What frequency limit I should plan for when choosing oscilloscope for TV repair?

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

i think i would keep the old board and try removing bits one by one to see if there is a negative effect.

make sure your 5v supply has the output side totally isolated from the input & ground btw.

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

Here's how it mounted up in the panel. Not perfect, but about the best I could do with just tin snips. I secured it with a lot of hot glue and it's solid. I also replaced the receptacle because I wanted to add the other 2 screws so it would be more secure. I'll slap some Bondo on it and repaint the whole thing when I'm finished.

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

i think i would keep the old board and try removing bits one by one to see if there is a negative effect.

make sure your 5v supply has the output side totally isolated from the input & ground btw.

It is completely isolated. Is it still ok for the neutral to share J2?

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

I ran a simulation in LTspice with everything removed, a 5Vdc supply added. I tried it with and without the one diode added between neutral and J2. It seems to function the same. I also forgot that I have some small proto boards so I can just make the circuit on one of them and make it fit where I want it.

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

it should be o.k. as long as the neutral is not connected to the input earth or any of the standoff posts through a ceramic cap.

btw, dont you have a dremel-style tool for cutting stuff?
they only cost about $20 on ebay.

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

about proto-boards.
remember with mains you need a decent gap between the tracks to prevent arcing.
so no .1" stripboard!

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

about proto-boards.
remember with mains you need a decent gap between the tracks to prevent arcing.
so no .1" stripboard!

Probably a good thing you told me that before I blew something up.

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

it should be o.k. as long as the neutral is not connected to the input earth or any of the standoff posts through a ceramic cap.

btw, dont you have a dremel-style tool for cutting stuff?
they only cost about $20 on ebay.

I have a cheap Chicago Electric dremel, but it's junk. The battery lasts all of 10 minutes and it has a bad wobble. It won't do any precision cutting. I was just pricing genuine Dremels a couple days ago. I want a really good one with the flex extension. I'll probably get one in a couple weeks.

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

personally i would not buy dremel on principle because of the price.

this is the model i'm used to seeing around, only in europe it has other names on the sticker.
http://www.homedepot.com/p/WEN-Rotar...2305/203604481

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

Probably a good thing you told me that before I blew something up.

you can use stripboard if you completely remove every other strip.

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

btw, you need that diode from the mains for a ground-reference.

why not use the old board and remove d3,d4 and r8?

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

corrected the schem.

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

corrected the schem.

Cool. The bridge rectifier is also a single device. It's marked DB107.

So, I have it going, but it's not reading right. 130V input and it's reading 79v. I've tried with all the components in except for the cap and 33Ω resistor. I'm thinking they've software compensated for the device load or something. It also reads 3-4v with nothing connected. I'm thinking maybe a dummy load to simulate the device load.

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

maybe put the cap & resistor back and lift the 5v wire off the small board.

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

maybe put the cap & resistor back and lift the 5v wire off the small board.

You sir, are a genius!

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

So, it's working now. It doesn't really start measuring until you get to around 4 volts. It reads about 3 when there's no power. Once you get a volt past that, it works but is always 1 volt less than my Fluke. I wish I had a decade resistance box because I bet I could dial it in. So, without that 33Ω resistor, it was way under the correct voltage. I can say that the resistance was higher without it. Adding it reduced the resistance on that part of the circuit and brought the voltage up to within 1 volt. I'm thinking if I reduce the resistance a bit more, it will give me that other volt.

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

I think I've figured out how to make everything fit too. I'm going to eliminate the fuse holder and replace the switch with one which has a 10A circuit breaker built in. Then I'll mount the SMPS and sense board to a piece of proto-board with standoffs, and glue it to the center of the panel with hot glue. Then, all I need is 4 90° bracket to mount the panel back on.

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

4v?
i'm surprised the reostat can go that low without cutting out anyway!

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

With my Fluke, I can read it all the way down to 0.75v.

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

Well, it's on hold until the new switch and stuff gets here. I appreciate all the help. I couldn't have done this wondering now if the magnetic field from the variac is going to affect the ammeter, since it uses an inductive coil. Well, I'll find out when it's done. It's not incredibly important, the voltmeter is what I'll use the most anyway. I wonder if it uses the value of the ammeter for the wattage calculations too?

I found these adhesive backed nylon standoffs to mount everything.

http://www.ebay.com/itm/PCB-Standoff...0AAOSw3ydVro9U