Yokogawa 7534-03 Multimeter

Yokogawa 7534-03 MultimeterJapanese equipment maker Yokogawa made handheld DMMs for HP before HP became Agilent.  This 3200 count 3½ digit Yokogawa-branded model is very similar in appearance to the HP E2378A model.  Unlike the HP, this unit adds a high-impedance ‘ADP’ mode, presumably for current-clamp attachments and the like.  Otherwise, it has a very fairly mundane feature set.  It is also the only multimeter I’ve ever seen with a ‘Data Hold’ button on both the top and the side.

Opening the case reveals an obvious problem.  Something has gotten very hot and burned part of the circuit board.  There are burn marks on the inside of the case as well.  The resistor (R6) that died violently has already been removed.  There is a pencil-written note on the side of the unit that says “4.9 Ω 2 watt wirewound resistor”.  In retrospect, I realize this may have actually said “4.99 Ω”, but since it’s now been cleaned off, we’ll never know.  In any case, it was certainly helpful for someone to note what had been removed from the device.

Some simple testing shows that the DC voltage measurement function is still working and is reasonably well-calibrated.  Resistance measurement also works.  Only the current ranges do not work.   The meter passes current in the μA and A ranges but reads incorrectly.  No current is passed in the mA range, so the conclusion is that the missing/damaged resistor is the mA range current shunt, and is probably part of the voltage sense circuit for the other two ranges.  No schematics or service information can be found, so we’ll have to go on probabilities here.

Closer examination of the burnt PCB reveals that the larger copper traces are intact and relatively undamaged, aside from lifting slightly from the board.  There is one small trace missing that leads to a 1/8W 3.3K resistor, which is in parallel with the missing shunt resistor R6.  That doesn’t make a lot of sense, unless the designers intended to ‘trim’ the shunt a bit for more accurate readings.

Due to the amount of possible heat damage, the resistors surrounding R6 were removed from the board for testing.  All measured correctly, so the damage was limited to the shunt and the PCB itself.

4.9Ω 2W resistors are hard to come by, either in my spare parts inventory or from a parts supplier, so it looks like a non-ideal solution might be called for.  To start off, I tacked in a standard 4.7Ω resistor and checked the operation of the meter.  The current ranges all worked.  In fact, the A and μA ranges were OK.  The mA range was just a bit too low.  I decided it may be possible to substitute two parallel 1W 10.0Ω 1% precision resistors I had on-hand in place of the shunt, and then replace the ‘trim’ resistor with whatever produced accurate readings.  Again by experimentation, 600Ω was determined to work well.  So the 3.3K ‘trim’ resistor was replaced with a ¼W 600Ω 1% metal film resistor.

The resulting combination of the 2 10Ω and 1 600Ω resistors actually measured 4.98Ω.  This is where I decided that the note on the side of the unit might have actually been 4.99 instead of 4.9, because 4.99 in parallel with the original 3.3K trim resistor is 4.98Ω.  Also, I found a picture of the inside of an HP E2378A.  It had a slightly different layout, but R6 was clearly marked “5.020”.

Given the nature of the malfunction and the somewhat um… ‘ghetto’ nature of the repair, a good check of the meter’s ability to measure current is in order.  Side-by-side comparison with another dependable DMM reveals that the repaired meter is reading quite accurately.

So let’s call that success, and make a few more observations.

This meter is quite ruggedly built.  The sturdy case halves are gasketed and fastened together with 4 machine-threaded screws going into big brass threaded inserts.  The input jacks have o-ring seals, and the lens is permanently sealed in.  The buttons are also sealed in with a metal retaining piece.

There are unpopulated footprints near the input jacks for what appears to be two MOVs and a spark gap, components that would provide over-voltage protection.  That, in combination with the use of small fuses, indicates this meter would not be considered appropriate nowadays for use with high-energy circuits.  Perhaps that’s the reason it has a warning sticker on the side that is remarkably at odds with the 750V~/1000VDC rating on the top.

DMMCheck calibration check results for this Yokogawa 7534-03:

Reference Reading Notes
DC 5V 5.00
1mA 1.00
AC 5V 5.55 nominal for non-TRMS is 5.55
1mA 1.09 nominal for non-TRMS is 1.11
Ohms 100Ω 99.9 0.1 with leads shorted
1K 0.998K
10K 9.98K
100K 99.8K

About modemhead

Fixologist and multimeter junkie.
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19 Responses to Yokogawa 7534-03 Multimeter

  1. Philip says:

    Hi,I‘ve got a E2377A and that is almost the same as yours but now all the measurment is not right and I want to know how to calibrate it could you give me some help?

    • modemhead says:

      Hi Philip. I no longer have this multimeter in my possession, but in looking through my notebook I found these notes:
      RV1 (DC)
      RV2 ?
      RV3 (AC)
      RV4 (Temp)

      Highly recommend cleaning the circuit board using isopropyl alcohol (strongest you can find) and allow time to dry. Contamination on the board can cause bad readings. Then using another trustworthy DMM, compare the readings with a stable voltage source at about 3.00VDC. Tweak the DC cal pot only if they don’t agree within a few counts. This is obviously not the most ideal means of calibration, but should suffice for basic home/hobby use.

  2. Philip says:

    Thanks so much for your reply, but I still want to ask you for some circuits of this multimeter,and I had know that soar 4050 also share almost the same circuit. Certainly, If you had and kept that, whatever I would try as you said and share with you if any progress.

    • modemhead says:

      If I understand you correctly, you need the schematic for this meter. I am sorry, I never found one, which is why I had to do some guessing during the repairs. And you’re always welcome to share your progress.

  3. Philip says:

    O,I see, That’s my fault , my English should need to be improved. Now I have solved some problem and the measurement function is able to work but not precious,for example, at the DC voltage measurement when the probe is shorted it donot say ‘0’,but a negative number decreasing, and the positive and negative number it says is not the same absolute value ,the difference was very huge about 500mv until just now when i shocked it ,the difference suddenly fall down to about 3mv““That’s amazing ,and I want to know why.
    Sorry to disturb you all these days ,and let you read this terrible not easy to understand words.

    • modemhead says:

      Your English is better than my Mandarin. I am still not sure exactly what the problem is, but I think what you are describing is most likely caused by tiny leakage currents through circuit board contamination. The input to the A/D convertor on any DMM is very high impedance, on the order of giga-ohms, and is easily disturbed by very very tiny currents. It does not hurt to clean the circuit board multiple times, you may see some improvement.

  4. Newton says:

    Hi , I have a multimeter E2378 model, but isn’t working. It’s an old equipment, but I want to use it . I opened to see what is wrong and there is PTC and I don’t no what is the value of that component . Can someone help me?

  5. Samuel says:


    I inherited three Yokogawa 7533-03 DMM’s. What exactly does the ADP setting do?

  6. Thevinis says:

    My LCD display is not functioning , is there anymore replacement part for this model >

    • Charles Patten says:

      It may be that the microprocessor isn’t running resulting in a blank LCD. The oscillator components are under the battery holder.

  7. Henrik says:

    Better late than never to find this page. 🙂
    I just found a SOAR 4040 multimeter, that has many similar features. Auto-ranging sounds so cutely clicking, I guess it switches with relays inside. Hehe.
    Anyone got a manual for this, or can tell me what the “(triangle sign)REL” button does?
    The rest are fairly self-explanatory. Hz, VAC/VDC, Ohm/beep, diode check, ADP, A(amps)AC/ADC.
    I’m glad I found it, it’s so easy to use. Well, compared to the multimeters with a huge rotary dial for various voltage and amp ranges. 🙂

  8. Nunzio says:

    The problem with my HP E2377A DMM is that LCD is Blank. As I touch the crystal S153 under the battery holder with a lead of an other DMM the LCD switch on for a while.
    I changed a resistor 470K ohm near the capacitor (nex to the crystal)because it had a almost disconnected lead.
    I would like to change the crystal, can not find replacement.
    Any one who knows what does S153 mean? It is written on the radial crystal.
    15 KHZ perhaps?
    Thanks for answer

  9. Darren Walker says:

    Did you change R26 ? I’m in the process of restoring the HP E2378A. Battery leakage caused a display failure. I’ve removed the battery casing and had to remove R26 and C13 as they were both basically dissolved.
    If someone can confirm the value of C13 and R26 it would be greatly appreciated. Very nice build quality overall and a gem to behold on the workbench.

  10. Dave Alan Caruana says:

    A thank you for your great article.. my 7534-02 was giving wrong readings eg. 3.65v for a battery which was actually at 3.863v .. the error was sort of constant so two batteries in series would not give double the voltage, still about 0.2v off. Another issue I noticed was it would show a voltage and gradually creep up, like a capacitor charging slowly.

    The other problem was the last digit on the LCD seemed to have not enough contrast – the initial display lighting all segments was a mess but in use it was useable.

    First I tried the calibration .. wouldn’t go far enough.

    Next I tried cleaning the board. There was brown stuff coating the underside of the board – I thought it was some sort of conformal coating or maybe flux from soldering – but not – adding 99.9% alcohol made it very sticky. I scrubbed well with a tooth brush and more alcohol. Also unscrewed the holder for the display and cleaned the contacts there.

    On reassembly it didn’t work.. quite concerning.. but when I tried to check the current draw with another multimeter I realised it was just the battery contact not making contact.

    Readings on voltage immediately improved and I was able to calibrate it at approximately the factory setting (around 1 o’clock on the trimmer).

    Only issue left is that while the display test at power on is great, in use it is a bit faint – not unusable but could do with a bit more ‘brightness’.

    Thank you again for giving me the courage to go at it – there is precious little info online!

  11. nik says:

    Those internals really do resemble the Fluke 70 series internals.

  12. Dan Kahn says:

    I am troubleshooting an HP E2378. The resistance function shows OL with the probes disconnected and 00.0 with the probes connected. Any resistance value displays 00.0.
    The meter was dropped during a resistance measurement if that has any correlation.
    Other functions such as Voltage both AC and DC work correctly.

  13. Dan Kahn says:

    I determined the cause of the problem was a broken PTC component. It is labeled TDK 9309. I think it is some kind of temperature sensing resistor.

    Any clue as to a replacement?

  14. Dan Kahn says:

    The part is a PTC resistor for current sourcing in the Resistance mode of the DVM. This probably compensates for temperature variations. The value on two different meters was 900 to 940 ohms. Since i will probably not be using this in extreme temperatures, I substituted this with an 820 and 100 ohm resistor is series.
    Measuring a known good 500 ohm resistor indicated 502 on the meter. This tels me the fix is good enough for me.
    I also repaired an non working 2378 I purchased to determine what the missing part was so now I have two. Thinking of selling the one I repaired.

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