T30 noise

[vlakci]

Hy - I searched under old topics but didn't had luck

I bought a T30 for car diagnostic reasons (RS232 connector, small to carry, fasten enough for new software, cheap parts, good quality). After a quick dust clean, checking for any broken parts, putting a better HDD I had under hand and a new operating system boot, I went on upgrading the RAM and found the common problem of solder points on one of the RAM connectors. Tested the possible pins causing the problem with a multimeter, soldered them and tested each RAM slot - it works. Then put a 256MB and 512MB I got at hand - but while doing this I noticed a strange thing.

While the computer is turned off (w/ or w/o battery) and pluged to the wall power I can some high pitch verry low volume noise bellow the RAM - in the corner which faces the miniPCI connector. By hearing close by, the noise comes from chip marked U76 (Toshiba) or near it or under it on the other side of the motherboard. This noise is not pressent when is turned off only with the battery pluged, or when the T30 is turned ON (on battery or only wall power). All other features run perfectly without problems, but I would like to be sure about the noise under the inner RAM.

[rkawakami]

Welcome to thinkpads.com!

U76 is a Toshiba TB6808F, a power supply controller for laptops. It's also used in A31 and T23 systems and probably other Thinkpads of that era. And that's about all I know about it. I had tried locating a datasheet for that part several years ago (ref: http://forum.thinkpads.com/viewtopic.php?t=37956) and I'm still coming up empty.

My guess is that what you are hearing is one of the inductors that is located nearby. I don't believe that an inductor is connected directly to the TB6808F, rather they are used by one or more of the other power controllers on the motherboard; typically Maxim chips like MAX16xx or MAX17xx or Analog Devices ADP38xx. If you are not familiar with what an inductor looks like, this image is a map of a T23 motherboard. Example of inductors are the black objects located at C5/C6 and G6, that are square in shape but have a round inner core and the black/blue object at D5. Inductors are usually marked on the motherboard using "L<number>". There's not much you can do to quiet them. You could try using a hot glue gun and encasing the inductor in molten plastic.

[vlakci]

There's not much you can do to quiet them. You could try using a hot glue gun and encasing the inductor in molten plastic.

that's a bad idea. Each inductor has 4 mayor details: size, inductance, max current at which the magnetic fiels is comming to the max (B/H hysteresis) and max current for max allowed heat disipation. Placing glue around or on it, would only limits air flow and can cause a overheating. If this problem causes the solder points to crack or the wire to lose it's furnish you can have a lot more problems. Basic coils can be replaced easly as only two solder point elements on a quite big pad.

I will check next time I have the keyboard and cover removed, if the big inductor near the ATI is causing the problem.

[vlakci]

I checked with the keyboard and bottom covers removed, but I could narrow the point of the noise. It could be under the heatsink, under the center keyboard (2 inductors) or above the RAM (didn't went to remove the plastic housing arround the keyboard). Tried to "noise out" (finger gently presed on coil) the two visible inductors around the power diodes but didn't help. For now I will not touch it further as the PC is working 100%, only when power to the wall and tuner OFF the strange low volume, high pitch noise.

[vlakci]

I think I found an error on the motherboard near the source of the noise. With the keyboard removed and looking on the PCMCIA slot, with the 4 screws holding it to the motherboard: a few mm under the bottom right screw of the PCMCIA right on the bottom end of the PCMCIA white slot connector, there are 3 SMD elements. two SMD are similar to a footprint 0603 or 0805 and a SOIC8 chip under them. The left SMD under the screw is a 0603 foil capacitor which had a bad solder, the right SMD is fully missing and I see visible traces of previous element on the SMD footprint (I think it was a diode SMD casing with think legs). Under this two elements then is the SOIC8 and under it then already starts the HDD enclosure.

Can any one check the marking on the SMD right of the capacitor and it's orentation (if diod it has a white sign on one side of the black casing), or even better if some one post a picture of the SMD between the bottom right corner of the PCMCIA and the top right corner of the HDD. Only needed part to be removed is the keyboard (2 screws)