TiBook LCD driver(?) chip fried, could use some help with ID

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dankephoto's picture
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TiBook LCD driver(?) chip fried, could use some help with ID

I've got a 667 DVI TiBook with a burnt SMT IC on its MLB, and I'm pretty clueless as to how to ID the damn thing. I've got some info from other similar MLBs but I still wasn't able to zero in on even what sort of chip it is, let alone what I could use to replace it.

PCB label says Q23 . . . I'm just guessing but does Q# mean a transistor? Yeesh, I can solder but I still don't know jack s**t about this kind of stuff! Biggrin

Anyway, take a look and if you can help I'll be most grateful:

http://mywebpages.comcast.net/macdan/tifriedchip.html

dan k

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My first guess would be that

My first guess would be that its an Op-Amp of some sort. Transistors are generallly 3 legged parts, not 6. Although this could be a type that I am not familiar with. All the transistors I am use to are 3 legged parts, as they only have a single gate. An Op-Amp is a DC amplifier and is generally in a 6 or 8 pin package (in my experience). And from the looks of it, there must have been some form of a short as it would take a decent amount of current to smoke one like that. I would pull that one off, and ohm out the pads that it was soldered too. Make sure there isnt a short (the part may have shorted internally rather then an external short). If it ohms out ok, then I would replace it with one from another boad, be sure its put in the right direction, and hope for the best Wink

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I'd just swap one from a dead

I'd just swap one from a dead mobo.

dankephoto's picture
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dead MLBs mebbe not really dead?

I'm pretty confident with my soldering ability, but not so with my unsoldering skills. I'm afraid I'd bugger up the chip getting it off the board.

Another thing with pulling a chip from one of the two 'supposedly' dead boards is that I'm not quite sure they're actually dead. After testing the 1gHz board twice, I'm pretty sure it's toast, but as it's a pretty valuable board if it can be revived, I'm loath to chop it up just yet. The 867 board also has potential value, it sort of powers up, fans and HD spin up, but no chimes. The shop manual says 'Replace MLB', but I'm not yet convinced. Thrifty and stubborn bastard am I.

So you see, if I could just buy a $.36 part instead of defiling another MLB . . .

Heh heh, OK, here's a question!

I have a couple of 100mHz dual-trace scopes laying about. Is there any way to use a scope to figure out what the chip does (using a working 'Book of course?) Just include complete directions on using scopes for electronic problem diagnosis please! Biggrin

dan k (have scope(s), am clueless)

jt
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Quartz?

Could it be a crystal? The pinout and traces seem possible for something like that? Have you looked up the little "crown" logo?

jt :?

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I havent ever seen a crystal

I havent ever seen a crystal in a bakelite package before. Crystals are almost always in a metal can packaging.

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Fixed!! with parts from "hanger queen"

I hated to swipe the parts from one of the (maybe) dead "hanger queen" MLBs, but in the end that's what I did. Worked out great, I'm posting this from a "new" DVI TiBook. :coolmac:

Before doing the swap I checked the voltages at the pins on my own DVI TiBook, it looks like this chip feeds voltage to the LCD's driver board. I'm betting the LVDS cable got pinched or something and short-circuited that feed.

T'was a bugger to de-solder and resolder though, very small parts, damn glad I have those magnifying glasses.

To recap, the symptom was an all-white screen with no image on it at all, 'Book otherwise working normally. Cure was to replace the six pin SMT IC at Q23. I also replaced the cap at C225, not sure if I needed to but had the part.

dan k

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more details - for completeness :)

Just adding some details for completeness for those who may stumble across this thread in the future trying to solve the same problem.

:mac:

A known good Q23 looked like this to my VOM, measured to ground (use this pic as reference:)
http://mywebpages.comcast.net/macdan/images/toasted_sot23/nice_sot23a.jpg

(this end closest to J17)
3 6
2 5
1*4

#s 1,2,4,5 = +3.29V
via a black something?? which jumps to J17 LVDS connector pins 1 + 2 (red stripes on cable)
# 3 appears to be the supply(?), +3.33 v
# 6 +1.7 mV (to ground? measures ~200K ohms to a "real" ground.)

#s 3 and 6 are connected by C225 - what's this do I wonder?

I still don't know the Q23 part ID (a voltage regulator maybe?), nor the value of C225 (cap color = value?? light tan = ??) Can anyone tell me what a "Q#" labeled part is on a PCB? (ie: regulator, transistor, etc.) And how do I measure a cap's value? I've got a cheap digital autoranging VOM (shows infinite resistance through loose cap), as well as a couple of decent 100mHz 'scopes which I don't know how to use (boy I love flea markets!) Any way to discover values using a scope?

dan k

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may not be an op-amp...

Well, the TI (TAS3004) chip is you Digital Audio Processor (with CODEC). Details on this chip can be found at http://focus.ti.com/lit/ds/symlink/tas3004.pdf. I would suggest you use a simple continuity tester to determine what pins (page 1-4) touch the failed part, from there and the notes, you may be able to backtrack to the part. Page 3-2 does indeed indicate usage of a dual Op-Amp (Dual High-Performance, Low-Voltage) and specifies the equivalant TI part number, but this part is an 8-pin IC.

HOWEVER, I did some deeper digging to try and ID the part manufacturer. According to Allied Electronics (http://www.alliedelec.com), the part appears to be an "Analog IC low-voltage single-pole/double-throw switch in a TSOP6 package". You can find one of these at http://www.mouser.com (800-346-6873), part number dg9431dv. They go for about $1.30 each and you may be able to get them to sample out a part to you or you may have to haggle for a low minimum order as some of these parts houses have minmums on the quantity of a part and/or the dollar value.

Proceed with caution, try to get you hands on a repair manual and check the schematic to see if there is any clues therein, also trace the part back to nearby ICs and see which anwer makes more sense.

HTH
--DDTM

EDIT: your pics helped!

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re: may not be an op-amp...

DDTM, nice references, thanks!

However, the blown chip, while right next to that loverly TI chip, is (I think) a switch that turns on and passes through the power to the LCD's driver board. Not related I think to the audio.

I did however use the Mouser.com search feature to scan for other possible SOT23 chips, and found . . .

Power MOSFETs! eg: http://www.mouser.com/index.cfm?handler=displayproduct&lstdispproductid=561409

"Power MOSFET Transistors SOT-23-6L N-Ch 30 Volt 4 Amp"

Does (or can) a MOSFET be used to switch on/off a power circuit? For all I know, that is what they do . . . :?

The above chip has the right pinout for "my" chip, but as I don't even understand the diff between a "P-Ch" and an "N-Ch" type transistor, I'm still pretty damn close to clueless. Still, this is as close as I've gotten to tracking down this F(*^*(&% chip.

Yee-F*&^ing-Ha!! :ebc:

dan k

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I'm quite sure that the chip

I'm quite sure that the chip you're looking for is called TL431.

It is a shunt voltage reference and is used in a lot of switching power supply designs. It gets often fried like in your pics - but sometimes not alone. So you have to check for other parts that are damaged. Just cut off the legs, solder a new TL431 on and look if it works. If not, check the other parts around, the resistors and Cs too.

While I'm at it and have seen your hp with the PB-display infos:

I have a PB G4 400 MHz. The display has 3 vertical stripes (1 pixel green) in different locations that disappear when I bend/flex it. Has anyone seen something like this and is it repairable? Or should I go hunting for a new display right away? Where would I get it?

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Try reseating the ribbon cabl

Try reseating the ribbon cables. Sounds like one is loose.

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re: I'm quite sure that the chip

mactechie - thanks for the TL431 clue, but I've not been able to find a chip that matches what I've got. Of course, that doesn't mean it ain't out there but exhaustive searching of Mouser.com and digikey.com came up empty.

dan k

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chip IDed (I think)

Leo Bodnar wrote me thusly and I hope he doesn't mind as I quote him:

LBodnar wrote:
. . . fried chip on http://mywebpages.comcast.net/macdan/tifriedchip.html is most probably the MOSFET that works as a switch to supply 3.3V power voltage to connector J17 (via inductor L43)

I can't find the exact manufacturer part number but this* could be quite a good drop in replacement for it. Even marking is very similar. The key on yours is "43", while 1DA is most probably manufacturing date/location. Also, pin 1 is where the white dot is near C777 and then clock counter-clockwise just like any other chip.

* ON Semiconductor
NTGS3443T1
Power MOSFET
2 Amps, 20 Volts
P−Channel TSOP−6

Well, looking at the above referenced chip and other similar chips it certainly looks like Leo has hit the nail on the head. It's exactly the circuitry of the fried chip. And at a cost of under US$1 per chip it'd be an economical repair.

My only question - as an electronics idiot, I'm not sure I understand the voltage rating, 20V in the above example. The voltages I measured on the TiBook were in the 3.3V range, so for the exact chip to use, do I need a specific part that outputs that 3.3V, or does something else control the specific output voltage?

Thanks Leo!

dan k

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MOSFETs

Well, here it goes...

MOSFETs have quite diverse application but in this particular case it is used as a voltage-controlled resistor. Or, rather switch. Or solid-state relay if you want. Let's have a look at the datasheet, what could be more adventurous reading? Smile
http://www.onsemi.com/pub/Collateral/NTGS3443T1-D.PDF

P-channel MOSFET is a reversed version of N-channel one (think PNP in bipolar transistor equivalent) and since N-channel was accepted as a "standard", all major voltages and currents in the P-channel device datasheet are negative to stress this difference. Why N-channel is a "standard"? Because out of two devices N-channels yield much better characteristics and are cheaper. Why? Because the N<->P symmetry is not fully so: N-channel conductivity is electron-based and P-channel is hole-based. Electrons are faster and better. No, they are not cheaper, but making N-ch MOSFETs is easier Smile If designer has a choice, he (or, maybe she?) will always chose N-channel design over P-channel unless there is no choice like in our case.

P-channel device passes the current from Source to Drain and N-channel from Drain to Source. Now, back to the datasheet.
When MOSFET is on (=open/conducts), maximum allowed current through it is Id = -2.2A
When on, its internal resistance is only Rds(on)=0.065 Ohm, think about it, isn't this amazingly low?
When it is closed (=off), maximum voltage allowed between Source and Drain is Vdss=-20v, otherwise it will break
To switch it on, one needs to bring Gate voltage at least Vgs(th)=-0.95v below Source.

So, if your Source voltage is +3.3v, then grounding Gate will create Vgs=-3.3v and that will fully open MOSFET, passing up to 2A of current from Source to Drain. There is no internal limit on this current, if you pull more than that, it will overheat and blow up. (Next slide...:)

Connecting Gate to Source (Vgs=0) will fully close MOSFET. How fully? Well, page 2 says only Idss = 1uA trickle through - that is ridiculously small current!

So, Dan, think relay here, maximum rating says not to exceed 20v and 3.3v fits just nicely there.

P.S. If you ask what that diode is doing inside your MOSFET, it is a by-product of manufacturing process and actually does not affect normal operation as it is wired "against" the normal current. However if you occasionally have reverse current spike (like when switching on a real relay or inside switching DC-DC converter) that diode very nicely work where external part would normally be needed to protect MOSFET from breakdown. This is a very rare case when something is free and useful at the same time!

P.P.S. The part is manufactured by many companies and they usually give them "look-alike" names, say Fairchild has similar Si3443DV, however the original chip from TiPB can be from a very small company to try to chase. Shop around and look for:
TSOP-6 package
P-channel
pinout
Max current (the more the better), Si3443DV is 4A
Max voltage, 20V is enough!

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C225...

C225 is a decoupling capacitor so really any value should work. The reason it is used there is because isolated gate MOSFETs have a nasty tendency to VHF oscillation if used "bare". The cure is a ferrite bead over gate pin on bigger packages, small value resistor in series with gate pin or a decoupling capacitor as in our case.

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