Re: Fluke 87 issue
It would be nice to know what "my Fluke went out" means. Like RC asked, does it power up, does it measure anything on any range at all? These are much better clues to the possible faults than trying to trouble-shoot by measuring various components in-circuit. More often than not, that leads to red herrings. It is unlikely that those two SMD resistors are bad.
If there is any hint of corrosion at all, the best plan of action is to start with a full-immersion bath in strong isopropyl alcohol and scrub the board with a brush. (*Carefully*...
modemhead
Lurking
Last Activity: 11-25-2019, 09:01 PM
Joined: 06-16-2012
Location: North Carolina
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Re: AC Adapter problem.
Cheap multimeters are DC-coupled on the ACV ranges (ie. they have no DC-blocking capacitor). They also have a single diode rectifier for AC-to-DC conversion. The reading is scaled to display 2.2 times the average of this half-wave rectified signal, which for a sine wave, would approximate the RMS voltage.
Because of this design: 1) cheap multimeters are not useful for measuring very low AC voltage because the rectifier forward voltage drop begins to create significant error below say 10V or so. And 2) they definitely will not accurately...Leave a comment:
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Re: Should a transformer live/neutral pins have continuity?
For testing, don't use speakers that you care a lot about. Normally a quiet amp will have near zero DC voltage output. A malfunction can cause it to output a significant amount of DC, which can destroy a speaker by heating up the voice coil....Leave a comment:
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Re: Mastech ms8229
Here you go. It's a Cen-tech P98674, looks pretty much like a Mastech MS8229....Leave a comment:
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Re: Ever used the hFE tester on your multimeter?
Never. For me, diode-test function suffices for general-purpose transistor checking.
The sockets are unreliable on every meter I've ever touched with this "feature". They all tend to flash a lot of non-sense numbers while you're wiggling it around. I have no patience for that.
If I am really interested in the beta, I'd use a transistor tester where the collector current is known and preferrably can be varied to match the type of transistor.Leave a comment:
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Re: Fluke 87 III display issue
LCDs segments are like little capacitors, and are driven with a high-impedance low-frequency AC signal. Usually there's enough of a AC mains-induced signal between the end of your finger and earth ground to activate an LCD segment. I've used this as a quick test of LCDs before.
If you hold the LCD glass in the light just so, you can see the conductive traces around the edge. Find the H1 connection and touch it lightly with a probe that is connected to earth ground. (Don't use a sharp probe, obviously.) Then run your finger over the other...Leave a comment:
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Re: Fluke 87 III display issue
I agree with retiredcaps, something's wrong with the H2 line. In the all-segments-on test, everything on that backplane is missing, but all others are on with good contrast. So probably not a matter of lowered voltage or bad connection, it looks more like no connection at all. Which means either: bad driver in the chip, bad LCD, or a broken connection in-between.
Try to eliminate the LCD by seeing if you can get some of the missing segments/annunciators to come on with the LCD out of the meter. For example, a 3 to 5Vp-p 50Hz square wave...Leave a comment:
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Re: Can AC coexist with DC?
Measure a 9V battery with your DMM set to ACV, red to the positive battery terminal, black to the negative. If it reads 18V or so, it's the meter. If you switch the leads around, it should read zero....Leave a comment:
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Re: Can AC coexist with DC?
May I ask what kind of multimeter you are using to measure this?
The reason I ask is that many less-expensive multimeters use DC coupling for the AC voltage ranges (ie. no DC-blocking input cap.) This causes the meter to give a non-zero reading for any positive DC voltage applied while the meter is set for ACV. Due to the scaling used for AC, the reading will be about twice the DC input. Negative DC voltage will give a zero ACV reading however, because the meters use a single diode as a half-wave rectifier for AC.Leave a comment:
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Re: DMM calibration
If the job requires it, then a professional calibration is necessary.
But for hobbyists and weekend warriors there are other solutions. You could find a friend with a new or recently-calibrated meter and compare readings. There are also some reasonably-priced voltage references available:
[url]http://www.voltagestandard.com/[/url]
[url]http://www.gellerlabs.com/Voltage%20References.htm[/url]
You can make your own with one of the various voltage reference chips available, but the advantage of ordering one from...Leave a comment:
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Re: My new (used) Fluke 87
With glue-type repairs, you never know how it's going to hold up, but yours looks good. The reinforcing material is a great idea.
We used to call the value engineers "screw shorteners". In this case I think they went overboard. But Fluke did indeed go back to screws (4 of them) in the 87-V generation.
Always interested in good repairs! You have my email address. No hurry....Leave a comment:
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Re: My new (used) Fluke 87
Nice find! Looks to be in excellent condition, especially with the clean-up job.
The viewing angle thing is just a property of that LCD. It has the best contrast at a slight downward angle. Somewhere in the fog of my brain I remember reading something about that being a design trade-off, bias voltage vs. minimum operating temperature and other things I don't understand. The III and V generation displays are improved a bit in this respect.
Being new to using an 87, here's something to be aware of. It LOVES to take itself...Leave a comment:
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Re: TDK 517 component - can anyone identify picture
The red rectangular component looks like it could be the AC coupling capacitor. I am unfamiliar with 86x meters, but often this cap is designated "C1" in many Fluke meters. The photo is a little fuzzy, but it also looks like there could have been an arc from an over-voltage event between the thermistor and the cap. The cap could be damaged which would affect all AC functions.
Take it out and test it if you have the means. You can TEMPORARILY tack in a 0.01uF to 0.1uF capacitor you may have laying about...Leave a comment:
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Re: FLUKE 8050A searching adjusting tip to set DC at 0000
The front end of the power supply in this meter is a constant-current source. Despite its simplicity, it is safe and effective for trickle charging NiCd cells in the 1200mAh to 1800mAh range. A healthy 4.8V pack will develop a voltage generally between 4.8 to 5.6V depending on its state of charge. This voltage is used as the sole means to regulate the difference between the meter's -5V DC rail and its -10V rail.
Operation outside these parameters is therefore, in a phrase, [I][B]not recomme...Leave a comment:
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Re: FLUKE 8050A searching adjusting tip to set DC at 0000
Just for reference, here is how the original pair of 2.4V packs (4.8V total) are connected....Leave a comment:
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Re: FLUKE 8050A searching adjusting tip to set DC at 0000
It is a very simple charging scheme. With the power switch off, the LM317 provides about 140mA of charging current via R26. This is a reasonable trickle-charge rate for basic 1300mAH NiCd cells, and should bring up a flat pack overnight.
With the power switch on, the current is increased by another 100mA via R25, to power the meter and continue charging the battery at a slightly reduced rate. If I recall correctly, the meter uses about 150mA.
The charging LED is always illuminated when the power...Leave a comment:
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Re: FLUKE 8050A searching adjusting tip to set DC at 0000
From your pictures, it appears that you do have the battery-powered version (option 01), except that the batteries have been removed. The small toroidal transformer, and also R26, do not exist in the AC-only model.
It is not good to run this meter without the batteries. The power supply consists of an LM317 configured as a constant-current source. The design depends on the batteries being there to regulate the voltage to near, or just above, the nominal 4.8V. Without the batteries, the voltage will rise much...Leave a comment:
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Re: FLUKE 8050A searching adjusting tip to set DC at 0000
I have several 8050As, and that looks perfectly normal to me. The one I use on a regular basis stays powered up 24/7, usually on the 20V range, and it bobbles constantly between 0.000 and 0.001, even with the input shorted. I have found it to be very trustworthy in terms of accuracy.Leave a comment:
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Re: FLUKE 8050A searching adjusting tip to set DC at 0000
If you short the input and it reads zero within about 1 count, I wouldn't worry about it. I also would not use the Rel function to attempt to null a residual reading, because there is no guarantee that any small offset is constant once a low-impedance voltage source has been applied to the inputs.
There is no zeroing adjustment that I know of in an 8050A. The A/D converter includes an auto-zeroing phase that stores any non-zero error offsets in the system on tantalum capacitors C8 and C33, and subtracts them...Leave a comment:
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Re: Model 87 Funny Noises
Sounds like the lead alarm going off. Are the leads in the correct jacks? Black to COM, Red to V-Ohm-Diode. If that's OK then look for foreign matter or damage in the mA or A jacks.Leave a comment:
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