Oscilloscopes

[jboettc208]

Hello!

I am fairly new to the electronics world. Everything I know (Not Much!) I have learned on my own or from books. I have become the go-to guy for friends and family when it comes to fixing TV sets. I do pretty well for only having a couple of DM's. I would like to invest in & learn how to use an Oscilloscope. Could anyone recommend a good starter model that would aid me in troubleshooting TV repairs?

Thanks!

 

[philba]

what's your budget? I don't know TV repair - what's the top frequency you need to see?

I'd suggest you get a used scope. Tek and HP scopes are built like tanks and last forever. Check out ebay.

 

[Sceadwian]

Do you really need an o'scope? Most if not all of the functional parts of a television that are repairable can be tested with a simple frequency meter. Most of the complex waveforms in a TV set are from the image information itself. If you just want to get an o'scope for furthering your electronics understanding then definitly check out e-bay and try to find yourself an inexpensive scope. I picked up a real bargain for mine, only 30 bucks for a 500khz dual trace scope in bad visual shape but decent functioning shape. that'd be enough to get started but I already find I want to look at faster waveforms. 5-50mhz range would probably suit you better. Should be able to find something on e-bay for a few hundred. As far as chosing an o'scope and it's features from a TV repairs perspective you're probably best talking to a TV repair expert.

 

[jboettc208]

Waveforms

Thanks for the reply!

I guess I don't really know if I need an oscilloscope. Because I know very little about electronics I always purchase the service manual for the unit I am working on. I do this for a couple of reasons;

1.) Test locations and proper voltages for standby and operating power. 9 out of 10 times I find an improper reading and work my way backwards from that point on the schematic until I find the problem/problems.

2.) When I do find a component that has failed the service manual has a complete list of parts and part numbers so I know what to order.

I have noticed on all of the service manuals that I have purchased there are waveform test points with detailed illustrations and voltage information. I can't help but wonder if this would be a better way of troubleshooting or help me in pinpointing issues. DO you know if a frequency meter will measure these wave forms found in the service manuals or do I need an oscilloscope?

Thanks for taking the time to reply to my post. I do appreciate it!

Joe

Do you really need an o'scope? Most if not all of the functional parts of a television that are repairable can be tested with a simple frequency meter. Most of the complex waveforms in a TV set are from the image information itself. If you just want to get an o'scope for furthering your electronics understanding then definitly check out e-bay and try to find yourself an inexpensive scope. I picked up a real bargain for mine, only 30 bucks for a 500khz dual trace scope in bad visual shape but decent functioning shape. that'd be enough to get started but I already find I want to look at faster waveforms. 5-50mhz range would probably suit you better. Should be able to find something on e-bay for a few hundred. As far as chosing an o'scope and it's features from a TV repairs perspective you're probably best talking to a TV repair expert.

 

[tunedwolf]

For waveform analysis you will require a 'scope, frequency meters are for period and frequency measurement only I'm afraid. A good general purpose 'scope that will cover you working on consumer electronics should have ideally a bandwidth of around 40-100Mhz. If you plan on more serious work though, I would say 300-500Mhz will just about keep you covered depending on what you're doing with it.

If I was starting out again building my test bench, and had the money, I would be buying a Tek 2465B, for general purpose consumer electronics work though, the Tek 2235(without cursors) 2246(with cursors) are both winners in my book. There are loads of other good quality 'scopes around, especially of the far eastern variety, it doesn't have to be a major brand like Tektronix, Philips, Hitachi etc, or in fact cost you a small fortune. The only real drawback on buying a cheaper brand 'scope, is if it needs repaired, you will find it hard to get spares from any source other than the manufacturer or it's direct agents. Online auctions are fine to buy from, providing you can be sure of it's overall condition and return policy etc. Many a good deal is to be had from that source, but I would advise caution.

 

[Nigel Goodwin]

Thanks for the reply!

I guess I don't really know if I need an oscilloscope. Because I know very little about electronics I always purchase the service manual for the unit I am working on. I do this for a couple of reasons;

You NEED! a scope!, it's the next most important item after your multi-meter. For 99.xx% of uses even a 10MHz scope is more than you need, I would suggest looking at doublebeam 20 or 30MHz, but the higher you can afford the better - for the once in 20 years (or longer) you might need it!.

1.) Test locations and proper voltages for standby and operating power. 9 out of 10 times I find an improper reading and work my way backwards from that point on the schematic until I find the problem/problems.

You need to fully understand how it works, then you can make a start to find why it doesn't any more - TV's have many sections which depend on other sections, and tracing can be VERY difficult (if not impossible).

2.) When I do find a component that has failed the service manual has a complete list of parts and part numbers so I know what to order.

It's only specific parts that you need to order, most are 'off the shelf' parts (resistors and capacitors etc.) Mainly it's a question of experience, you tend to know the kind of things that fail, and looking at the circuit of a new set you can often spot design faults that you know are going to give problems later on.

I have noticed on all of the service manuals that I have purchased there are waveform test points with detailed illustrations and voltage information. I can't help but wonder if this would be a better way of troubleshooting or help me in pinpointing issues. DO you know if a frequency meter will measure these wave forms found in the service manuals or do I need an oscilloscope?

A frequency counter is a waste of time, for TV repairs (doing it all day every day), you might use one every five or ten years? - if that?.

 

[HiTech]

Everything Nigel put forth is gospel. As long as the scope can sync to the tv video you have it made. A scope, a good multimeter and an isolation Xformer make up the basic triangle for servicing many consumer electronics. All the other test equipment simply add to flexibility and provide more exact results. You can buy a used Tek or HP scope for what you'd pay for in new one of a mediocre brand like B&K. Leader makes a nice scope but it's falls short compared to Tek & HP. I wouldn't waste my money on cheap scopes unless you can get them for CHEAP.

 

[philba]

As others has said, a scope is an important addition to your tools. I bought my Tek 2250 (analog, dual trace, 50 mhz, portable) for $100 off ebay 2 years ago. It was out of calibration but worked perfectly otherwise. I was able to determine that it's calibration was pretty close so, it works very well for me.

If I were buying today, I'd look to spend up to $200 on a used dual trace 100 mhz uint on ebay. My preference is for Tek but HP is pretty good too. You might even be able to find a DSO in that price range. I saw a hitachi dual trace dso go for 112.50 - it appeared to be functional but you never know. Of course, you have to be careful and only buy from reputable sellers. Note that there are lots of DSOs listed for 300+ but many of them expire with no bids.

Note also that probes can be pricey and you will want 2 for a dual trace scope. units with probes are thus worth more.

 

[jboettc208]

sync to the tv video?

Is this a feature of some scopes? What should I look for?

Everything Nigel put forth is gospel. As long as the scope can sync to the tv video you have it made. A scope, a good multimeter and an isolation Xformer make up the basic triangle for servicing many consumer electronics. All the other test equipment simply add to flexibility and provide more exact results. You can buy a used Tek or HP scope for what you'd pay for in new one of a mediocre brand like B&K. Leader makes a nice scope but it's falls short compared to Tek & HP. I wouldn't waste my money on cheap scopes unless you can get them for CHEAP.

 

[Nigel Goodwin]

Is this a feature of some scopes? What should I look for?

Almost all scopes have a TV sync setting, it basically makes it lock better to either the line or frame sync.

 

[Sceadwian]

https://www.seanet.com/~bradford/ntscvideo.html
might provide some more basic information.
Mind you a 'generic' o'scope can be made more usefull for TV useage with the construction of basic external suport circuits, like a sync decoder which can provide seperate trigger pulses for the line and frame pulses.