Fixing an old Voltcraft VC 650 - Page 1
Forum section: electronics / repair

author: Cold-1
author_rank: Contributor
timestamp: March 19, 2015, 05:15:06 pm
content: Hi,I have an older Voltcraft VC 650 Multimeter. I can turn it on, the display works, as does switching all the measuring positions and ranges. Also the menu works ok. But it seams, all the input sockets are dead. No matter what I try to do with the probes, the meter stays at the initial values. I have already checked the fuses, they seam ok.The PCB looks pretty messy, there are a lot of hand made additions.Is there any way to just point at a component and say "that's the culprit"?Regards

author: retiredcaps
author_rank: Super Contributor
timestamp: March 19, 2015, 05:34:40 pm
content: I'll try to help here. Let me ask some questions.1) If you try to measure a 9V battery, what does the VC650 show?2) With nothing connected and the VC650 set to resistance, what does it show?3) Connect a 1k ohm resistor (or any resistor), what does the VC650 show?4) Set the VC650 to resistance mode. If you short out the leads, what does the VC650 show?5) Did the VC650 just stop working or was it subjected to high voltage (say 500V or more)?6) What happened to the fuse on the mA fuse? It looks rather odd? Is that aluminium foil?PS. Most modern multimeters only use fuses for protection of the current range. That is, the multimeter can still measure voltage and resistance with blown/bad fuses.

author: Cold-1
author_rank: Contributor
timestamp: March 19, 2015, 05:58:19 pm
content: Hi, thanks for the fast reply. Ok, I try to answer the questions:1) It just shows "0L V" (This is shown after initialisation).2) It shows "0.L MO"3) Same as 2)4) Same as 2)5) I can't say. I know I lent it to some one at that time (it's been a while) and whet it got returned, it was in the current state.6) Yes, thats foil around it. It got worn a bit when I took it out to measure it.

author: Lightages
author_rank: Unknown
timestamp: March 19, 2015, 07:15:31 pm
content: Wow! That thing is a real mess. Terrible construction and bodges everywhere. It is not surprising it has failed. You need to check each component that is connected to the volts/ohm jack. ne of the resistors or a PTC has gone open, or there is a cold solder joint. If you have the option, save your time and buy something better.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 19, 2015, 08:13:47 pm
content: 7) I forgot to ask what the VC650 shows on the lcd when set to DCV with no probes attached?Regarding 5 and 6, if the person who borrowed it tried to measure voltage while the meter and probes were inserted into the mA jack, I can see the main IC getting fried because the mA fuse was hacked with aluminium foil! Fuses are supposed to blow if too much current to protect the user and the meter.I found a schematic of the VC650. The quality isn't great, but it is better than nothing. I'm still learning how to read one so it will take a while for me to digest all the pages. More test points/checks to come later tonight or tomorrow depending on my time.http://elektrotanya.com/voltcraft_dmm_vc_650_sch.pdf/download.htmlIt also includes a Bill of Materials.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 19, 2015, 08:32:59 pm
content: The schematic for the VC650 suggests it uses an Intersil 7135 IC.http://www.intersil.com/content/dam/Intersil/documents/icl7/icl7135.pdf8] Can you verify this is the correct IC? It is likely underneath the lcd. I count a 28 pin IC on the pcb backside.9) If this IC is blown/bad, replacements are available on ebay for reasonable prices. $3.29 USD + free ship.http://www.ebay.com/itm/171555349966I have no experience or financial affiliation with the seller. The 7135 may be available in your country at similar prices from reputable distributors like digikey, mouser, farnell, etc. It is $5.21 USD on digikey and mouser.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 19, 2015, 09:35:17 pm
content: Some more tests.10) The 7135 datasheet shows pins 9 (IN LO) and 10 (IN HI).a) Put your VC650 into DCV.b) Use the VC650 to measure 5V DC (like standby power from an ATX PSU or some wall wart ac/dc adapter - it doesn't have to be exactly 5V, just something close).c) Report VC650 lcd display result.d) Using another multimeter, measure the DC voltage across pins 9 and 10 of the 7135. The black probe should go on pin 9 and the red probe should be on pin 10. Keep the VC650 connected to the 5V DC source during this test.e) Report your reading for pin 9 to 10.11) Measure input impedance of the VC650 when it is in DCV mode.a) Put your VC650 into DCV.b) Using another DMM, put it into resistance mode.c) Put other DMM red probe into the V/ohm jack of the VC650.d) Put other DMM black probe into the COM jack of the VC650.e) Report the other DMM reading in ohms.12) Measure the voltage of the VC650 when it is in ohms mode.a) Put your VC650 into resistance mode.b) Using another DMM, put it into DCV.c) Put other DMM red probe into the V/ohm jack of the VC650.d) Put other DMM black probe into the COM jack of the VC650.e) Report the other DMM reading in DCV.

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 19, 2015, 11:12:25 pm
content: Agree, something seems open. This awesome work of art has a two-coil latching relay right at the inputs.Sheet metal logic is definitely a possible failure point. Next one is the big 10Meg resistor right beside the relay. Then a couple of 4051 mux chips, U4 and U5. If the bottom end of the divider was not grounded through U4, you'd get an OL for practically any input.As suggested, troubleshoot in DCV mode with known input, and try to trace it along through the divider and on to the ADC.

author: gilbenl
author_rank: Regular Contributor
timestamp: March 19, 2015, 11:19:17 pm
content: This doesn't look right (red circle). Might be the photo though.

author: Cold-1
author_rank: Contributor
timestamp: March 20, 2015, 04:00:41 am
content: Wow, you guys are great...@gilbenl: This is just a bad angle of the photo. The resistor is solderd ok.@retiredcaps:Yes, this is the right IC.I will do all the other tests when I get home from work. Have a long day in front of me...Regards

author: retiredcaps
author_rank: Super Contributor
timestamp: March 20, 2015, 04:51:41 am
content: For test 11, your other DMM will have to measure at least 12 or 13M ohm. The cheap $5 830s only measure up to 2M ohm.

author: Cold-1
author_rank: Contributor
timestamp: March 21, 2015, 12:18:26 am
content: Ok, here are the measurements for 11) and 12):11) Very interesting: One DMM (a Voltcraft 820) shows 7.4 M ohm, my Fluke 87V shows 0.9 M ohm12) Again, Voltcraft and Fluke different: For the former, it changes from 124mV to 126mV, for the latter it changes from 63mV to 76mVEdit: I just measured some reference resistors, and they are correctly identified on both meters.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 21, 2015, 01:38:56 am
content: Test 13.13) Based on your results for 11, here is test 13.a) I have circled what I think is R77 in the schematic. It should be a 10M ohm resistor (brown, black, black, green, blue = 10M ohm 0.25%).b) I suggest desoldering one leg and verifying out of circuit it is 10M ohm with the Fluke 87V.PS. Your Voltcraft 820 is a rebadged Uni-Trend multimeter.PPS. Don't forget about test 7 and 10.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 21, 2015, 01:45:07 am
content: 14) When the VC650 is in DCV function, does it start autoranging from the mV or V? I can't seem to find an user manual and pictures of the VC 650 front are very small on the Internet?

author: Cold-1
author_rank: Contributor
timestamp: March 21, 2015, 09:30:18 am
content: Hi,7) It says "0.L V"10c) "0.L V"10e) "1.3mV"13) Fluke says 10M ohm14) When turned on, it starts in VAC mode. When swithing to DC, it autoranges at V, not mVI have ordered 2 ICs for 5 bucks. If the one on the meter is really fried, I will replace it and at the same time put in a socket, if there's enough clearing from the display.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 21, 2015, 11:13:32 pm
content: So let me summarize what has been reported. R = reported.R1) VC650 displays 0L on DCV with no probes attached. It also displayed 0L measuring a 5V source. Both are clearly incorrect.R2) VC650 displays 0L on resistance when measuring a resistor and with probes shorted. Both are clearly incorrect.R3) The voltage reading across IN LO and IN HI is reported at 1.3mV for a 5VDC source while the lcd displays 0L. This is clearly incorrect.R4) The input impedance of the VC650 when set to DCV is reported as 7.4M or 0.9M ohm depending on which meter is used. This likely incorrect. I expected a reading like 10 or 11.11M ohm.R5) R77 in the schematic is a 10M ohm resistor and when measured out of circuit, it is 10M ohm. This is correct.I would like the results of a few more checks despite Cold-1 ordering two 7135 ICs (Note 1).15) Can you measure the voltage between pins 9 and 10 without any probes plugged in and VC650 set to DCV?16) I marked up the schematic and would like to see the voltage measurements at the following points a, b,c, d, e, f and g all with respect to ground. For this test, please set the VC650 to DCV and connect it a 3V DC source (due to Note 3). Again, please report the reading on pins 9 to 10 again for the 3V source.Note 1: When I searched yesterday on ebay, the lowest price I could find was 3.29 USD. I was surprised that Cold-1 found 2 for $5 and when I did another search today, I found the auction for $2.48 USD.Note 2: I can't find a decent picture of the VC650 or user manual so I have attached a picture of the VC670 to show it doesn't have the traditional rotary switch.http://clx.freeshell.org/pics/multimetres/voltcraft_vc670.jpghttp://translate.google.ca/translate?hl=en&sl=de&u=http://www.kappenberg.com/pages/wandler/gat073.htm&prev=searchNote3: Despite using a 4.5 digit 7135 IC, the VC650 is a 4000 count multimeter according tohttp://home.arcor.de/bernd_kunze/digiscop.htmNote 4: I finally found the original manufacturer of this multimeter despite clues in the schematic staring at me right in the face. It is a Wens 50. Wens is a Korean company.According to company history, the Wens 50 series was developed and manufactured in Oct 1998 and is CE and GS (German Standard) certified.http://www.wens.co.kr/sh_content_eng.html?page_gr=3&page_id=3http://wens.en.ec21.com/WENS_50_SERIES_Concept_Multimeter--83354_83355.html

author: Cold-1
author_rank: Contributor
timestamp: March 22, 2015, 07:45:44 am
content: Ahhhrg! Stupid me... I measured the wrong IC lane.The correct value for 3) is "160mV". For 15) it is starts at "-2mV" and goes up to "0.7mV" in a roughly 2 second time period.Also concerning Note1: I did order them from AliExpress since the cheap offers from eBay are the same Chinese merchants.Now for 16):a) 3.2Vb) 0.423Vc) 420mVd) 63mVe) 138.6mVf) 137.6mVg) = f)I don't know if it matters, but for measuring R22 (e and f) I had to remove the LCD.

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 22, 2015, 07:42:02 pm
content: Quote from: Cold-1 on March 22, 2015, 07:45:44 amNone of those readings are near what would be expected. With a 3.2V input, the voltage divider should end up in 1/10 mode. Unloaded, the voltage at point b) would be 320mV, but with loading from another 10Meg DMM, it should read about 290mV. The rest of the points all the way up to the ADC should be about the same value, maybe a little less as the series impedances add up. e) and f) are at R23 not R22.You can verify what mode the divider is in by checking U4 pins 9, 10, and 11. And verify that U4 pin 3 is really 0.0V (ground).

author: Cold-1
author_rank: Contributor
timestamp: March 23, 2015, 04:19:25 pm
content: QuoteYep, I ment R23 ;-)Pin 3 on U4 is kind of 0V, it's 0.1mV. As for Pin 9-11: only Pin 9 seams to be high (0.7V). Pins 10 and 11 are around 6mV.I have done a measurement of c) and d) again, and I realised, I got off by two pins (counting is an art...). Here are the correct values: c) = 428mV and d) = 147mVI'm starting to loose hope. Maybe it's best to just trash the thing, although it'd give me a heartbleed... (I just don't like throwing stuff away that potentially could work)

author: Lightages
author_rank: Unknown
timestamp: March 23, 2015, 06:46:52 pm
content: Quote from: Cold-1 on March 23, 2015, 04:19:25 pmIt is very commendable that you don't like to throw things away and I feel the same way. There are times though that the effort is not worth the result. In this case the result could be unreliable and if it has failed once, how will it fail the next time without warning. Could the failure the next time contribute to wrong readings which would then lead you apply the wrong voltage to a circuit, or believe you are going to be touching with safe voltages? The level of confidence you could have in the multimeter after it is fixed would be very low.I also really am impressed with the time that retiredcaps has taken to help you. There is a time to quit at some point. For $50 you can have a brand new and safer meter to work with. It will be much more reliable.I can recommend this:http://www.ebay.com/itm/Uni-T-UT139C-True-RMS-Digital-Multimeter-with-Temperature-NCV-Backlight-/171213085325

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 23, 2015, 09:05:22 pm
content: 0.7V is too low to be considered logic high for CMOS. Based on the schematic, a 000 control input for U4 would select the 40M ohms range. Not right at all. If the state of this control bus is wrong, then we're chasing wild geese with the other test points.The control bus originates from an octal latch (U2). Testing this will require testing the logic state of its outputs while selecting different functions, and trying to deduce if they're right or wrong.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 23, 2015, 10:41:26 pm
content: Quote from: Cold-1 on March 23, 2015, 04:19:25 pmI wouldn't lose hope becausea) there is a schematic - try finding that for the Fluke 87V!b) most of the parts in the multimeter are "standard" parts and easily and cheapily availablec) I still have some ideas and test points, but I can't guarantee they will work out and may lead to dead endsd) there is a bill of materials so there is no guessing as to the values and identity of potentially bad partse) it only seems hopeless because of the timezone differences and other priorities that interferePS. If you give up all hope, check how much it would send the VC 650 to USA using the lowest/cheapest cost shipping and PM me.

author: Cold-1
author_rank: Contributor
timestamp: March 24, 2015, 03:45:47 pm
content: @ModemHead:Thanx for the help. I measured U2 in the initial state (AC Volt) and then switched to DC Volt. All pins are 0V except the following:ACV: Pin 6 = 0.75V / Pin 7 = 1.36V / Pin 18 = 1.36V / Pin 19 = 0.9V / Pin 20 = 0.49VDCV: Pin 18 = 1.02V / Pin 19 = 0.74V / Pin 20 = 0.16VI also measured U1 for fun and it shows the exact same result for both modes.@retiredcaps: Thank you for the heads up and all the time you invest in this. I really appreciate it!I know what most of the parts do by them self and could replace them without a problem. But sadly, I don't know how to read schematics, so I'm totally blind in this regard :-(

author: retiredcaps
author_rank: Super Contributor
timestamp: March 24, 2015, 10:10:54 pm
content: 17) Can you provide pictures of the back of the front case where a traditional rotary switch would be? I want to see how those rubber buttons make contact to the pcb.edit: typos

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 24, 2015, 10:45:36 pm
content: Quote from: Cold-1 on March 24, 2015, 03:45:47 pmI didn't ask you to check the power rails because the processor is running, but I should have, my mistake. U2P20 is connected to Vcc and should be about 5V, but you have indicated 0.5V or less. It would be good to verify the power supply before going further.With the power off, first verify that the COM input jack is connected directly to the battery negative terminal with a continuity check. The schematic indicates that it should be. Then use the COM input jack as your ground.There are many locations on the schematic labeled "Vcc" and "Vss". There is also a rail labeled "Vcc(CPU)" which is also 5.0V, but does not get turned off by the auto-power-off feature. Try to find a convenient spot for each and measure the voltage with respect to ground. Careful with the probes not to short anything.

author: Cold-1
author_rank: Contributor
timestamp: March 25, 2015, 05:46:27 pm
content: 17) I took 2 pictures, one with the inside of the frontcover and one of the PCB without the LCD... I also marked the connectors where the front cover connects to the pcb.@ModemHead: All Vcc I measured was 0.4V exept the one for the CPU which was 5.1V. Also, the point between R10 and R11 was 5.1V. Maybe that also causes the 7135 to malfunction (the lack of voltage, I mean)?

author: retiredcaps
author_rank: Super Contributor
timestamp: March 25, 2015, 09:13:12 pm
content: 18) Can you measure the DCV on C25 (just left of VR1)? C25 is VCC.19) Can you measure the DCV on R57 (just left of VR1)? R57 is VCC (CPU).20) Can you measure the DCV on Q9 (just below on the off/on switch)? Q9 is A1015 (PNP transistor).21) Can you measure the DCV on U16 (below C25)? U16 is a 7201LU5 (5 volt regulator).edit: Attached datasheets for Q9 and U16.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 25, 2015, 09:52:55 pm
content: Quote from: Cold-1 on March 25, 2015, 05:46:27 pmThanks for the picture showing the front. Now I see how the range switch works through those pin headers.

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 25, 2015, 10:58:02 pm
content: Voltages around Q9 are especially important, check all three pins. The pinout of Q9 is emitter, collector, base (ECB) when looking at the front (the flat spot).And yes if Vcc isn't right, nothing in the front end of the meter will work.

author: Cold-1
author_rank: Contributor
timestamp: March 26, 2015, 03:59:34 am
content: Jost got up...@ModemHead & @retiredcaps:E = 5.1V (left pin)C = 0.4V (middle pin)B = 4.1V (right pin)(this would answer 20) )Now headding off to work :-/

author: retiredcaps
author_rank: Super Contributor
timestamp: March 26, 2015, 05:35:16 am
content: To Cold-1.Ignore the suggestions for testing in this reply from me. It is clear that I am incorrect in thinking how a PNP transistor works wrt to the base voltage.Focus on reply #31 by modemhead and follow his test suggestion on removing Q9.The emitter reading of 5.1V is what I would expect when connected to a working 5 voltage regulator.If, and that is a BIG if, I'm reading the schematic correctly and understand how a PNP transistor works, your readings indicate that the PNP transistor is off due to a reading of 4.1V on the base. Thus, the collector's voltage of 0.4V is what you are seeing when you measure VCC on the pcb (back on reply #25).I marked up the schematic with ECB.If the base were 0V, then the emitter current would flow through the collector.Looking at the schematic, there isn't much left to test and measure.22) Can you measure the resistance of R60? It should be around 22k ohm.23) Can you measure the resistance of R61? It should be around 22k ohm.24) Can you measure the DC voltage of Q12? C3198 is NPN transistor. Datasheet is attached.25) Can you measure the resistance of R62? It should be around 10k ohm.Note: R60, R61, R62 and Q12 are all around the on/off switch. They are all smd components. See attached picture.26) Is that bodge transistor that is attached to a pot and resistor (maybe R58?) touching R61 and/or Q12 in anyway? See attached picture.Now off to research what Auto Power Off does and some other ideas.edit: Added test point #26.

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 26, 2015, 12:21:29 pm
content: Quote from: Cold-1 on March 26, 2015, 03:59:34 amThe Vbe for Q9 is -1.0V, which means it should be turned on hard, yet Vce is -4.7V. Should be closer to -0.2V. Q9 might have failed. Also possible that there is a fault on the Vcc rail, with something drawing too much current, which might have killed Q9.I would remove Q9 and test it. Diode test, negative lead on the base, check for a normal diode drop between base/emitter, and base/collector. Should read approximately 0.7V on each junction.With Q9 removed, tack solder a 100 ohm resistor across the collector and emitter pads. That will either bring up the Vcc rail and revive the meter, or reveal an excess of current drawn on the Vcc rail.

author: Cold-1
author_rank: Contributor
timestamp: March 26, 2015, 04:48:36 pm
content: Ok, here are the measurements:18) 0.48V19) 5.1V (0.09V if measuring the opposite pin)21) GND=0V / Input=6.9V /Output=5.1V22) 746k ohm *23) 40M ohm *24) 1=0.58V / 2=0.049V / 3=0V **25) 126k ohm *26) No, there is no touching*) I didn't desolder the SMDs, so the reading could be off**) I couldn't find a datasheet for the SMD version so I measured like this (top view):(3)___(1)|___|(2)I will now desolder Q9 and test it and then try to find a 100 ohm resistor... ;-)

author: retiredcaps
author_rank: Super Contributor
timestamp: March 26, 2015, 05:00:02 pm
content: Quote from: Cold-1 on March 26, 2015, 04:48:36 pmI see my edit to reply #30 wasn't fast enough. Good thing you didn't desolder any of the SMD components because it may turn out that you didn't need to measure anything I suggested in reply #30 due to my misunderstanding how a PNP transistor works.

author: Cold-1
author_rank: Contributor
timestamp: March 26, 2015, 05:20:30 pm
content: I have taken Q9 off and measured. The 0.7V are there so I assume the part is still ok. I also put a 100 ohm resistor in place and tested the DMM, without any change. I'm gonna resolder Q9 now.

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 26, 2015, 06:25:55 pm
content: Quote from: Cold-1 on March 26, 2015, 05:20:30 pmAck! Not yet! You need to measure the voltages with 100 ohm in place to see if the voltage came up on the Vcc, and how much current it is drawing!

author: Cold-1
author_rank: Contributor
timestamp: March 26, 2015, 06:34:51 pm
content: Darn! I missed that part. Ok, I will re-desolder Q9 and re-solder the resistor. But that's for tomorrow. Have to hit the bed, was a long day.

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 26, 2015, 06:55:28 pm
content: Quote from: Cold-1 on March 26, 2015, 06:34:51 pmSorry I wasn't clear, I'm not very good at this remote diagnostic procedure stuff.You see, Q9 is just a switch that connects Vcc(CPU) to Vcc. It is normally "on", but turned off if the processor decides to activate the auto-power-off mode. It obviously isn't working, as you have 5.1V on one side and 0.4V on the other.You *could* just jumper the emitter and collector points for Q9, but I was trying to be cautious and suggest a current-limiting resistor in case there is some fault on the Vcc rail. It is possible my 100 ohm suggestion is a bit too high. In any case, measuring the voltage on either side of the temporary resistor will reveal how much current is being drawn by everything on the Vcc rail. For a battery-operated device with presumably decent battery life, I would expect the normal current to be quite low, in the single-digit mA terrritory.

author: Cold-1
author_rank: Contributor
timestamp: March 27, 2015, 06:23:35 pm
content: Ok, I measured each side:Emitter = 5.1VCollector = 0.59VI left the resistor on, just in case I have to measure other points.

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 27, 2015, 07:26:49 pm
content: Quote from: Cold-1 on March 27, 2015, 06:23:35 pmOk, (5.1 - 0.59) / 100 = 45mAThat is way too much current for a 9V powered DMM, an akaline battery would hardly last a day at that rate. Very bad news for trouble-shooting.A device or part connected to the Vcc power bus has failed and is drawing too much current. Determining which one is not easy, basically you'd have to disconnect each suspect device from its power supply one at a time, until Vcc comes back up to normal. That could involve cutting tracks, lifting pins, or removing the device altogether.It's a low-tech shotgun approach, but functional trouble-shooting isn't going to work since much of the logic in the meter is non-functional due to the lack of Vcc. There are some "tricks" like applying a 5V power supply to the rail and letting the fault manifest itself as heat (or magic smoke), thus identifying the culprit. I can't recommend it personally because I've never tried it.

author: Cold-1
author_rank: Contributor
timestamp: March 27, 2015, 07:53:00 pm
content: The PCB is a real mess (even I as noob can tell that by looking at it, the engineer that designed this probably hit the "more entropy" button in the end), thus making advanced systematic measurements very hard.So, it's probably best to salvage as much useful parts as possible and toss it?

author: retiredcaps
author_rank: Super Contributor
timestamp: March 27, 2015, 07:59:57 pm
content: Since you already ordered some 7135s, you might as well desolder the 7135 from the VC 650 and see if VCC drops to under 5mA? It is a best guess, shot-gun approach with no evidence pointing towards the 7135 as possibly the culprit, but you may get lucky?PS I have a broken multimeter here that draws 85mA. I didn't realize it at first and then noticed my fresh 9.6V battery measuring around 8.6V after 1 hour of troubleshooting. I still haven't found the current draw culprit either.

author: Cold-1
author_rank: Contributor
timestamp: March 27, 2015, 08:07:20 pm
content: Ok, thanks. I will look into this. I will also try to replace the 7145 when it arrives. Otherwise, off it goes to electronic heaven...Thanks a ton to both of you for helping and being so patient with me! ;-)RegardsPS: If I find out something or replacing the 7145 really solves the high current issue, I will report back.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 27, 2015, 08:16:52 pm
content: I have a couple of saved links on how to troubleshoot a short.The first one.http://areksnotes.blogspot.ca/2012/09/how-to-find-short-circuit-on-your-pcb.htmlThe second one.http://axotron.se/blog/multimeter-repair/

author: retiredcaps
author_rank: Super Contributor
timestamp: March 27, 2015, 08:19:05 pm
content: Quote from: Cold-1 on March 27, 2015, 08:07:20 pmActually, you want to remove the 7135 now before it arrives. Once the 7135 is removed, check the current draw. If it is the same, then the 7135 might be good. If the current draw is lower, then you know the 7135 ispossiblybad.edit: added the word possibly

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 27, 2015, 08:44:02 pm
content: Quote from: Cold-1 on March 27, 2015, 07:53:00 pmAs retiredcaps says, if you take a part off and Vcc pops back up to normal, you have nailed it. Then look for a replacement.I'd save it as a repair project for rainy days, boredom, whatever. And it's quite possible the 7135 is the culprit and you have a replacement coming, so it wouldn't hurt to give it a go. In any case, it's good practice for tech work, which is invaluable.

author: Cold-1
author_rank: Contributor
timestamp: March 27, 2015, 10:52:04 pm
content: A quick update: I desoldered the 7135 and the voltage didn't go up :-(Also, tracing the tracks is a pain. There are more through-holes than solder pins. Some tracks run on top and then go to the other side of the board on the bottom. And if that is not enough, there are several junctions underneath the components where you can't see them...

author: retiredcaps
author_rank: Super Contributor
timestamp: March 27, 2015, 11:12:22 pm
content: Since there are a number of electrolytic capacitors, I will suggest again that you have a look athttp://axotron.se/blog/multimeter-repair/especially if you have a lab power supply (which I don't).

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 27, 2015, 11:46:16 pm
content: Quote from: Cold-1 on March 27, 2015, 10:52:04 pmphooeyQuote from: Cold-1 on March 27, 2015, 10:52:04 pmYep, tracing out a PCB can be tough, especially if it's crowded like that one. A good continuity tester is handy. If you could trace out the Vcc tracks, it might be possible to rule in or out whole sections of the board by cutting the track to isolate groups of components. You can always patch it back together with a solder bridge or a bit of bare wire.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 28, 2015, 12:14:59 am
content: One thing that might help with the tracing is to take your pcb and shine a bright light from the back and take a photo of it.In this thread, I posted a picture of my UEI DM 393. It was shot with the sun shining behind it.https://www.eevblog.com/forum/repair/uei-dm393-repair-advice-all-segments-on-all-the-time/If you carefully shoot the front and back, you can then do an "overlay". I helped someone about 3 or 4 month ago and he provided overlay pictures that were excellent for troubleshooting. I can't remember that exact thread, but I will look for it.And no, I have not repaired the UEI DM 393 yet.

author: kardacz
author_rank: Contributor
timestamp: January 14, 2016, 06:18:39 pm
content: Good evening; on this same model of multimeter, the Integrated Circuit: KS57C2616 (or WENS50) should you it be programmed by software for the multimeter works

author: retiredcaps
author_rank: Super Contributor
timestamp: January 14, 2016, 06:37:33 pm
content: Quote from: kardacz on January 14, 2016, 06:18:39 pmI'm not sure what you are asking. What is not working? Can you measure a simple 9V battery?

author: kardacz
author_rank: Contributor
timestamp: January 14, 2016, 06:58:47 pm
content: Merçi have already answered. On my multimeter (vc650), the leading integrated circuitry was dead, he warmed the multimeter showed: OL and its consumption was 300 mA !! (Origin: WENS50), I was able to download the schema (even on this forum), and they put KS57C2616 .... I now put the new Integrated Circuit (I verified the magnifying lamp the state of the welds). But the problem is that it does not turn on. Therefore you must reprogram it with software, or there's some other explanation you there

author: kardacz
author_rank: Contributor
timestamp: January 15, 2016, 05:12:20 pm
content: oops! Nobody has the answer ??

author: kardacz
author_rank: Contributor
timestamp: October 25, 2016, 12:22:06 pm
content: Hello; replace 2 Integrated Circuits NJU4066 because the fuse has not played its role (rolled aluminum), and these components are destroyed!