Recent Posts

1

Beginners / Re: Checking for noise in resistors

« Last post by Calambres on Today at 06:42:39 am »

From the era of tube gear, many signal tracers have a "NOISE" mode switch built-in. Example Heathkit IT-12.
That applies high voltage bias to the probe about 115VDC/1.7mA and with the audio amplifier you can listen to the result.
A noisy resistor or capacitor with bad dielectric can be flushed out. It was a common problem in the day.

Yeah, that's the Heathkit unit I talked about in a previous post in this thread. It is unobtainium here in Europe at least at a reasonable price.
That was more or less the circuit I was trying to make, albeit somewhat modernized, i.e.: no tubes 

2

Test Equipment / Re: new killer scope in town - a true game changer from R&S - RTB2002 & RTB2004

« Last post by electronix27 on Today at 06:41:09 am »

@ Rydda

Thanks for the very detailed and informative post.  At least I now know someone else has experienced this.

Russell

3

Microcontrollers / Re: SD Card reliability in SPI mode

« Last post by betocool on Today at 06:40:23 am »

The card is not physically damaged, and yes, on one occasion a Windows format fixed the 'reading directory' issue. I haven't tried formatting the card using FatFS, that functionality is not yet implemented in the micro. Another thing I could try to "fix" the card. Not something I'm keen on before getting the data.

Cheers,

Alberto

4

Repair / Re: Tektronix SC502 Alt and Chop mode fault

« Last post by BlownUpCapacitor on Today at 06:39:40 am »

AHH DAMMIT. I SHORTED U360 WITH THE GROUNDING SLEVE AT THE END OF MY OSCILLOSCOPE PROBE TIP WHILE I WAS PROBING AROUND. THE WHOLE ERROR CHANGED NOW.

I guess I'll go purchase some new 7472 chips. These seem are though as the ones on digikey are SMD, and the ones on Ebay are expensive. Good bye money!

New symptoms: CH1 mode works just fine and dandy. CH2 mode works well, but the trace gets dimmer when in that mode. Alt mode shows only CH1 with a dim trace, same with chop and CH1-CH2.

5

Repair / Re: Tektronix 2225 vertical display problem

« Last post by BlownUpCapacitor on Today at 06:37:17 am »

Possibly a burnt input resistor. Some other guy somewhere here had a burnt input resistor on a 22xx series scope. It's soldered directly on the BNC so not hard to check.

6

Beginners / Re: Is this 220v capable board? (Dewalt DCB095)

« Last post by soldar on Today at 06:36:16 am »

I have a Ryobi drill and charger bought in the USA. The charger says 120 V and it definitely is only for 120 V. I used to use it with a stepdown transformer but one day, I do not know what I was thinking, I plugged into 230 V and it promptly blew the filter cap. After replacing it the charger worked again. At 120 V, of course.

You would think they would make the chargers good for 120 and 230 V but they don't and they make separate adapters. My guess is the do this to maintain separation of markets. In the USA the products are cheaper than in Europe and they try to put obstacles to private or grey market exports.

I am guessing this is what Dewalt tries to do too. Even though the unit is good for 230 V they try to scare you into thinking it is not.

7

Repair / Tektronix SC502 Alt and Chop mode fault

« Last post by BlownUpCapacitor on Today at 06:35:50 am »

Hi, I have an SC502 that I broke while trying to fix it.

I was initially trying to remove the mode select cam to clean it because it was full of gunk, but I ended up bending the golden contacts and had to disassemble the entire scope to fix it.

It appears that disassembling the scope and fixing the gold fingers has introduced a new problem. Alt and Chop modes on my SC502 no longer work properly.

Alt has a fault where the trace times are not 50% split, but rather split randomly. Video here: https://youtu.be/vQjHu17QHKY The switching waveform is what you'd expect. Sometimes it's high, sometimes it's low. The effect is not very noticeable at higher sweep speeds.

Chop mode is more strange though. There seems to be ringing? Some kind of distortion in the chop signal. The oscillation signal by itself seems fine. I'll include some images.

Not quite sure what happened. I've ruled out the cam switches. Maybe I damaged the chips with ESD while disassembling it? I work in my bedroom so it is possible.

8

Beginners / Re: Automatic golf ball dispenser

« Last post by BTO on Today at 06:35:17 am »

Ok so I simple need to power sources

Hey, i can see you're pumped about this.  I'm curious, once you work out the bugs, what do you plan to do ?
is it gonna be a one-off where you use it for yourself or are you planning to make a business of this and sell a few of them.
I reckon you should do the latter

Just another point of view (as a 50 year old who's been in business for 35 years).
Electronics is cool and all but if you can design stuff then sell it, You get make money and have fun.
in your case, You get to make money, have fun and play golf

so, what was your plan here ?

9

Projects, Designs, and Technical Stuff / Re: Heated Ferrite == Useless Ferrite

« Last post by moffy on Today at 06:35:06 am »

An interesting discussion, but I haven't seen @GelatinCapacitor how the cores have failed. Do they have reduced permeability or saturation? Some quantitive measurements would be of interest and might point to a possible cause.

10

Beginners / Re: LC filtering for combined Vref/VDD of ADC

« Last post by pcprogrammer on Today at 06:30:49 am »

Better way of doing this kind of thing is to create separate supplies for both analog and digital. Can be done with ferrite beads, resistors and capacitors coming of of the same supply voltage. By matching the supply voltage of both the digital and analog parts by trimming the series resistors there is little risk in exceeding maximum input voltages. The ADC works down to 2.7V and most likely the MCU you are using will also allow for some deviation of the supply voltage.

Also using multiple different value capacitors in the decoupling helps in reducing the noise. A friend of mine who is much more of an expert advised me to use parallel 100nF, 10nF and 1nF capacitors before and after the ferrite bead, and then the series resistor followed by a larger capacitor like 10uF. Then still add the 100nF decoupling capacitor advised for most IC's. See page 18 of the MCP3202 datasheet.

The different value capacitors seem to have different responses at different frequencies and therefore do a better job in filtering a wider spectrum, so I'm told.