Recent Posts

1

Repair / Re: HP54600B with spike problem with and without signal

« Last post by iMo on Today at 07:35:29 am »

First tell us what are the voltages of your signals, it should be 5V aprox. Next pls indicate the name of the pins, leke D4, /WR, /RD, /CS, /OE, A11 for example.
The ramp on your last shot is suspicious. The U33 memory is 85ns access time, afaik, so you should see all sigs well on your 100MHz scope.

2

Test Equipment / Re: Siglent SDS800X HD 12 bit DSO's

« Last post by rf-loop on Today at 07:34:25 am »

Imho, this is a feature.

My understanding of a feature in regards to a program, tool or software:
- Something that helps the user, like informations.
- Seome functionality that speeds up things.
- Some function you can do with a device.

Have not seen the use of the word "feature" for something that is bad  on a device.

Resources might be limited, so this i would consider normal behaviour.

Your language and my language and then foreign language to both... english... dinglish ... and finglish .. and in user manual chinglish but still we mostly undertand... if we want.

By finnish: Ominaisudet
Germany: Eigenschaften
In my english: Features (also Characteristics)

There are bad features and good features.

3

Test Equipment / Re: SDS800X HD Review & Demonstration Thread

« Last post by eTobey on Today at 07:29:34 am »

SDS824X HD Trigger rate

What do the values in the third column mean? I just dont get it. Even after the next day. I only see a proportinal relation to the record length.


I have deleted my off-topic posts in here, and i suggest others to do the same.

4

General Technical Chat / Re: Do you think an LED is a resistor?

« Last post by Someone on Today at 07:26:59 am »

non linear system has linear approximation around a small operating point....

STOP THE PRESSES!

... oh wait, that's the underlying principle of how spice AC analysis works.

Small signal analysis has nothing to do with what we are discussing here.
The resistance I talk about is the static resistance, not the dynamic or incremental resistance of small signal analysis.

Try again.

That was your long winded and dithering proof:

So, we are now seeing the diode as a voltage dependent resistor. Let's see... what is the resistance 400mV? Let's zoom in:

[MASSIVE IMAGE]

I'd say it's about 23.2 kohm.
Let's see what is the resistance at, I don't know, 660 mV (about 5mA of diode current). We can compute it by hand of course, but on the graph we see it is 132 ohm.

[MASSIVE IMAGE]

Now, let's see if we can make something with these values...
[snipping conversational fluff]
Ok, exact same results, if we neglect a bit of rounding error in reading and setting the values.
Now, take your black boxes out of the fridge. Put the diodes D1 and D2, and the resistors R1 and R2 inside a black box each. Shuffle them around. And tell me: without looking inside the black boxes and without resorting to second order effects (like temperature dependence, or changing the other circuital parameters to change the operating points) can you tell me which are the diodes and which are the resistors, by simply measuring voltages, currents and powers?

So to try and claim you're not relying on the well known small signal AC parameters is plainly incorrect.

If you dont like relying on small signal characteristics, perhaps "try again" with your explanation/justification.

5

Test Equipment / Re: Amber model 3500 distortion / noise measuring set manual / service manual

« Last post by oddbits on Today at 07:26:33 am »

yes 3500 , i have 2 , one in fair condition and one in good condition , both have dead battery , one does take power the other does not, so are they worth the hassle and time to try a repair ?, Thinking i may get one good one from the 2 ? , but like i say can not find any info on the web about them.

6

General Technical Chat / Re: Do you think an LED is a resistor?

« Last post by Berni on Today at 07:21:26 am »

Resistor < Linear resistor U Nonlinear resistor
Nonlinear resistor < incandescent lamps U diodes U ...

So, you can still call it a diode, recognize that it is a nonlinear resistor and, as such, that it belongs to the more general set of resistors.

Does this make any sense to you?

It does not make sense.

All resistors exhibit electrical resistance.
All of those semiconductor devices indeed also exhibit electrical resistance.
However not all devices that exhibit electrical resistance are resistors as they are not components purposely designed to implement a well defined resistance.

Does not matter what you understand as "resistor", the vast majority of forum members you are talking to on here understand it as a device specifically designed to implement a well defined amount of resistance. You don't have the authority to redefine established industry words used by others.

What you are trying to say is that a diode exhibits the effect of "electrical resistance" or "resistivity".

This effect is not particularly special and just describes that the device can consume electrical power and turn it into something else,

The point I make is that this is ALL a diode does.
Huge resistance when reverse biased, small resistance when forward biased. This is not a side effect. It is what it does (if we neglect secondary effects due to parasitics in real devices).
It does not store energy in the electric field.
It does not store energy in the magnetic field.
It does not do whatever sorcery a memristor does.
It just oppose a resistance that takes power out of the circuit.

Yes we all agree on here that at some fixed DC operating point a diode acts like resistance.

The point is that a diode is nothing special at doing this. The laws of physics force all power consuming components to look like resistors in steady state DC. This means that at a fixed DC operating point even a memristor is actually just electrical resistance, much like a diode acts as purely electrical resistance at that DC state.

Like what else do you expect an component to do at DC? It can either act as a power source (like a voltage or current source) or it can resist the flow of current hence resistance. There is nothing else for a component to do at DC.

7

General Technical Chat / Re: Do you think an LED is a resistor?

« Last post by SiliconWizard on Today at 07:18:36 am »

That's, once again, just about modeling. You can model all your heart's content, if you find that fun or see any practical use. Ultimately, it's just MODELS.

You're taking an I-V characteristic, basically, and claim that R = U/I, except that R here is a function of U (or I). Which makes it a dubious use of the "resistor" term, as quite a few have already said.
It doesn't serve much purpose either, other than playing with I-V characteristics, which is something that is pretty basic electronics, and obviously useful in itself.

And yes, inductors and capacitors are a slightly different beast, as they involve derivatives and their model is thus a differential equation. But you can still express them in terms of a relationship between U and I; no pun intended.
If you further twist your definition of a resistor with differential terms, then inductors and capacitors also become "resistors" in your definition.

Obviously that's still playing with models, as real-world parts all have resistive, capactive and inductive components as parasitics, and while useful, even the Shockley approximation is ultimately just for the birds, as someone would say.

8

Repair / Re: Acer projector P5530 Model D1P1704

« Last post by MathWizard on Today at 07:18:18 am »

Here's some LED codes from a manual. If this thing is pretty new, you probably won't find a schematic. IDK what voltages the 240W bulb uses, but there's probably not very many voltage rails to check, if it's already running.

From the pic's I'd guess there's a boost stage like to 340V maybe, and then another stage or 2 for driving the lamp.

And the little transformer on the far left might be for 5V standby, or 5/12V for all the circuits outside the PSU. If I had this to work on, I'd make my own schematic in LTSpice, but yeah it takes time.

I'd look up all those chips on the PSU, see if they have Vcc, and if any of them have an ENABLE pin, or a power-good pin. Pretty much all those controller chips will be checking for under-voltage/over-voltge, over-current, and might be shutting down.

There could be some power problem on the other boards, you can check for shorts on some other boards. And there could be a logic signal coming back to the PSU saying to not drive the light.

If I knew the low voltage rails to the rest of the machine, I'd even try powering that from some modem or cablebox PSU, or benchPSU if you have one, just to measure the current draw.

https://global-download.acer.com/GDFiles/Document/User%20Manual/User%20Manual_Acer_1.0_A_A.pdf?acerid=636595271962374228

9

Test Equipment / Re: Lecroy Wavesurfer 44MX vs WS3054

« Last post by alm on Today at 07:18:11 am »

I haven't used either scopes, but from this thread it sounds like the WS3000 series might be a bit under-powered with simpler software than the full Windows-based MAUI scopes: https://www.eevblog.com/forum/testgear/lecroy-wavesurfer-3054/

The Wavesurfer 44MX is a full Windows scope that will likely perform better, although it sounds like its power supply is not the most reliable.

10

Beginners / Help Identifying an SMD component

« Last post by Jterlato on Today at 07:17:19 am »

Hi All I'm new here. Long time lurker, first time poster.

Hoping someone could help me identifying the below SMD component that I need to replace in a USB keyboard (music). Its been knocked off the board by the back of a USB B port which came apart when the keyboard was dropped with the USB cable connected.

Looks like its involved in a USB power circuit. I'm having trouble identifying it based on its markings, and i cant test it as its been destroyed. Any ideas?