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T43 network IC replacement

T40/T41/T42/T43 Series
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t43_guy
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Joined: Sat Jan 09, 2021 12:06 am
Location: Caracas, Venezuela

T43 network IC replacement

#1 Post by t43_guy » Sat Jan 09, 2021 12:40 am

Hello all, I have been reading these forums for 3 years now but I finally decided to join, thanks for this service guys.

TL;DR: will my T43 recognize the MAC address of the new BCM5751M or will it refuse to POST ?

I have an intel based T43 which I bought non-operational and slowly repaired the motherboard using parts from my other dead T43s, the last thing pending for a fix is the ethernet which currently only works sometimes (maybe for 24 hours or so after the computer has been turned on), after that it starts to misbehave and shows a lot of RX and TX errors, the workaround is disabling it in the BIOS. Now, I did some diagnosing and I'm fairly sure the problem is that the network IC, which is the Broadcom BCM5751M, is faulty, so I have to replace it, my problem is not getting a replacement since I have plenty of donor T43 motherboards, but rather that I'm not sure as if replacing this IC will make the machine unable to POST because this new IC has a different MAC address and thinkpads are quite picky when it comes to unique identifiers.

The network IC is connected to an EEPROM which is U33 (located near the broadcom IC) which holds some data that I'm not sure what it actually is, but from reading datasheets from other Broadcom ICs I think it only holds the PXE code and the device and vendor IDs which one can see issuing lspci on Linux, so there should be no problem in changing the broadcom IC because it contains its MAC and the BIOS should read the new MAC from it (?).

My question is, can I replace this IC and the machine will work as usual, using the new MAC address ?

Maybe someone here has experience about replacing network ICs in a thinkpad. Also I would appreciate if you can provide a link to the BCM5751M datasheet, I searched as much as I could but it seems that it isn't available online as it is a very old IC.
T43 Intel board PM-735 overclocked to 2.26 GHz 2 GB RAM
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ajkula66
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Re: T43 network IC replacement

#2 Post by ajkula66 » Sat Jan 09, 2021 1:04 am

Welcome to the forum!

The LAN card is integrated into the motherboard and is not meant to be replaced.

Getting a PCMCIA LAN adapter would be my advice.

Good luck.
...Knowledge is a deadly friend when no one sets the rules...(King Crimson)

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One FlexView to rule them all:A31p

RIP: T43pSF

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t43_guy
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Joined: Sat Jan 09, 2021 12:06 am
Location: Caracas, Venezuela

Re: T43 network IC replacement

#3 Post by t43_guy » Sat Jan 09, 2021 1:14 am

Yeah, I thought about a PCMCIA card but I want gigabit speeds :s
and gigabit Express cards are hard to find and expensive so I want to fix this thing

Thanks for your reply anyways ;)
T43 Intel board PM-735 overclocked to 2.26 GHz 2 GB RAM
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ajkula66
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Re: T43 network IC replacement

#4 Post by ajkula66 » Sat Jan 09, 2021 1:24 am

t43_guy wrote:
Sat Jan 09, 2021 1:14 am
Yeah, I thought about a PCMCIA card but I want gigabit speeds :s
and gigabit Express cards are hard to find and expensive so I want to fix this thing
$6.99 on Amazon...

https://www.amazon.com/NETGEAR-GA511-Gi ... B0002VITFU

I love the T4x generation but would advise anyone against dumping too much time and/or money into that platform nowadays.

YMMV
...Knowledge is a deadly friend when no one sets the rules...(King Crimson)

Cheers,

George (your grouchy retired FlexView farmer)

One FlexView to rule them all:A31p

RIP: T43pSF

Abused daily: T520, X200s


PMs requesting personal tech support will be ignored.

RealBlackStuff
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Re: T43 network IC replacement

#5 Post by RealBlackStuff » Sat Jan 09, 2021 1:27 am

You didn't search very much I guess (or used that crappy Google)
Use DuckDuckGo to search for: BCM5751M datasheet
The very first link is a PDF.

And then read this: /viewtopic.php?p=717184#p717184
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BillMorrow
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Re: T43 network IC replacement

#6 Post by BillMorrow » Sat Jan 09, 2021 1:31 am

how will you get anything into venezuela..?
just asking..

also, i don't know what "LA" means where you are but please edit your location to show where you are..
unless, that is, your government is watching and not approving.. :??:
Bill Morrow, kept by parrots :parrot: & cockatoos
Sysop - forum.thinkpads.com

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She was not what you would call refined,
She was not what you would call unrefined,
She was the type of person who kept a parrot.
~~~Mark Twain~~~

t43_guy
Posts: 5
Joined: Sat Jan 09, 2021 12:06 am
Location: Caracas, Venezuela

Re: T43 network IC replacement

#7 Post by t43_guy » Sat Jan 09, 2021 1:33 am

Yes, you are right RBS, but that is not a datasheet, it's a product brief and doesn't tell me what I need, I already removed the chip from another T43 and I'm just waiting to buy the BGA solder balls but I don't know their diameter, I'm gonna go for 0.4 mm and hope that works.

EDIT: I read the whole post you linked but I couldn't make any conclusions, I guess if the thinkpad complains I will replace the EEPROM as well lol
Last edited by t43_guy on Sat Jan 09, 2021 2:15 am, edited 1 time in total.
T43 Intel board PM-735 overclocked to 2.26 GHz 2 GB RAM
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t43_guy
Posts: 5
Joined: Sat Jan 09, 2021 12:06 am
Location: Caracas, Venezuela

Re: T43 network IC replacement

#8 Post by t43_guy » Sat Jan 09, 2021 1:34 am

oops sorry, I don't like disclosing my location publicly but I just noticed that it now shows up in my profile, I will change it now.
T43 Intel board PM-735 overclocked to 2.26 GHz 2 GB RAM
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kfzhu1229
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Re: T43 network IC replacement

#9 Post by kfzhu1229 » Sat Jan 09, 2021 2:29 am

t43_guy wrote:
Sat Jan 09, 2021 1:34 am
oops sorry, I don't like disclosing my location publicly but I just noticed that it now shows up in my profile, I will change it now.
I believe a rule on this forum is you must show your actual location, the reason why is to prevent spams (whether your IP address is in the blacklist of suspected bots or not for example).
The network IC on these things are in a BGA package. Replacing it means you have to reball and unless you are dealing with a T43p motherboard with FireGL graphics, it is simply not worth your time to perform a reball on especially the Intel iGPU motherboard.
Dell Lat CP MMX-233 64mb 40gb W2k
600 PII-266 416mb 40gb WXP
T23 PIII 1.13ghz 1gb W7
Precision M4300 X9000 8gb 160gb WUXGA Ultrasharp fp W10
T530i 15.6" i7 16gb fp W10
UXGA:
A30p PIII 1.2 1gb W7 (IDTech)
T43p 2.26 2gb fp W10 (Sharp)
Lat C840 P4-2.5 2gb 60gb W7 (Ultrasharp)

t43_guy
Posts: 5
Joined: Sat Jan 09, 2021 12:06 am
Location: Caracas, Venezuela

Re: T43 network IC replacement

#10 Post by t43_guy » Sun Sep 12, 2021 2:07 pm

Hey T43 Intel board reporting in with gigabit ethernet now!

After buying a bench power supply and solder paste I finally decided to disassemble the ThinkPad and try to fix it, I noticed there was a short circuit to ground on a power rail (VCC1R2AUX) which feeds the BCM5751M, then I found out that the faulty component was a little capacitor, I replaced it and now ethernet works :D

In the end replacing the network IC itself wasn't necessary so my original question remains unanswered, sorry.

Actually I prefer the Intel model of the T43 because it uses less power and heats up less than models with dedicated graphics, and those graphics chips are really weak compared to modern ones anyway, but I agree they are good for driving high resolution displays.

Ethernet has been working for a week without any problems, but just recently I discovered that my USB ports are not sending enough power, time to diagnose again :/
T43 Intel board PM-735 overclocked to 2.26 GHz 2 GB RAM
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kfzhu1229
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Re: T43 network IC replacement

#11 Post by kfzhu1229 » Sun Sep 12, 2021 2:40 pm

t43_guy wrote:
Sun Sep 12, 2021 2:07 pm
Actually I prefer the Intel model of the T43 because it uses less power and heats up less than models with dedicated graphics, and those graphics chips are really weak compared to modern ones anyway, but I agree they are good for driving high resolution displays.
I mean it is mandatory to drive high resolution displays. If you plug in a 14.1" SXGA+ screen or a 15" screen with higher resolution than SXGA+, it will simply not work at all.
And for many collectors the high res screens are part of the charm so that ruled out the Intel GMA board as well
Dell Lat CP MMX-233 64mb 40gb W2k
600 PII-266 416mb 40gb WXP
T23 PIII 1.13ghz 1gb W7
Precision M4300 X9000 8gb 160gb WUXGA Ultrasharp fp W10
T530i 15.6" i7 16gb fp W10
UXGA:
A30p PIII 1.2 1gb W7 (IDTech)
T43p 2.26 2gb fp W10 (Sharp)
Lat C840 P4-2.5 2gb 60gb W7 (Ultrasharp)

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