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21
So here is my problem. Opto feedback for the TL494. Really the only issue is how do I choose the values for the components. The original values are for 5Voutput voltage. I need it to work in the range of 400 to about 630V. Or I can just have them a fixed a fixed value and solder the components accordingly for the voltages. I would really appreaciate if someone would rather show me a way how to choose these values instead of just giving me the values,  if someone could tell me what values to use.

My idea was to simply lift the entire FB circuit with a resistor, so instead of grounding it directly I would put a resistor where the ground was originally and lift that entire circuit above ground. I just dont have an idea if that would work, and the most criticall of all is that its best to not load the output but very lightly. Small mA currents in a 5V supply dont matter but 1mA at 500V is HALF A WATT. Not like its a big deal considering the output power of the circuit but its there just generating heat.

Edit- the pics are fixed yes I noticed sorry my mistake
22
Metrology / Re: Ultra Precision Reference LTZ1000
« Last post by Edwin G. Pettis on Today at 08:04:09 am »
Is your Teko case well grounded?  As far as being steel, that is a good first step.  If you are still experiencing excessive noise on your reference output, then the EMI is likely being conducted by the cabling to and/or from the power supply or DVM/scope.  The noise can be coming from the power supply (also conducted through from the power line) or the EMI is being radiated by something nearby.  Since you say that you did not notice these glitches in the previous month then something has changed since, something you added in the room perhaps or something new generating noise on the power line.  Sometimes large appliances such as refrigerators will generate power line hash or transmitters for instance.

The LTZ circuit is incapable of generating such noise itself aside from little 1/f noise spikes so when experiencing unusual noise on the output of the LTZ circuit look for outside sources and do no try to band aid the problem by putting capacitors where they don't belong.

If the spikes are still present on the output of the reference when operating on a battery, you've just eliminated one source, the line operated power supply.  Since you say there was only a 0.14PPM drop in noise then that is mostly just 'normal' noise your power supply is generating, then you need to look for the source of the spikes, start turning things off and seeing if the spikes go away.  What kind of lighting do you have, that is another wideband noise source if it isn't incandescent or Halogen.
23
Yeah, especially when they're posted in succession like that.

The colors of the Hantek are rather Philips-like.
Or of course it could be that the Hantek is much newer and uses advanced chipset so complexity is reduced  :-//

Protek / Hang Chang not Hantek ;)

Woops, I didn't even realize that I was auto generating portmanteaus. ;D
24
Thermal Imaging / Re: Troubleshooting Cadillac Camera
« Last post by Bill W on Today at 07:57:21 am »
OK, so a relatively early one.

The ones going through when I visited were edge detected and CD motor for automotive use.  The OEM kits at the time were using the Swiss motors but they could suffer from instability due to gyroscopic effects which we (EEV/Marconi) noticed when making the first Argus 3's, so changed to the CD motor.

A fair chance Argus parts would fit.

Bill
25
Repair / Re: Replacement options for TO-3 package Mosfet?
« Last post by anewmanx on Today at 07:55:17 am »
Edit: bah, nevermind, wrong part number. I thought had found a replacement part that would work on Mouser for a retrofit, but I had the total dissipation number wrong.
26
Readability of the TFT cannot be compared to standard segment (TN) LCDs, even if a backlight is used. Current consumption is considerable, that's true, but as a consequence, most of these meters come factory equipped with a rechargable battery (LiIon / LiPo4 chemistry on the recent ones) and a charger. Of course, it's a little more troublesome to always make sure the battery is charged, but compared to some of the OLED meters with primary batteries or crappy 9V block NiMHs, they are a big improvement. If you've got to work in areas with low ambient lighting and have to read the meter at awkward, varying angles, or you want to record a video clip of the screen, they are really worth a thought. Moreover, the TFTs are quite fast though this may not be of much importance in case of a multimeter.

Cheers.
27
more back story...
it turns out that the built in feeders (push feeders) have a part height limit of 5.6mm and I was told that they were not as dependable as the cartridge feeders. So I would still need a machine with the cartridge (CL) feeders. I selected the VP-2500HP-CL32, and some CL feeders which pushed me to my budget limit. $2000 of it is shipping!
8mm CL feeders ( clones but good ) should cost you about $USD60-$65.     How much did you pay for them.   I am yet to see a push feeder that is relialbe, and will keep working reel after reel of part.  But its a cheap way to make it.

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Additionally I requested from SmallSMT an existing customer contact that I could talk to and get their thoughts on SmallSMT and their machine.
We've been hoping a bonafide customer does come and do a review.  Just still waiting for one.   The only person i know who had  bought a a Jushengtech machine and dealt with Sunny,    had an absolutely terrible result, the machine was virtually unusable.   That was however in a previous incarnation, ( cna't remmber what Sunny used to call her self then ).   

 This went well and the customer was happy with the machine and did not have any major problems. I requested a copy of the manual and a software demo download. They gave me a password to their site download area. The manual is ok. There are a lot of configuration settings! I could not get a copy of the software which is very disappointing, I hope its not shit! I believe the software is protected with a hardware key.

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I'm not sure of the history/ownership of the SmallSMT company but I think Michael is in Germany and handles technical support questions and may have designed parts of the machine???
Follow the money.   It did not make sense back then and it still seems odd now.  Its not a typical chinese setup either.

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Sunny is somewhere in China and it looks like he
"She"

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Stay tuned for more...

I hope this works out well for you.
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Bean, you're just awesome at these. I will have to start calling you Dr. Bean, Test Equipment Podiatrist. :-DD
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Repair / Re: MSO7014B bad encoder
« Last post by bitseeker on Today at 07:44:15 am »
Sounds like a high probability it's going to be an easy clean up. I've done a bunch of them, but not on a scope (yet).
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