Recent Posts

1

Mechanical & Automation Engineering / Re: Repurposing PVC Pipe for DIY Projects

« Last post by xrunner on Today at 12:02:49 pm »

The builder is using CA glue. What's wrong with what he chose, seems to know what he's doing. You can use SCIGrip 16 if you don't want to use that.

2

Repair / Re: LED Strip lights flashing like a bad 90s rave

« Last post by RoGeorge on Today at 12:01:26 pm »

I would disconnect the LED strip and check the (group of) LEDs individually, one by one, with a DMM or with a voltage source + series resistor + 2 wires.  Could be that one of the many series LEDs is defective (interrupted) and when the voltage across it becomes too high, it short-circuit itself and lights up the rest of the strip, but at a higher voltage than it should, then the overcurrent protection turns all off, and the flicker repeats just as the defective LED would be the starter in a fluorescent tube lamp.

If not, then maybe check for dried out electrolytic capacitors in the power supply (though, they all look OK in the picture).

3

Beginners / Re: Question about use of Differential using scope USB port

« Last post by watchmaker on Today at 11:58:46 am »

Perhaps you are right.  I assumed (never a good thing, especially here) that people looking at Differential Probes have researched good practices, earthing and isolation transformers.  At any rate, that is what drove me to consider the expense.  (I grew up with non polarized plugs and isolation transformers).

But yes, since many Differential Probes were battery operated, I am interested in the impact of the use of a USB port on the scope for power.  Especailly given all the attention to the issues regarding working around USB ports.

FWIW, I did check my 120 vac with it, with no ill effects. But......

4

Test Equipment / Re: Firmware update for Gratten ADS1102CAL+ oscilloscope

« Last post by tv84 on Today at 11:56:00 am »

This is the only Atten CAL+ FW I ever saw.

Don't know what version it is.

5

Repair / Help repairing Klipsch KDA amplifier power supply and identifying smd component

« Last post by r2digital on Today at 11:52:41 am »

Hello, I Have a klipsch KDA500 amplifier that has a bad power supply. It turns on after about 10 attempts but im barely getting any voltage on the -13 volt rail. I have compared voltages to a working KDA1000 with the same power supply and this is what i got. Picture with the purple line shows where the trace starts at the yellow wire and ends at the negative trace of capacitor 35v 47U capacitor and should be -13-14VDC


kda500 power supply {not working properly}

right to left

4 pin

brown 8.06
black 7.93
white -0.11
gray -0.10

5 pin

green 30.16
blue 3.29
green 2.58
red/white 3.01
red 1.11

3 pin

yellow -.759 <—— this should be -13-15VDC
light blue -0.024
yellow 13.78


3 pin

black 165

brown -166

red -165


Kda1000 operating normally

4 pin

brown 8.52
black 8.92
white -0.003
gray - 0.003

5 pin

green 32
blue 3.33
green 2.6
red/white 3.05
red 1.1

3 pin

yellow -13.7
light blue 0
yellow 13.8

3 pin

black 157.5
brown -157.8
red -157.8

55bz<—- need help identifying what this is as it is not giving me proper voltages

these are the measurements from the working power supply on the 55BZ smd component

1 -18.2
2 -18.2
3 -5.83
4 -18.71
5 -18.71
6 -18.71


The measurements from the non working power supply 55BZ chip

1 0.380
2 0.380
3 -20
4 0.420
5 0.400
6 -20

6

Microcontrollers / Re: Divide clock by 3 on a ATF16V8B

« Last post by RoGeorge on Today at 11:47:36 am »

Does it has to be with a PLD?

For relatively constant Fin, a divider by 3 can be implemented with a HC74 D-type flip-flop and an LC, like this:



Found this unusual dividers idea from a PDF by Charles Wenzel, where a tuned LC is inserted in a typical D-type FF divider by 2, so to make it divide with ratios other than 2. 

Tried that once, to divide by 3 a 4.9152MHz TTL oscillator.  It worked very well, stable and not picky to the exact LC values (as long as the LC values are not totally off).

7

Beginners / Re: Comparator circuit seems to be oscillating (well, pulsing, really). Solutions?

« Last post by T3sl4co1l on Today at 11:45:36 am »

Hi

I need your help.

I have checked the capacitors on my digital piano and got the following results in ESR levels. I used the peak ATLAS ESR70 gold.

10000 uF 25V - ESR 0.01
2200 uF 25V - ESR 0.02
470 uF 10V - ESR 0.20
100 uF 25V - ESR 0.43
47 uF 16V - ESR 0.64
10 uF 16V - ESR 1.01
1 uF 50V - ESR 1.10

I am especially suspicious about ther results for 10 micro and 1 micro F. They should be around 8 and 5 respectively. Do these results mean that I need to change the 10 micro and 1 micro D capacitors?

Thanks for your replies.
Tan

Please start a new thread; this bears no relation to the topic above.

8

Dodgy Technology / Re: 10ah 18650 cells

« Last post by Kean on Today at 11:42:43 am »

I bought 48 pcs of HG2 18650 from an AliExpress seller that were specified for 3000mAh down to 2.5V.
I've only been test discharging them so far at 1A to 3.0V, and have been getting pretty consistent readings of 1800mAh.

So not great, but certainly not as bad as some reports I've seen - and for the price I paid compared to local trustworthy suppliers I am happy.
I will be assembling these into packs that go inside some 12V SLA shells for backup power application.

Some of my other purchases of 18650 cells and packs in December/January never arrived, but AE did process refunds on those.

9

Beginners / Re: Why are thermal jumpers so expensive?

« Last post by T3sl4co1l on Today at 11:41:35 am »

Mind, Al2O3 isn't bad, it's just not as good as metal (or AlN or BeO, lol).  That's still good enough for a lot of things.

You can get ceramic (I think more generic porcelain) heatsinks, it might not be great but it's better than air, and might be used to just take a few to tens of degrees off an IC or whatever.  There were also... maybe they're still available somewhere, but someone made extruded/HIP Al2O3 heatsinks.  ... Aha, here they were: https://www.ohmite.com/wc-series-heatsink/ also CA series (now discontinued?), and also Wakefield CE-OMNI-38, so I guess there is one surviving [equivalent] line across two mfgs (or maybe they're both from a common source and selling as brands, who knows).

Main thing is, plopping hunks of ceramic around a design isn't going to do much unless there's good thermal contact between everything.  An SMT chip can't be very big to still be a chip, which makes AlN great for it, and the solder is good thermal contact.  Al2O3 is good, but not great, and the low aspect ratio of a chip hurts more; it would have to be more cubic to do a comparable job.

Or insulator plates and such, but they have to be fairly thick for strength, which somewhat defeats the purpose.  Not to mention the plates themselves might not be very smooth, and heatsinks are rarely very planar, so you still need a generous dose of grease to fill everything in.

I suppose a potting compound filled with Al2O3 sand would be pretty effective (not to mention, torture to excavate ).  A lot of thermal potting compounds are basically that, or ZnO or other ceramics, and they do pretty well overall.

Tim

10

Power/Renewable Energy/EV's / Re: Why are all Vicor PI3 modules suddenly out of stock or obsolete?

« Last post by Faringdon on Today at 11:34:34 am »

You have contacted your local Apps Guy from VicorPower?.
I find with Vicor you need to do that.