Pages: [1]   Go Down

Author Topic: Radio Shack 22-7220 Multimeter  (Read 328 times)

GD6TWF

  • Member
  • Posts: 9
Radio Shack 22-7220 Multimeter
« on: May 08, 2021, 07:43:26 AM »

I am looking for a user manual and service manual for a RadioShack 22-7220 digital multimeter. I have tried googling it without success. Any suggestions of where to look? or if someone owns one would they be kind enough to scan the manual for me for me? Seems to be working on most functions but AC voltage, user manual may reveal why or service manual may help fix. 

Thanks in advance for your help
Logged

W7CXC

  • Member
  • Posts: 336
Logged

GD6TWF

  • Member
  • Posts: 9
Re: Radio Shack 22-7220 Multimeter
« Reply #2 on: May 08, 2021, 09:17:35 AM »

Thanks to W7CXC unfortunately the link is to a different model (22-813) and the two models have different functions, buttons and inputs.
Logged

KG6PHS

  • Member
  • Posts: 84
Re: Radio Shack 22-7220 Multimeter
« Reply #3 on: May 08, 2021, 09:22:40 AM »

That looks like a hard manual to find. Many times meter faults can be linked to dirty contacts in the main switch, or poor connections with the probes. These days you get a few more features for a lower price than before. I have recently got one like this, it seems well built.

https://www.amazon.com/AstroAI-Multimeter-Resistance-Transistors-Temperature/dp/B071JL6LLL?tag=kidmakcha-20&geniuslink=true
Logged

W9IQ

  • Member
  • Posts: 8866
Re: Radio Shack 22-7220 Multimeter
« Reply #4 on: May 08, 2021, 10:14:17 AM »

Many DVMs used the ICL7106 3.5 digit A/D engine or one of its many variants. A common technique for converting AC to its DC RMS equivalent involved the use of a CA3140 or similar op amp. If everything else in the DVM is working but you cannot read AC volts on any range, this is typically the culprit.

- Glenn W9IQ
Logged
- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

K7MEM

  • Member
  • Posts: 1058
    • JavaScript Electronic Notebook
Re: Radio Shack 22-7220 Multimeter
« Reply #5 on: May 08, 2021, 10:45:10 AM »

I have a Radio Shack True RMS Digital Multimeter (22-174B). I bought mine new in Jan 2006. Its much newer than the 22-7220, but has similar functions. My unit has Manual/Auto Range and much fewer main switch selections. What are you measuring, AC wise?

I don't know that a user manual is going to help. The instructions for each operation is basically the same: Set the switches correctly, connect the test leads, read the display. They only add extra precautions when you are dealing with high voltages.

On my meter, there are two main Voltage selections, V(DC) and V(AC), on the center function switch. The AC and DC are actually just symbols. AC is just a "Tilda" next to the V and the DC is a "dashed" line over a "solid" line next to the V. When in the AC Volts mode, a "blocking" capacitor is always in circuit.

Your meter probably has a "AC-CAP" switch. To measure AC Voltage, the "AC-CAP" switch needs to be enabled. This would place a blocking capacitor in series with the test leads. If you are having issues with the AC measurements, you might want to check the blocking capacitor and the associated switch.

Logged
Martin - K7MEM
http://www.k7mem.com

GD6TWF

  • Member
  • Posts: 9
Re: Radio Shack 22-7220 Multimeter
« Reply #6 on: May 09, 2021, 04:04:58 AM »

K7MEM is on the money all I needed to do was use the AC CAP button and it works. As you suggested mine is much older I think I bought it in the early 1990's when we had a RadioShack here in GD and it was an electronics/radio shop and not just selling consumer goods.

Further questions on functions

(1) Would like to know the range of the frequency function.
(2) It has two 1/2 inch slots marked "CX" would like to know the function?
(3) There are two buttons marked "Data-H" and "Peak-H". Peak-H I can guess as Peak Hold, the Data-H I am not sure about and what is the difference between the functions?





Logged

K7MEM

  • Member
  • Posts: 1058
    • JavaScript Electronic Notebook
Re: Radio Shack 22-7220 Multimeter
« Reply #7 on: May 09, 2021, 08:31:19 AM »

K7MEM is on the money all I needed to do was use the AC CAP button and it works. As you suggested mine is much older I think I bought it in the early 1990's when we had a RadioShack here in GD and it was an electronics/radio shop and not just selling consumer goods.


Glad it's all working. Sometimes the switched functions are not obvious.

Further questions on functions

(1) Would like to know the range of the frequency function.
(2) It has two 1/2 inch slots marked "CX" would like to know the function?
(3) There are two buttons marked "Data-H" and "Peak-H". Peak-H I can guess as Peak Hold, the Data-H I am not sure about and what is the difference between the functions?

I can only answer this in relation to the unit that I have.

(1) The max range, with 1KHz resolution, should be 2.000 MHz. My unit has several scales, so that I can obtain better resolutions, but yours only has one scale. All you can do it take what you get. The input Sensitivity should be around 500 mV p-p and the input Impedance should be around 1 Megohm in parallel with 50 pF. So don't expect too much from it.

(2) Those two slots marked "CX" are for measuring capacitance. The slots are used in conjunction with the switch positions marked "FARAD". It appears that your scales range from 2nF, which can be written as .002 uF or 2,000 pF, to 200 uF. The higher capacitance values are usually electrolytic capacitors. Make sure that any electrolytic capacitors are discharged, before plugging them in for a measurement.

When you are dealing with small values, you need to take into account the meter's internal capacitance. I keep a couple of low valued silver mica caps to use as standards. Before I make measurements, I use my standards to take a reading. That then gives me an idea of the internal capacitance.

My unit has the same two slots. I can use the test probes or the slots for measuring Diodes, Resistance, and Capacitance. The slots are often handier than the probes. The main function switch is use to select which is being measured.

(3) The "PEAK-H" button will let you freeze the measurement reading on the meters display. This is useful when you are trying to take a snapshot of a fluctuating voltage. The meter will not be able to make any more readings, until the meter is unlocked. Usually, to unlock the meter, you just press the "PEAK-H" button again. There should be a marker on your display that lets you know that the meter is in the hold mode.

The "DATA-H" button appears to be operational with the LOGIC selection on the main function switch. In the LOGIC mode, the meter would be being used to check logic circuits. Probably the meter would only show a "0" or "1" to indicate a logic state. The "DATA-H" button will, like the other "H" button, allow you to take a snapshot of the current logic state. Like the other "H" button, to release the meter for further use, press the "DATA-H".

Personally, I never found the logic functions very useful. In the day, there were hundreds of different logic probes. But the logic that I worked on was always operating too fast for them to be of any use. For my work I needed a high end Oscilloscope and a high end Logic State Analyzer. Even for the slow stuff, my choice was a scope.

Just an interesting point, is the function for measuring a transistor. On your unit you have 6-pin socket that works in conjunction with the "hfe" selection on the main function switch. If you plug in the transistor the correct way, you can get a "hfe" reading. On my unit, I only have a 3-pin socket that just says "hfe" and has a "TEST" button next to it. If I select the "hfe" function position, insert a transistor in the 3-pin socket, and then press the "TEST" button, the display will tell me whether it is a NPN or PNP, the ordering of the pins (E, B, C), and the "hfe". This has saved me several times when working with bagged transistors. It seems that the 2N2222s, and maybe others, can have different pinouts.

Well, that's probably more than you wanted to know. On some of the issues, I made an educated guess. So if anyone spots something totally wrong, please correct it.
Logged
Martin - K7MEM
http://www.k7mem.com
Pages: [1]   Go Up