We used to use the old Beckmans at work, where our power supplies were in the 1200V region. It wasn't that we were probing the HV supplies all the time, but HV sometimes appears in unexpected places. The supplies were fairly low current, so a big HV probe was sort of overkill. The survivability of the meters was much better than any others. They were reasonably accurate, but the selector switches wore out in commercial use. What really annoys me are meters with HV protection devices across the voltage input that short out the thing you're measuring, if you over voltage it. For handhelds, I want a Fluke if at all possible. Also, don't forget the bench meters. Fluke, Keithley, and HP have all made nice ones. The Keithley 175 or similar, the Fluke 8010 or 8050, and the little HP I mentioned above, are all decent for assembly and test on the bench, and can be had cheaply. BTW, I'm curious, how many people really believe they need true RMS? Examples?
I've got a Tektronix DMM916. Seems to be a pretty good meter, but then I haven't used it for anything really really critical.
I mainly got it because of the extra functions it has, capacitance, frequency, dBm, AC+DC volts, low voltage ohms, temperature, duty factor, handy little thing.
Pity they stopped making them in 2000. Mine gets used at work just about every day, and goes home in my toolbag at night, been holding up well for quite a few years.
Also, it will read two things at once, such as in this picture it's reading AC volts, and up in the corner is the freq reading of 60 Hz.
http://www.tek.com/Measurement/App_Notes/dmm916/graphics/dmm916-full.gif
I mainly got it because of the extra functions it has, capacitance, frequency, dBm, AC+DC volts, low voltage ohms, temperature, duty factor, handy little thing.
Pity they stopped making them in 2000. Mine gets used at work just about every day, and goes home in my toolbag at night, been holding up well for quite a few years.
Also, it will read two things at once, such as in this picture it's reading AC volts, and up in the corner is the freq reading of 60 Hz.
http://www.tek.com/Measurement/App_Notes/dmm916/graphics/dmm916-full.gif
Hi Conad,
The over voltage devices where there both for protection of the thick film divider and the operator in a Fluke.
An HV probe isn't overkill. Normal attenuators will heat up at that voltage and throw the reading off. Even HV probes, but at least they will not heat excessively at 1200 volts or so when they are rated for 30 KV. You could cal it with a Datron or some other calibrator and expect accurate readings from that - in that range.
They are cheap as well, so I can't understand why you wouldn't use one. Less expensive than the service to fix a meter.
-Chris
The over voltage devices where there both for protection of the thick film divider and the operator in a Fluke.
An HV probe isn't overkill. Normal attenuators will heat up at that voltage and throw the reading off. Even HV probes, but at least they will not heat excessively at 1200 volts or so when they are rated for 30 KV. You could cal it with a Datron or some other calibrator and expect accurate readings from that - in that range.
They are cheap as well, so I can't understand why you wouldn't use one. Less expensive than the service to fix a meter.
HP 34401A. One of the best bench meters for service ever made in my view. The true RMS section is critical when you are measuring a distorted waveform. That means almost any rectifier circuits or switching regulator supplies. Then there is the design work I do.
-Chris
Banned
Joined 2002
These are what i use, I got the fluke meter in a pawn shop 3 years ago, my dad had one and i loved it, so i was in the right place at the right time, paid 30$ for it, all it needed was a cleaning as the lcd was only half lit up. The other meter my dad gave me as a gift, i went out and bought a nice radio shack meter for $50 and he took it from me and threw it right in the garbage and handed me a real meter
An externally hosted image should be here but it was not working when we last tested it.
jleaman said:These are what i use, I got the fluke meter in a pawn shop 3 years ago, my dad had one and i loved it, so i was in the right place at the right time, paid 30$ for it, all it needed was a cleaning as the lcd was only half lit up. The other meter my dad gave me as a gift, i went out and bought a nice radio shack meter for $50 and he took it from me and threw it right in the garbage and handed me a real meter
An externally hosted image should be here but it was not working when we last tested it.
I have a good DMM but its LCD lost much light. How do you restore it by cleaning up?
Hi Salas,
This is assuming a Fluke meter or a similar meter. This is also assuming you are talking about display contrast.
-Chris
Take the LCD out and the conductive elastomers. Clean teh PCB contacts, the LCD contacts and both sides (lightly) with 99% alcohol. Reassemble without touching those surfaces.
This is assuming a Fluke meter or a similar meter. This is also assuming you are talking about display contrast.
True, but I think Dad was making an emphatic point. Once the point has been made the value of the cheaper meters is understood. Then you can use the cheaper ones in their proper context.
-Chris
Hi Salas,
My opinion is that you should get the most expensive Fluke you can reasonably afford. Then you should be very happy because that meter will serve you well. It this is the 115, then enjoy it. It's a very good meter.
First, remove the battery.
I would try a couple things. With liquid solder flux for electronics, lay a light coat onto the pins. Touch each pin with a hot iron. You may have to add a touch to "dry" connections. The goal is not to add any. There are times when the display is pushed into a "socket". In this case you can clean the display as you would any other. The contact fingers can be cleaned, then any cleaner washed out. Slightly re-tension them and carefully slide the display back in. If the fingers were bonded you may need to replace the display. Earlier meters applied and average DC voltage across the LCD display. This will degrade any LCD display. The newer meters have a special drive waveform for the digits and backplane that results in an average DC of very close to zero.
I seem to recall replacing the odd Metex display, but I can't be sure. Most meters seem to melt together in memories.
-Chris
My opinion is that you should get the most expensive Fluke you can reasonably afford. Then you should be very happy because that meter will serve you well. It this is the 115, then enjoy it. It's a very good meter.
Metex is better than some, not as good as others. I have one of those in my stock of meters.
First, remove the battery.
I would try a couple things. With liquid solder flux for electronics, lay a light coat onto the pins. Touch each pin with a hot iron. You may have to add a touch to "dry" connections. The goal is not to add any. There are times when the display is pushed into a "socket". In this case you can clean the display as you would any other. The contact fingers can be cleaned, then any cleaner washed out. Slightly re-tension them and carefully slide the display back in. If the fingers were bonded you may need to replace the display. Earlier meters applied and average DC voltage across the LCD display. This will degrade any LCD display. The newer meters have a special drive waveform for the digits and backplane that results in an average DC of very close to zero.
I seem to recall replacing the odd Metex display, but I can't be sure. Most meters seem to melt together in memories.
-Chris
I've blown up my trusty fluke 75 twice so far with excessive voltage. Theres a 1K fuse resistor inside that opens up. You can buy spares right from their website but with the $20 min order you should get 4 or so Which gets me thinking, theres two calibrated HP 34401s at work. Maybe its time to see how far off it is.
Which gets me thinking, theres two calibrated HP 34401s at work. Maybe its time to see how far off it is.
Hi astouffer,
If you are out, there are some trimmers inside. If you can find a dead 75, take one cover and drill holes in it directly above the trimmers. This will allow you to correct the higher AC response. Without the cover it will probably be out. You don't want to drill your cover.
I have a service manual for a 77 if you need (in PDF). I'll have to hunt around for a 75 manual. It should be out in the wild somewhere.
-Chris
It's a special part too! You should pick up a front terminal assembly and the gasket, as well as those darn elastomers (X2) with your order. Make sure you keep the rotary switch cleaned and lubricated so it lasts. It's the board that normally gets worn out.
I'm pretty sure you have a 4:1 TUR there, so it's a valid test.
If you are out, there are some trimmers inside. If you can find a dead 75, take one cover and drill holes in it directly above the trimmers. This will allow you to correct the higher AC response. Without the cover it will probably be out. You don't want to drill your cover.
I have a service manual for a 77 if you need (in PDF). I'll have to hunt around for a 75 manual. It should be out in the wild somewhere.
-Chris
Banned
Joined 2002
Banned
Joined 2002
anatech said:Hi Jason,
Make sure your bench can hold it all or you will find yourself in my situation.
You will love the scope once you pick one up. I bet you'll wonder how you got along without it.
-Chris
Edit: You can build your variable PSU once you have a scope (to check ripple and oscillation).
Actually, i'm looking for a professional or at least purchased one, I need one with positive and negative rails for working on power amps op amps and other things.
Like this one..
http://cgi.ebay.com/MASTECH-LINEAR-...6QQihZ015QQcategoryZ58286QQrdZ1QQcmdZViewItem
I have no idea how to use a scope, well i do a little but not really. I don't even know what to look for.
Any help anatech.? You live in Van where is a good place to buy from ?
id only use it for working on amplifiers nothing that needs a 500mhz id think a 100mhz decent 2 chanel would be nice..
Hi Jason,
Sorry. I live in ....... Georgetown. That's north west of the big smoke they call Toronto. It's a long plane ride to where you are!
I'm still using a dual power supply that I built years ago. I also use some HP supplies for work that requires a better supply. Bench suppies are not difficult to build. I even used a Japanese regulator IC in a SIP package. I'll be darned if I can remember the number right now.
I removed the power supply section from a Marantz 1180DC (heavy damage to case and PCB's). I stuck it in a metal case and use it with a variac when I am testing amplifiers that are new designs or projects. These are options you can take.
Even a 60 MHz dual trace is more than enough. I still use a Gould OS 255 (15 MHz), how's that for slow? Works fine though.
-Chris
Sorry. I live in ....... Georgetown. That's north west of the big smoke they call Toronto. It's a long plane ride to where you are!
I'm still using a dual power supply that I built years ago. I also use some HP supplies for work that requires a better supply. Bench suppies are not difficult to build. I even used a Japanese regulator IC in a SIP package. I'll be darned if I can remember the number right now.
I removed the power supply section from a Marantz 1180DC (heavy damage to case and PCB's). I stuck it in a metal case and use it with a variac when I am testing amplifiers that are new designs or projects. These are options you can take.
Tektronix 'scopes are very good. Sometimes they need work (everything I've bought off Ebay). Kenwood, Leader and a few others are very good as well. 100 MHz, two channel should be reasonable. If you can get cursors, they can make your life a little easier. Beware Philips Combi-scopes. They overheat and die.
Even a 60 MHz dual trace is more than enough. I still use a Gould OS 255 (15 MHz), how's that for slow? Works fine though.
-Chris
Banned
Joined 2002
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