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Identifying a SMT regulator (long)

I recently picked up a dead Memorex MLT1912 TV (19" Hi definition with LCD display). It was represented as 'dead', and that's no lie!

Investigation revealed the standby LED was on, and no response to either the remote or the control panel power button. This TV get power from a 12V 'power brick'. This appears to be working properly. Further regulation used N2596G switching regulators. Some had been turned off via the control input, and determining the resaon was getting tedious, so I switched to 'eye-tech' mode.

That revealed a suspicious burn mark on a connector on a daughter board. Examining the adjacent IC through a magnifier I was able to clearly see that the 'magic smoke' had escaped. So far, my attempts to fully identify the IC have been fruitless. A quick summary of what I have found:

SOT23-5 package marked with A17d (the d represents my best guess). Pin 4 is shorted to pin 3. A tentative identification of the pinout is:

1 Control? (CN3-4 via 4.7K R87) 2 Ground 3 Power out 4 Power in 5 Feedback? (Resistor network?)

There is a SMT ferrite bead in the trace to pin 4, and another after the inductor connected to pin 3. It was suggested this is probably a high frequency buck regulator, similar to an Anpec APW7101. Datasheet at

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NOW the problem. Many manufacturers produce buck regulators in the SOT23-5 package. Usually they will have several versions with a fixed output voltage and one with a variable output voltage. All attempts to identify one with a part number including A17? have failed; the logical conclusion is this is a 'device marking', meaningful only if the manufacturer is known. And I have been unable to find any manufacturer using A17x as a device marking - but I'm still looking.

I tried to 'reverse engineer' this by tracing the output. This has also been unsuccessful. I have identified several capacitors that are filtering the output, but cannot find a connection to any IC on the board - but I'm still looking. This is complicated by the fact that this seems to be a multilayer circuit board.

Unfortunately, one of the ICs is a R8A66950BG. Since this is a ball grid package, I can't probe the pins. I have been unable to locate a data sheet, tech briefs indicate it requires 3.3, 1.25, and possibly

2.5 volts - the manufacturer is ambiguous about this.

I have been in contact with Memorex, they refered me to Fox International. Fox International does not list a service manual for this TV. They are 'researching', and 'will get back to me'.

While I'm not out of options, I'm hoping for new ideas on troubleshooting this. Of course, someone correctly identifying the part would be most welcome. Ideas on how to SAFELY determine the proper voltage would also be helpful. Or an exhaustive database of SMT markings vrs part numbers would be most appreciated.

Pictures of the circuit board and the IC are available at

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Thanks,

PlainBill

Reply to
PlainBill
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On 4/14/2009 3:20 PM PlainBill spake thus:

It's experiences like these that lead me to conclude that, more and more, the entire set is to be considered one big FRU.

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Reply to
David Nebenzahl

On Tue, 14 Apr 2009 15:20:17 -0700, PlainBill put finger to keyboard and composed:

Can you apply the voltage formula in the APW7101 datasheet using the measured values of your feedback resistors?

Vout = 0.6 x (1 + Rf1 / Rf2)

You may arrive at a voltage which makes sense as a Vdd for one or more of the chips. Other regulators may use a 1.25V internal reference instead of 0.6V.

AIUI, 1.2V is required for the CPU core, 3.3V for I/O (analogue), and

2.5V for the DDR-SDRAM interface:

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According to the technical brief, "the R8A66950BG requires only the addition of a single 16-bit-width 256-Mbit DDR333 in order to implement various kinds of processing supporting digital TV broadcasting".

It seems to me that there should be a discrete SDRAM chip which will allow you to confirm whether your SMPS is a 2.5V regulator. Otherwise I'd measure any feedback resistors for the other two (?) regulators and determine their output voltages that way.

- Franc Zabkar

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Reply to
Franc Zabkar

Here's a TSOT23-5 with the marking A17:

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It's possible the "d" isn't even supposed to be a letter at all?

If this helps you, I'd appreciate it if you took a look at my head- scratcher:

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-JD

Reply to
jdiaz5513

PlainBill Inscribed thus:

Not much point putting pictures on a site where you have to register to see them !

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                        Baron.
Reply to
Baron

On Tue, 14 Apr 2009 15:20:17 -0700, PlainBill put finger to keyboard and composed:

Perhaps a clue as to the marking code, "A17d", may lie on page 3 of this datasheet:

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The "7" could designate the year, 2007, and the "d" may indicate the week, 30, in which case the "A1" would be the important part of the code.

Is this consistent with the date codes on the other chips?

If the input voltage is shorted to the output pin, then I'd be worried about damage to the downstream parts.

FWIW, the following parts lists have the same R8A66950BG chip (p/n

0IMCR02243A). You can actually buy it for $8 !!!

LG Electronics/Zenith DU-27FB34C:

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LG Electronics/Zenith H20J54DT:

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LG Electronics/Zenith H27H49S:

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Unfortunately none of the "power management" ICs look like yours. :-(

Maybe you could track down a compatible chassis by searching for TVs that use the same major parts. Can you identify the panel?

Can you find another TV brand/model that uses the same remote codes as yours? You could take your remote to a store and try it on the display sets, or search the

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web site.

FWIW, the part number for your remote appears to be "HS-Y3719-BLK-320".

If your TV has an FCC ID, then you could possibly obtain schematics here, or at least determine who actually made it:

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- Franc Zabkar

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Reply to
Franc Zabkar

That's why I was asking here. You have given me two ideas which bear investigating. Yes, there is a single Samsung RAM chip. That does provide an avenue to pursue. Frankly, I had not considered the possibility of determining if this was really a adjustable output regulator. I was fixated on it being a fixed output device and never made the leap.

Thank you for two good ideas.

PlainBill

Reply to
PlainBill

There is a very good chance that the last character is not a 'd'. It was partially destroyed when the chip shorted, and could be part of a manufacturer's logo, part of a 4 or an 8, etc. Datasheet databases have excellent search engines and can find matches for partial part numbers. I was unable to find any part number containing 'A17' which was available in a TSO23-5 package. This led to the conclusion that it was not a partial part number, but rather a 'smd part marking'.

I am also trying to get access to a microscope. That might give me more information.

I'd already looked at that thread. Frankly, you are already beyond what I would consider trying. And I'm notorious for NEVER giving up on a repair until I've irretriveably broken it - and sometimes not even then.

PlainBill

Reply to
PlainBill

Agh!!! Sorry about that.

PlainBill

Reply to
PlainBill

Franc,

Thanks again for so much help. The problem with identifying a part by it's top markings is that unless you can determine the manufacturer it can be pretty tedious. (I know I'm preaching to the choir here). Note that AXElite's AX3503 has a top marking that starts with 'G3'. Yes, it is possible that 'A1' is the significant part of the top marking and 7d represents the 30th week of 2007.

Much of my recent effort has been spent perusing the data sheets of various voltage regulatrors available in the SOT23-5 package, looking for top markings beginning with the latter A. So far this has not yielded any results.

Yes, I am very much aware that the shorted power regulator could have blown the chip it was powering. I'm willing to take a chance on buying a $2.00 part (or two or three of them) just to see if that will solve the problem. I'm a little less certain about trying to replace the R8A66950BG. SMD fuses and resistors don't present a challange. I've replaced a few 16 and 24 pin chips. Ball grid? Well, maybe.

The FCC ID is another avenue I had never considered. Unfortunately, I can't see an FCC ID on it!!!

Thanks for the help.

PlainBill

Reply to
PlainBill

On Wed, 15 Apr 2009 14:50:34 -0700, PlainBill put finger to keyboard and composed:

One other thing I've done when tracking down manufacturers is to look for similar user manuals. Sometimes an OEM will take the easy way out and regurgitate the original Chinese docs. A search for distinctive phrases or typos can sometimes yield results. Adding "filetype:pdf" to Google's search box can narrow down your results.

I've also tracked down the manufacturer of my supermarket DVD recorder via markings and labels on the PCB artwork, and I've even managed to find a service manual from yet another source.

Yet another trick may be to hook up the TV's VGA input to a Windows PC. Windows PnP will then interrogate the monitor/TV. Search the registry for EDID information, or use a utility to display this information directly.

Here's an EDID utility for Windows 95/98/Me:

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Another more sophisticated program is PowerStrip:

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The EDID bytes may include text strings identifying the manufacturer or the OEM or the model.

- Franc Zabkar

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Reply to
Franc Zabkar

On Thu, 16 Apr 2009 18:01:07 +1000, Franc Zabkar put finger to keyboard and composed:

The monitor does not need to be powered up for this to work. This is because the PC's graphics card provides the +5V power for the monitor's EDID EEPROM.

- Franc Zabkar

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Reply to
Franc Zabkar

I finally got back to this briefly yesterday and found that rf1 apears to equal rf2 (each 300K) before being interrupted. I'm going to hone my technique before drawing conclusions; there seems to be a transistor (ID H1A) in the circuit.

I haven't had a chance to trace the output further.

Fox International got back to me; no service manual is available. When time permits I'll be checking if U11 or the entire daughter board is available.

PlainBill

Reply to
PlainBill

On Mon, 20 Apr 2009 09:26:16 -0700, PlainBill put finger to keyboard and composed:

1.2V (= 0.6 x 2) does make sense as a CPU core voltage, and 2.5V (= 1.25 x 2) could supply the SDRAM.

- Franc Zabkar

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Reply to
Franc Zabkar

Yeah, I caught the irony of that. I'm hoping to spring some more time free to probe the source of the 2.5V for the DDRam chip. Working on both sides of a multilayer board is a bitch. It would be easier if I could figure out which of a couple of dozen boxes holds my 30 ga insulated wire.

PlainBill

Reply to
PlainBill

I decided to give Fox Int'l another try and received both good and bad news. Contrary to my earlier information, the service manual is available. Unfortunately, it is not in stock. They list three parts for this set - the main board, the tuner board, and the 'crystal' (Liquid crystal display?) . The tuner board (TL ATSC LCD board?) is listed, and costs only $22. But 'it's out of stock for 2 to 12 weeks'

PlainBill

Reply to
PlainBill

On Wed, 22 Apr 2009 13:53:11 -0700, PlainBill put finger to keyboard and composed:

Hmmm. Fox are the service agents for Memorex, yet neither they nor Memorex have a service manual for a TV that was sold on the US market possibly within the last few years. A service manual would most likely be provided in digital form as a PDF file, so why the delay? Surely it's just a matter of emailing you a copy, or burning a CD-R?

If you intend to sell 10,000 TV sets, say, to a particular market, then surely you will prepare yourself with a service manual and other support materials. What goes on inside these companies? Are their directors really just a bunch of ignorant, incompetent sales droids?

- Franc Zabkar

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Reply to
Franc Zabkar

I've done business with Fox for decades, and have always had satisfactory service. Still, I prefer dealing locally. at least you can see the item before buying it.

There does seem to be multiple levels of incompetence here. Not having service information and parts available, not identifying the availability to a customer, not having the parts in stock.

That brings something else to mind. At one time a manufacturer had to keep parts available for a certain length of time after production ceased - 5 years IIRC. Is that no longer the case?

PlainBill

Reply to
PlainBill

On Thu, 23 Apr 2009 11:14:28 -0700, PlainBill put finger to keyboard and composed:

This requirement is easily circumvented by offering spare parts as modules, and then pricing them so that repairs become uneconomical.

- Franc Zabkar

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Reply to
Franc Zabkar

Well, I'm tentatively reporting success. Focusing on the K4D551638H-LC50 RAM, I was able to determine it got power from U8 a UTC1117. THAT turned out to be a 3.3V regulator. WTF??? The K4D551638H-LC50 requires 2.6 volts! The I discovered that YOUWANG ELECTRONICS makes variants with other output voltages. There are three UTC1117s on the board, the one powering the K4D551638H-LC50 has B25 on it (this is not the date code per the data sheet). The others have B33 (near the Flash memory) and B18 (near the LGDT3303). I haven't been able to find a data sheet for the LGDT3303, but 3.3 volts appears to be right for the flash memory. And all of the UTC1117's were from YOUWANG ELECTRONICS.

The next problem was locating a replacement for the dead chip. My perfered parts supplier is DigiKey. While they list a large number of regulators in the SOT23-5 package, they only stock those from National Semiconductor. And none those have the correct pinout. Bummer!!!

Fortunately, Mouser Electronics came to my rescue. They stock only one adjustable bucking regulator in the SOT23-5 package. It's the Exar SP6669AEK-L, and it has the correct pinout. The best news they will sell in quantities of 1.

Now to make up an order (I need caps, transistors, and a fuse for a dead LCD monitor). Then a weeks wait for the pars to come in. Finally, solder in the regulator and give it the smoke test.

PlainBill

Reply to
PlainBill

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