Motherboard Repair: NOT Replacement Anyone?

[t20user]

I have a bad T22 board it seems. It shows signs of a bad power supply section: it boots up after sitting for a long time, but if I try to re boot nothing happens, 2 LEDs light breifly and no boot.

The question is has anyone around here actually replaced the so called bad capacitors on a dead mobo? Does anyone here debug the mobo instead of tossing it and replacing it with one from ebay?

I am a hardware EE, and I have excellent circuit troubleshooting skills. I also have access to very good solder rework stations. If I find out what is wrong with mine, I might be interested in helping/buying other boards.

[freddy418]

bad power supplies can very well be due to short circuited capacitors or blown diodes. You can try replacing the capacitors, but then what about the dead diodes? However, if you have an IBM reference manual for T22 motherboard interconnects and a plethora of microelectronics components, it might take a while, but there's no question that you can do it.

[t20user]

I have access just about any passive component I might need, if it is an IC I might have it. I do not have schematics or the reference manual you refer to. I would have to rely on my troubleshooting skills.

Now if there are common component failures or trouble spots on these T20-22 boards then I could fix more than one easily. Does anyone want to donate a dead board to the cause?

[mrastudent]

You must have a LOT of spare time because what you're thinking of doing is only seen in the movies. Component by component checks with a multiple-layer circuit board?

[t20user]

I think you are missing the point of my post mrastudent: I dont have a LOT of time on my hands, that is why I wondered if anyone knew of a particular trouble spot on these boards. If it has already been teked out by someone I can save some time. Or even better a list of reference designators that are commonly bad.

And it isn't only seen in the movies: if you know the right technicians it can be done, anything is possible.

[AbsoluteRaleigh]

I am curious as well.

Where I work we replace around 10 - 20 T2* boards per week.

At one point someone purchased a bunch of our bad T20-T22 boards and they told me that often the boards have a bad cap on them. More specifically, when a T20 develops the infamous HD blink issue (when the power button is pressed, the HD light blinks, and that is IT)- is supposed to be a bad cap or an “overloaded cap.” A lot of rumors float around the net w/ misc “tricks” from tapping a power button hundreds of times to refrigerating your laptop until the problem goes away.

Here we haven’t tried many of these tricks as many are just nonsense. I have wanted to experiment with them but we get the boards so cheap (in qty) it just hasn’t happened yet. Someday we’ll sit down and experiment with replacing some components to see what happens

All I can say for sure is a certain electronics company purchased a lot of 50 bad boards from me a while back. After a month went by I asked them if they were interested in more and they said no. So, maybe the “overloaded capacitor” rumor floating around on the net is bogus. Who knows? I have yet to see anyone repair the bad boards, or at least for less amount of $ than it takes to replace the boards.

What I do know is good boards are worth $100 and bad ones sell for $10 and that the bad ones are not in high demand. If anyone figures out how to fix them I would be thrilled to find out how or sell them to that person so that they can make some $...

So, t20user, I wish you luck with locating and replacing the bad component- if you successfully do that, I would really be interested in hearing about your results.

BTW- on occasion, we’ll get a T20/T21 in here that hangs at the BIOS screen. Sometimes, starting it up w/out the CMOS battery will cure the issue, but it is 50/50…

And as for the HD blink issue, it appears to be more common in the T20 and T21 than in the T22, and I haven’t seen it on a T23, ever…

[verktyg]

Thanks for all of the info. A few months back I replaced the mainboard in my T20. It started having the blinking problem about a year ago - right after I read several messages about others experiencing the same problem.

The problem acts like there is a bad capacitor in the start up circuitry because some systems will work for a while after they sit for several hours to several days. An IBM tech support person mentioned this possibility to me when I called to see what it would cost to have the mainboard replaced.

It could also be a defective diode or transistor in the circuit that keeps one or more of the caps charged until they bleed down and the system starts up again - for a short while.

A few folks have been lucky and replacing the CMOS battery fixes the problem.