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Sceptre X9G Komodo monitor - Identifying a transistor

I'm developing a love / hate relationship with SMD devices. I love them when they work, and even when a parts list is available. When they don't, and one isn't, they cause a lot of grief.

This particular project is a Sceptre X9g Komodo VII A monitor. This is a 19" LCD monitor. I'm the second person on the project. The first earned my admiration by reassembling the monitor after pulling the power supply / inverter. He even left all the screws in the appropriate holes!!

After reassembling the monitor for test purposes I discovered it briefly (about 1 second) dimly flashed something on the screen, then blanked it. After some exploration, I located a bad solder joint on a film capacitor in the inverter. Resoldering this didn't fix it, it seems two transistors are shorted base-emitter. For what it's worth, this design is similar to the inverter used on Dell E172FPb and E173FPb monitors. A significant difference, the Dell uses through hole transistors (2SC5707), the Sceptre uses SMD devices.

The transistors are in a package equivalent to a Sanyo PCP

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The transistors have identification that looks somethng like this:

DK o_ QH

I suspect that these markings identify the manufacturer, the manufacturer's code for the particular component, and possibly a date code. Needless to say, none of the SMD identification lists show a device using either of these codes in a similar package. I started with Sanyo because they make the transistors used in the Dell monitors mentioned above. Unfortunately, while Sanyo DOES use the DK code on their PCP package, the datadheet indicates this is a recent addition to their product line; this monitor was built in 2005.

Using the 2SC5707 I have been able to make an approximate determination of the characteristics I am looking for, but searches are handicapped by the myriad packages used by various manufacturers.

Any suggestions would be much appreciated.

PlainBill

Reply to
PlainBill47
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On Thu, 24 Sep 2009 11:32:39 -0700, snipped-for-privacy@yahoo.com put finger to keyboard and composed:

Sanyo PCP1201:

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- Franc Zabkar

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Please remove one \'i\' from my address when replying by email.
Reply to
Franc Zabkar

Frank,

Thanks, I'd already found that information. There are reasons to believe that is not the proper part.

  1. The power supply / inverter circuit board has a 12/01/2003 date on it; the monitor was built in May, 2005. Sanyo indicates the PCP1201 has a status of 'New'.

  1. AFTER posting this appeal I found pictures of two inverters from Compaq TFT5010 monitors. These use the identical circuit (but a different layout). One of the inverters has 4 transistors labeled DK QH. The other has 4 transistors labeled DK QG. My initial conclusion was the QG / QH is a date code. The QG is used on the same package for the 2SC6096

Wahoo!!! The package is SOT89. Mouser Electronics' search engine shows tiny pictures of the components that match your parameters. I found a PBSS4480X is available in the proper package and appears to have (superficially) the proper specs. Now to see if the package markings match.

Thanks,

PlainBill

Reply to
PlainBill47

On Fri, 25 Sep 2009 11:00:15 -0700, snipped-for-privacy@yahoo.com put finger to keyboard and composed:

It could be a Sanyo 2SD1628:

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- Franc Zabkar

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Please remove one \'i\' from my address when replying by email.
Reply to
Franc Zabkar

Franc,

That seems VERY likely. Thank you very much!!! This is turning into a great day!!!

Replace spark plugs in Wife's van (saving $150 over the dealer's price)

Minnesota beats Northwestern 35 - 24

Find the correct replacement part to repair a monitor.

Thank you very much

PlainBill

Reply to
PlainBill47

Frank,

Well, another problem has raised it's ugly head, and I've finally firmly established the source of these transistors. The Sanyo part you tentatively identified was unavailable from my US sources. After some research, I decided a dxt3150-13 would be an acc3eptable substitute, so I ordered some. Since the original caps in the monitor were Elite brand (a known 'bad' manufacturer), I ordered replacements for them from the same distributor. Before placing the order, I established the monitor would behave in the expected way with the shorted transistors removed. I also tested the transformer to ensure it was not defective.

With the shorted transistors installed, the screen would flash dimly for a few seconds, then go blank. After they were removed, the screen would come on for a few seconds, then blank. (This is the normal result of the protection circuits shutting down the inverter because of insuffficient output). When the replacements arrived, I soldered in the new transistors and tested it. It worked perfectly for a few minutes, so I shut it down and began to replace the questionable caps.

After recapping, the intermittent dim flashes returned!!! However, neither the original nor the replacement transistors are shorted. It is a puzzlement; I'll be using a scope to see if I can figure out the problem.

In the meantime, I had received a Viewsonic VX910 monitor. The owner indicated it was having difficulty turning on, but would eventually start. Rather than try to verify this, I simply opened up the monitor, and found three obviously bad caps. These were Capxon, also notorious for premature failures. And while I was at it, I replaced a fourth Capxon capacitor, in the inverter circuit. When I turned it on, it gave the smae symptoms as the Sceptre monitor. And the transistors were not shorted.

Researching the Viewsonic, I found it was sold in Germany as a Belinea, and a complete service manual (including schematic and parts list) was available for download. What's more, both the Sceptre and Viewsonic used the same design for the inverter!! Browsing the parts list, it turns out the transistor in question is a Rohm 2SC4672. DK is the part identifier, Q indicates the gain range, and K appears to be some sort of production or date code.

PlainBill

Reply to
PlainBill47

There is a tenedency to say that because two events (no display on two monitors) occured after a pair of similar events (replacing the caps on the power supply / inverter boards for the monitors), there must be a common cause. Well, there was, but it was biological in nature, not electronic. The scientific term would be 'incompetent technician'.

On the Sceptre monitor, reseating the connections for the CCFLs solved the problem. It is currently undergoing a 'burn in' phase prior to being reassembled.

On the Viewsonic monitor, testing the transistors showed that a pair of them are shorted. And since there were none of the characteristic probe marks on them, the logical conclusoin is that I INTENDED to test them, but neglected to.

PlainBill

Reply to
PlainBill47

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