Sony SDM-S81R Service Manual

[budm]

Re: Sony SDM-S81R Service Manual

I just need the voltage reading of all 3 pins with black lead to the chassis and red lead to each one of those pins.
Also what resistance do you get between middle pin and the chassis ground.

[lcdman]

Re: Sony SDM-S81R Service Manual

Hello Budm,

I'm learning alot on this project. Sorry for not completely understanding before. Ok here we go again, on the outside leg I got 0VDC. The middle leg gave me 2.432VDC. And the last leg gave me 4.83VDC. So now does that give the correct info you were asking for? Does this part need to be replaced with the caps on this board? Where would the best place to get this part?

Thanks Again,
lcdman

[budm]

Re: Sony SDM-S81R Service Manual

That input pin of 4.83 sounds kind of low, I would expect to be 5V, for the output of 2.432V I am not sure if it is 2.5V regulator or lower or higher voltage.
I cannot read the printing on the part, can you see the numbers on it? It seems to be fixed voltage regulator. D6XX does not sound right.

[lcdman]

Re: Sony SDM-S81R Service Manual

Hello Budm,

The numbers on the part are F D3GXX and 1117S25

I'm including a slightly blurred picture I took through my magnifier work bench light. The F is on an angle. Maybe a Fairchild part#? Those little parts are hard to take good pictures of!

Take Care,
lcdman

[budm]

Re: Sony SDM-S81R Service Manual

OK, the 1117S25 is 1117 series LDO, 2.5V, right now it is more than 2% off, and the input voltage also does not look quite right, I have seen this problem before and it was due to bad filter caps for these two regulators. So try replacing the caps first.
I would replace those caps, what I do with the surface mounted is I use through hole cap, cut the legs short and bend the end outward long enough to be able to solder on the old pads.
I would also replace the two large one also, but try the little one first to see if the voltage will come back up.

[lcdman]

Re: Sony SDM-S81R Service Manual

Hello Budm,

So I can replace those polymers with low-esr electrolytics? Is the colored area the negative connection on those caps? If so I'll try them first. I don't have 470uf 25v caps that are short in height so I'd have to order them along with the voltage regulator if it turns out to be shot.

Thanks,
lcdman

[budm]

Re: Sony SDM-S81R Service Manual

Yes, low ESR. The two surface mounted caps, the black band on top is the negative. You can lay the cap side way if you have room.

[tom66]

Re: Sony SDM-S81R Service Manual

For an LDO, it is best NOT to use low-esr capacitors; just a good general purpose cap. ESR 0.5 ohms minimum, 5 ohms max, to ensure stability.

[budm]

Re: Sony SDM-S81R Service Manual

I never run into using low ESR with LDO yet, I check for Oscillation and never senn anything unusual. I use them in our products as well. May be it depends on what kind of load it is being used with. That is why there is a small MLCC with the electrolytics. which I also use in my design.

[tom66]

Re: Sony SDM-S81R Service Manual

Some regulators (particularly CMOS using enhancement-mode PMOSFET pass transistor) are stable with ceramics which have nearly zero ESR. However, the 1117 uses a PNP pass transistor, so ESR is important for control loop stability. See diagram on page 11:



in particular, "Stability"; it appears at room temp the regulator is stable with ESRs from 0.01 ohm (really low) but as it warms up stability problems could become more evident. Output voltage also matters. These things have so many dependencies!

[budm]

Re: Sony SDM-S81R Service Manual

That 117 uses NPN pass transistor setup just like generic design with discrete components (op amp for comparator , ref voltage, etc) that has been around for decades, it just get put in to a small package. Onething is not very clear in the graph is that the stable region, it shows typical <20 Ohms but at the bottom left corner,not sure what they are tying to show, neither it show the graph of other lower ESR before it becomes unstable, Iknow this kind of circuit, too much capacitance at the output can cause Oscillation.
This simple circuits have been around for decades:
http://www.morpheustechnology.com/eX...egulators.html
http://www.ecircuitcenter.com/circui...eg1/opreg1.htm

[tom66]

Re: Sony SDM-S81R Service Manual

I go by what the manufacturer suggests. It appears that in the low ESR region the regulator is unstable by the graph, as well as the high ESR region.

LDOs are often unstable because you have an inverting feedback amplifier, contributing -180deg phase, but then an inverting pass element (i.e. -180deg), giving -360deg overall phase shift. Anything around 360deg is a recipe for oscillations, so the amplifier is compensated (don't ask me how - degree level stuff) but the compensation creates only limited windows of stability.

[budm]

Re: Sony SDM-S81R Service Manual

Yes the feedback is inverted by the op amp to provide less bias to the transistor if the output voltage goes up (or more bias when voltage gose down), but remember, it is Emitter follower circuits (the output voltage will be 0.6V less than the Voltage between Base and Ground due to EB junction voltage), the output at the Emitter is in phase with the Base, no 360Deg invertion. Common Emitter with the Collector output , the signal at the Collector will be 180 Deg out of phase with the Base input signal.

[tom66]

Re: Sony SDM-S81R Service Manual

I'll admit I'm a little out of water here, as I'm not particularly familiar with analysis of these circuits.

[lcdman]

Re: Sony SDM-S81R Service Manual

Hi Budm,Tom66,

So what should I do? Use polys to replace polys and not use low-esr electrolytics? I just want to get my monitor fixed.

Thanks To Both Of You,
lcdman

[budm]

Re: Sony SDM-S81R Service Manual

Those caps (the ones I pointed out) are not polyester, they are electrolytics, if you have general purpose you can use them to see the result.

[budm]

Re: Sony SDM-S81R Service Manual

By the way, if you are not sure about the cap I recommend to use, please see the attachments.
So any more info on the repair progress?

[lcdman]

Re: Sony SDM-S81R Service Manual

Hello Budm,

I put that project on the shelf for now due to not having any (non) low esr caps on hand. I have to still get some to see if that would fix it or not. But when I get some and if it fixes i'll be sure to post an update.

Thanks Again Budm,
lcdman

[budm]

Re: Sony SDM-S81R Service Manual

You can test with regular caps for now.

[capacitate]

Re: Sony SDM-S81R Service Manual

Bumping this because I would like to know if lcdman has accomplished anything? I have the EXACT same problem, Sony SDR-S81R, no orange power led, completely dead. All "Sam Young" capacitors seem fine, no abnormalities in the visual aspect. Will it be a good start to replace all capacitors as well as the 4 found on the "vga board"? Realized that a high percentage of problems lie on capacitors going bad and a very small percentage of them on other components mentioned along the thread. Thanks.