TekPower TP4000ZC / Digitek DT-4000ZC: Looking for Schematic

[Electro Fan]

Anyone have a schematic?

There are several (4?, see photo) adjustment points on the PCB - just trying to figure out which one controls voltage - but knowing what they all do would be extra good before twiddling them.

[Electro Fan]

Maybe instead of using a schematic someone might be able to determine from just looking at the board which one is the likely voltage adjustment point?  Thx

[Lightages]

Even if you don't get an answer, you can work it out fairly easily. Pick one pot, set for a function, attach a known value for that function, and twist the pot. If the reading didn't change, move to another function on the dial, attach an known measurement value  for that function, and twist again. Repeat until you find which function matches the pot.

Of course, you should characterize each measurement function with known test values before you start this.

In the end, you will have mapped all the pots.

[retiredcaps]

Maybe instead of using a schematic someone might be able to determine from just looking at the board which one is the likely voltage adjustment point?  Thx

Use freeze spray as per this video (about 4 min in)

[Lightages]

Great idea! That way you mess with nothing and know which is which! Even easier and cheaper, use a soldering iron to touch each one for a bit to see what changes.

[Electro Fan]

Thanks for the video - I was just about to order up the cold spray but I saw the suggestion to save some $ with the soldering iron - so I gave the soldering iron a shot.  Turns out that the adjustment point that was the most voltage sensitive to the heat wasn't the adjustment point that actually adjusts the voltage.  Lesson learned.

Turns out that #4 in the photo is voltage, and #3 (just I guessed due to the proximity) is the current.  In the process I might have twiddled #2 and #1 a bit - I'm not sure yet what they do, or if I really moved them. 

BTW, I thought I needed to get deep into the adjustment point to twist the inner axel but what really goes on is that each adjustment point has outer rim with a cross hatch pattern - so the rim drives the axel.

After figuring this much out I was able to get the voltage to agree with two Voltage Standards and my Fluke 179 to within 1 millivolt (previously I was out by about 6 milliVolts:  2.042 before adjustment vs. 2.048 target on the Voltage Standards).  I was concerned because the 2.048 V reference point seemed to be further out than the lower (1 V) and higher ( 3, 5, 10 V) references - but when I got 2.048 nailed the others snapped into alignment surprisingly well.  I had previously done this on a Radio Shack DMM and it worked well but the adjustment points on the Tekpower seemed a little less finicky and more linear.

I also was able to dial in the current using #3.

Without knowing what #2 and #1 do I tested some resistors and capacitors.  Resistors seemed to line up to within about a tenth of an Ohm and capacitors were good to a nanoFarad or so.  Almost hard to believe, I know.

The only thing that has me slightly concerned is that the voltage on the diode setting is only about 1.6 V - not quite enough to illuminate a red LED.  The Fluke puts out over 7 Volts.

I'm going to do some more testing and research (read the Tekpower specs if I can find them).

EF

Update - found this Tekpower spec:  Diode test: 25uA,3.0V

If anyone has a TP4000ZC (or DT-4000ZC) and can test a LED and regular diode and/or figure out what #2 and #1 do, please post your findings.  Thx

[retiredcaps]

Update - found this Tekpower spec:  Diode test: 25uA,3.0V

Manual at

http://www.multimeterwarehouse.com/TP4000ZC/Data%20logger%20%20Manual.pdf

Specs in manual say

Diode testing:
 Test current : 1±0.6mA
 Test voltage : .Approx.. 1.5V

[retiredcaps]

The only thing that has me slightly concerned is that the voltage on the diode setting is only about 1.6 V - not quite enough to illuminate a red LED.  The Fluke puts out over 7 Volts.

It is good to have multiple meters with different source diode/ohms voltages.  The Fluke might turn on some components when used to measure in circuit.

[Electro Fan]

The only thing that has me slightly concerned is that the voltage on the diode setting is only about 1.6 V - not quite enough to illuminate a red LED.  The Fluke puts out over 7 Volts.

It is good to have multiple meters with different source diode/ohms voltages.  The Fluke might turn on some components when used to measure in circuit.

Thanks retiredcaps,  I must have copied the specs from a different/wrong model.  When I measure the diode test I get 1.59V and 0.67mA.  I guess it's running properly.

[Electro Fan]

A further update.

Adjustment point #4 is definitely DC voltage.  #3 seems to adjust AC. 

After some trial and error it seems like 3 and 4 want to work together (but I could be wrong).  I tried getting 4 dialed in first with a Voltage Standard; it creates very repeatable DC voltages to the milliVolt.  Then I adjusted 3 to conform to the Voltage Standard specs for AC current  (I got within 2 hundredths of a milliamp).

#1 is definitely for temperature.

#2 remains a mystery.

Resistors and capacitors seem to measure properly - not as well as DC voltage but reasonably in the ballpark.  The PC monitoring feature (with RS232 cable and software) is pretty simple/basic but maybe ok for logging something.  It also comes with a thermocouple and it reads temperature without the thermocouple plugged in.  On the DMM you can only get degrees C; on the computer you can get C or F.  It's not going to put Fluke out of business but for $35 including shipping it's an ok meter.  If it could power LEDs and do TRMS I'd be pretty enthusiastic about it. 

[mtdoc]

This is a great meter for the price IMO.  I bought  one a few years ago wnen i needed a meter that would do datalogging. it works great with QtDMM.

Accuracy of mine has always been spot on. No need to adjust anything. Martin Lorton did a review of this meter a while back.

[nixxon]

This is a great meter for the price IMO.  I bought  one a few years ago wnen i needed a meter that would do datalogging. it works great with QtDMM.

Accuracy of mine has always been spot on. No need to adjust anything. Martin Lorton did a review of this meter a while back.

I haven't heard of QtDMM before. I found UltraDMM here at eevblog after a search, because the software that came with the TP4000ZC was so bad. Do you know if QtDMM has any useful features that UltraDMM does not support?

[mtdoc]

This is a great meter for the price IMO.  I bought  one a few years ago wnen i needed a meter that would do datalogging. it works great with QtDMM.

Accuracy of mine has always been spot on. No need to adjust anything. Martin Lorton did a review of this meter a while back.

I haven't heard of QtDMM before. I found UltraDMM here at eevblog after a search, because the software that came with the TP4000ZC was so bad. Do you know if QtDMM has any useful features that UltraDMM does not support?

I haven't really used UltraDMM - I downloaded an early version which was buggy and kept crashing - so I can't say.  QtDMM is Linus/OSX only I believe and UltraDMM is Windows only isn't it?   For low power, long term loggging - QtDMM on a Rasberry Pi works great!

[plurn]

Hi,

Thanks for the info in this thread. I have been looking into how to adjust the calibration of my old Digitech QM1538 multimeters from Jaycar and I did not want to just randomly try changing the variable resistors. The QM1538 seems to be pretty much exactly the same as the TP4000ZC with only a few slight differences. One difference being that the QM1538 electrolytic capacitors are branded Rubycon - though I suspect they are really One-Hung-Low brand.

I am getting from 0.1 to 0.8% DCV discrepancy in the lower ranges compared to my newer more accurate multimeter so hoping to get that to be a bit tighter.

Some tags so others wanting to adjust this multimeter can find this thread - Digitech QM1538 calibration adjustment