 17, 2017, 03:23:46 am
content: It is indeed a chipset function, one integrated into SoCs when needed. They're also capable of pulling boot code from a PCI bus.You can't have things like the integrated NICs on chipsets without an SPI flash - makes little sense to have a honking big parallel piece on LPC as well. Support for multiple devices is built in to most, too.

author: jorgp2
author_rank: Newbie
timestamp: April 17, 2017, 06:35:45 pm
content: Mmm, my EEPROM Reader wouldn't read it. But when I soldered it back on to the board the laptop booted up just fine.Any ideas on what I did to fix it?

author: ebastler
author_rank: Super Contributor
timestamp: April 17, 2017, 07:46:23 pm
content: Quote from: jorgp2 on April 17, 2017, 06:35:45 pmMaybe you disconnected/shorted the CMOS battery in the process, and have reset your BIOS settings to default?Anyway, congratulations on not having bricked the laptop! I must say that I got a bit nervous when you mentioned that you wanted to "get into soldering", and try desoldering the EEPROM as your first project. Glad to hear that it turned out well!

author: jorgp2
author_rank: Newbie
timestamp: April 17, 2017, 08:26:42 pm
content: But I had already tried resetting the bios, it was bricked it wouldn't even try to post.

author: chriswebb
author_rank: Unknown
timestamp: April 18, 2017, 09:53:01 pm
content: Is the POST saying anything helpful when you try starting up the computer? With a dead CMOS battery, I've seen many boards give warnings during POST. Maybe yours is too?

author: jorgp2
author_rank: Newbie
timestamp: April 20, 2017, 05:17:03 pm
content: No, works 100% fine now