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**Shotgun25** · 03-07-2017, 08:21 AM

Re: Dell E197FPf no power on and squealing transformer - guidance?

Forgot to mention that those two blue wires are to a fuse 250v 3amp fuse until I have repaired the circuit, I'm not buying the 250v 3.15amp radial fuse. This squeal was present before the fuse blew.

I have measured U851 (1506 0631cl) as follows

Pin 1 - 12.10v
Pin 2 - 5.14v
Pin 3 - 0v (GROUND)
Pin 4 - 1.24v
Pin 5 - 0v

U850 is SG5841JSZ

I have a SG5841SZ (not SG5841JSZ) I can buy from eBay and looking for datasheets, these seem to be the same part, but unsure if they have different use/operating modes based on that J letter. The datasheets are identical.

I started this project about 2 years ago replacing the caps, and didn't know what to do so put it back in storage up in the attic.

Could someone give me a starting point please?

I have watched quite a few videos on SMPS troubleshooting and I think everything upto the filter capacitor is fine, and from other threads on this forum I think that the transistor and U850 might be fine, but I am not an expert so I'm unsure where to go from here.

**piernov** · 03-07-2017, 03:51 PM

Re: Dell E197FPf no power on and squealing transformer - guidance?

I'm not an expert but I would take a look at the 3.3V LDO which is probably U802 (at the left of the main filter cap), I can't read the markings. U801 (just below) may be interesting too.
Given the measurements of U851, 5V & 12V looks ok, but the 1.24V you get for the buttons seems a bit low to me.

**Shotgun25** · 03-07-2017, 04:11 PM

Re: Dell E197FPf no power on and squealing transformer - guidance?

Thanks for the response, I'll check when I'm back from training. Something useful to do with my cool down for sleep hour

**Shotgun25** · 03-08-2017, 05:09 AM

Re: Dell E197FPf no power on and squealing transformer - guidance?

Right I have checked the U801 and U802 and the readings are as follows.

U801
Pin 1 - 0V
Pin 2 - 1.24v
Pin 3 - 5.14v

U802
Pin 1 - 0v
Pin 2 - 0.44v
Pin 3 - 1.24v

What does that mean then?

Has U802 failed or is what is supplying U802 not correct? Do I need to trace before that component or is that the culprit?

Just for good measure, I have checked I851 to the left of the transformer (feedback circuit on primary?).

I851
Pin 1 (R) - 2.48v
Pin 2 - 0v
Pin 3 (K) - 8.93v

**piernov** · 03-08-2017, 11:52 AM

Re: Dell E197FPf no power on and squealing transformer - guidance?

Were you able to read the markings on U801 ?
I guess it's supposed to output 3.3V (instead of 1.24V) but I'm not sure.
Check resistance between U801 pin 2 and ground.

I think that U801 pin 2 feeds U802 pin 3, and U802 is supposed to output a lower voltage (2.5V maybe?) on its pin 2.
The issue is probably either U801 itself or a component connected to its output (pin 2).

**Shotgun25** · 03-09-2017, 06:04 AM

Re: Dell E197FPf no power on and squealing transformer - guidance?

U801 markings

Code:

A1
AS1117R-33
B0629 33

Measurements as follows-

Resistance GND to U801 pin 2 - 0.018Mohm after about 30-45 seconds of holding the probes (capacitor charging effect?).
On diode mode I get 834-836 fluctuating.
I measured the pin on the device, not the pad that it is not attached to although I have just measured the pad and it has the same 0.018Mohm resistance.

U801 pin 2 (centre pin?) is not attached to the board, it's a stubby pin for measuring internal stuff I guess, but it's not long enough to reach the board and is not connected.

Should I measure the other pins?

Should I remove U801 or U802 from the board to see what changes (if any) there are to the voltage readings?

**piernov** · 03-09-2017, 03:19 PM

Re: Dell E197FPf no power on and squealing transformer - guidance?

Ok so U801 is indeed a 3.3V LDO regulator. pin 2 is probably connected to the tab and should be the output.
Since it's not outputting 3.3V, either it is dead or the output capacitor is not working properly. You'll need to use your multimeter in continuity mode to know which capacitor(s) is connected on it's output. Then if you have an ESR meter you can check the capacitor, otherwise replace it. If replacing it doesn't work (and you still get the same voltage), you'll have to replace U801.

**Shotgun25** · 03-10-2017, 02:48 AM

Re: Dell E197FPf no power on and squealing transformer - guidance?

Thanks for continuing with this project piernov, it's appreciated you taking the time to troubleshoot my problem and explain things so that I can learn.

I have an ESR meter, so will check the caps, but if it's an electrolytic, I replaced all except the large filter cap with Rubycon low ESR caps a year or two ago when I first looked at the monitor. I'm suspecting the U801 must be bad then.

Looks like the surface mount C807 is directly after the tab using continuity mode. ESR reading is between 0.02ohms and 0.04ohms which I believe is low enough?

I'm guessing that I'd better remove it from the board to test capacitance as it has surrounding capacitors? the reading ranges from 153.4uF to 198.4uF, even though the two electrolytics C806 and C807 are labelled 25v47 (see page 2 top right table https://cdn.badcaps-static.com/pdfs/...3bb75aa682.pdf).

Below is the one time reading of all three capacitors one after the other with maybe 10 seconds between typing the results and placing probes.

C806 Rubycon ZLG 25v47

Code:

In circuit
Rating 181.4mf
ESR 0.04ohm

Code:

Out of circuit
Rating 46.46
ESR 0.10ohm

C807 Rubycon ZLG 25v47

Code:

In circuit
Rating 153.7uf
ESR 0.04ohm

Code:

Out of circuit
Rating 46.61uF
ESR 0.10ohm

C808 SMD unknown value

Code:

In circuit
Rating 182.8uf
ESR 0.04ohm

Code:

Out of circuit
Rating 184.3uF
ESR 0.06ohm

I think we are looking at U801 replacement with those values?

**piernov** · 03-10-2017, 08:34 AM

Re: Dell E197FPf no power on and squealing transformer - guidance?

Except C808 capacitance (you may have written 184uF instead of 184nF), capacitors look fine so I guess you'll have to replace U801. I think a LM1117 or AMS1117 would work instead of a AS1117R if you've got one of those. (3.3V obviously)

**Shotgun25** · 03-11-2017, 09:41 AM

Re: Dell E197FPf no power on and squealing transformer - guidance?

Hi, sorry I was busy all evening so couldn't respond.

I have a lot of failed ATX PSUs, would I find this part on an ATX PSU? I would assume there would be something like this for a PSU that had a proper SATA power connector?

**piernov** · 03-11-2017, 12:43 PM

Re: Dell E197FPf no power on and squealing transformer - guidance?

You probably won't find this on an ATX PSU since the 3.3V line of this kind of PSU provides much more power. You may find it on motherboards (5V standby to 3V standby regulator) or some other electronic devices (LCD display, AV receivers, etc…).

**Shotgun25** · 03-12-2017, 02:18 PM

Re: Dell E197FPf no power on and squealing transformer - guidance?

Hi piernov,

I found a L1117SG on a motherboard, but the motherboard might be working so I'm not likely to take it...just wondering if the part number if found on another board was the right one?

Also just remembered your comment about C808, what am I checking for?

**piernov** · 03-12-2017, 02:47 PM

Re: Dell E197FPf no power on and squealing transformer - guidance?

If it is an L1117SG-3.3 it should work too.

About C808, an MLCC capacitor shouldn't have such a high capacitance (hundreds of microfarads), it is at most about a dozen or two microfarads. When in parallel of electrolytic capacitors, it is often in the hundreds of nanofarads (0.1uF for example).

**Shotgun25** · 03-14-2017, 03:37 AM

Re: Dell E197FPf no power on and squealing transformer - guidance?

Oh, I'll recheck that C808 tonight if I get time.

The L1117SG full printed text is

Code:

L11117SG
QHF1N0104

I found another with the following labeling

Code:

ME1117
A B840

Maybe this datasheet is the correct one for the part I found, not sure but it shows for the BXXX (Page 5) a max output voltage of 2.525v with a dropout voltage of 1.4v max. Does that sound similar? Doesn't mention 3.3, but I think the input voltage is 5v.

I'm not sure if U801 should be similar to U802 or needs to be higher...like you said -33 (3.3v).
If I can't find anything on another board then I'll be looking to order one from Amazon (1x TS1117CW-3.3?) or eBay (10x AS1117R 3.3), unless you have any UK sources that are reasonable prices, or if the ones I found are no good, if you know of any more boards I could salvage this part from?

**piernov** · 03-14-2017, 04:07 AM

Re: Dell E197FPf no power on and squealing transformer - guidance?

You need to replace U801 (AS1117R-33) by another 3.3V LDO regulator so any 3.3V >1A LDO with the same pinout will work. However I'm pretty sure your ME1117 isn't compatible (either an adjustable or 2.5V fixed regulator). Same for the L11117SG which is probably an adjustable.
For adjustable regulators to output a specific voltage, you need to add a voltage divider (2 resistors) on the ADJ pin between OUT and ground. Sadly I can't tell you the values because I don't know how to calcultate them.

I don't know any specific UK source. But even eBay should be OK, chances to get a dead part are low.

**Shotgun25** · 03-14-2017, 07:16 AM

Re: Dell E197FPf no power on and squealing transformer - guidance?

Thanks for clearing that up. I might try and work out the voltage divider myself then as I don't need 10x AS1117R-33.

I have a HP printer I am planning to tear apart and I already tore apart a brother printer so I'll check those out for now.

Appreciate you sticking with this one, I hope to be able to resolve this soon and prove your hard work worth it.

**Shotgun25** · 03-14-2017, 07:47 AM

Re: Dell E197FPf no power on and squealing transformer - guidance?

I've found this listing on eBay and I am waiting for the seller to give me feedback on compatibility.

http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=131779133332

**Shotgun25** · 03-14-2017, 08:25 AM

Re: Dell E197FPf no power on and squealing transformer - guidance?

Sellers feedback was "ams1117-3.3, I think this probably would be suitable as a quick check betwen datasheets suggests a similar drop out voltage, sams pinout and slightly higher current rating. I can't 100% guarentee it'll work but lets say it's 95%. If it was me, I'd stick it in but I won't 100% guarentee it."

So I have ordered the part in a pack of 5 for £1.49 delivered. Should be with me by 17th March, will update the thread with the outcome.

One question before I end, that regulator has the centre leg, should I solder that or cut it?

**Shotgun25** · 03-17-2017, 05:17 AM

Re: Dell E197FPf no power on and squealing transformer - guidance?

Hi, I'm back.

The part arrived today (AMS1117 3.3v regulator in SOT-223) and I desoldered the suspected part and installed the slightly lower profile part and the unit powered on!
There is a quieter pulsing squeal now from a transformer, but that might not be noticeable once I have the thing back in the case behind the metal chassis.

For information I did solder the centre pin.

Now I need to buy the replacement radial fuse and this thing can be put back together and test it for a few weeks.

Many thanks to piernov for the help

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Dell E197FPf no power on and squealing transformer - guidance?

Dell E197FPf no power on and squealing transformer - guidance?

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