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

[lookimback]

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

I would think that line voltages would have been more prone to fluctuations decades ago when that equipment was in use too.

[lookimback]

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

So, the meters finally arrived. They sent me the wrong one and I got a full refund. I actually like the one they sent me better. It's smaller, but otherwise the same features and ratings. I played with it briefly and found all the ICs to have their numbers sanded off. When I actually get some time, I'll get some good pictures and try to trace out the circuitry. I couldn't identify which pins were for the chip's supply voltage. I did find that they operate fine at 60 to 300v, even though they're rated for 80 to 300v.

[Agent24]

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

Funny how China rips everyone else off, but then often do IC sanding to stop everyone else ripping them off.

A bit of a d*ck move, but I guess it's rather smart actually.

[lookimback]

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

Here's the meter I plan to use and all the pics.

[lookimback]

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

Funny how China rips everyone else off, but then often do IC sanding to stop everyone else ripping them off.

A bit of a d*ck move, but I guess it's rather smart actually.

I agree and it makes me really want to ID these ICs and publish it.

[Agent24]

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

I agree and it makes me really want to ID these ICs and publish it.

Probably doesn't matter, at least one will be a uC and unless you get the firmware what's the point?
Other two are probably just 7400\4000 series for the LED multiplexing

[stj]

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

nice, the small board has 2 pins on the ribbon for current, the other 3 are the supply and sense-voltage.
so just need to draw a schem of the small board.

btw, if you can use a meter to see how the 4pin header on the edge and the crystal connect to the 24pin chip around the ribbon we can id the microcontroller.

[lookimback]

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

Probably doesn't matter, at least one will be a uC and unless you get the firmware what's the point?
Other two are probably just 7400\4000 series for the LED multiplexing

I have programmers. If it's a flash chip, I can read it. I just need the pinout.

[lookimback]

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

nice, the small board has 2 pins on the ribbon for current, the other 3 are the supply and sense-voltage.
so just need to draw a schem of the small board.

btw, if you can use a meter to see how the 4pin header on the edge and the crystal connect to the 24pin chip around the ribbon we can id the microcontroller.

I'll get working on that tomorrow. I'm guessing the microcontroller is the big IC?

This image is from the other one of these. I'm thinking it's probably the same. I played around with Photoshop and made a couple numbers show up.

[stj]

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

no, i think the big ic is the led driver - probably serial input.
i think the microcontroller is the medium-size one near the cable
the givaway is the 4mhz crystal

[lookimback]

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

no, i think the big ic is the led driver - probably serial input.
i think the microcontroller is the medium-size one near the cable
the givaway is the 4mhz crystal

Ah I see, because the microcontroller needs the clock signal.

[stj]

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

exactly, and tracks must be short.

[lookimback]

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

Is this likely to have one those internal fuses that they blow after programming the ROM to prevent it from being dumped?

[Agent24]

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

Is this likely to have one those internal fuses that they blow after programming the ROM to prevent it from being dumped?

Likely, I think most microcontrollers do... the question is, did they use it?

[lookimback]

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

Likely, I think most microcontrollers do... the question is, did they use it?

I guess I'll figure that out after we ID it. I hope they didn't. I'd like to be able to see the code and try to figure it out.

[lookimback]

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

Here's the schematic I made for the small board.

[stj]

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

nice
so J2 is ground AND SHARED WITH THE SENSE INPUT
and J3 is the positive supply

d3 and / or d4 are probably zeners - see what's printed on them.
stuff 100'ish volts into the circuit and put your multimeter across j2&3 - lets see if it's outputting 5v

btw, what's the voltage rating on the electrolytic?

[lookimback]

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

nice
so J2 is ground AND SHARED WITH THE SENSE INPUT
and J3 is the positive supply

d3 and / or d4 are probably zeners - see what's printed on them.
stuff 100'ish volts into the circuit and put your multimeter across j2&3 - lets see if it's outputting 5v

btw, what's the voltage rating on the electrolytic?

The zeners are marked Z5V1. I'm finding datasheets for 5v1 and their the same as a 1N4733. I'm guessing 5.1v.

The electrolytic is 10v.

With 100Vac input, I get 4.8Vdc across J2 and J3.

The display reads 99.2 Vac, and I get exactly 100Vac with my Fluke and my Radio Shack meters. Not perfect, but pretty darn close. I noticed all the resistors are 1% tolerance. I wonder if there's something I can do to make it perfect?

[lookimback]

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

I'm trying to figure how I'm going to mount all of this in the variacs panel. I have the 5v SMPS that I have to fit in there, plus the display, and it's a tight fit already. It looks like most of this board serves to supply the power for the device. Can I just eliminate this board completely by daisy chaining the resistors and connecting neutral direct to J2? Then I could just heat shrink it all. The current sense is completely separate anyway. My thinking is that I don't need If I can do that, I won't need a new panel.

Would this be correct?

[lookimback]

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

Or, is it better with the diode here?