MeterMan 37XR "no digits" - Page 1
Forum section: electronics / repair

author: HummingBird
author_rank: Contributor
timestamp: July 06, 2016, 07:17:40 pm
content: Hello,I got an MM 37XR which shows no of the 7 segment digits when turned on. Symbols are changing when you change the measurement option, so display is OK. Buttons are reacting, in MIN/MAX you see all the digits reading 00.00...so they are also OK - anybody some ideas how it is "blank" on startup? ADC broken? Or...?Thx in advance for any help, Klaus.

author: retiredcaps
author_rank: Super Contributor
timestamp: July 06, 2016, 10:18:08 pm
content: If you haven't tried a fresh battery, please try that. Post clear focused pictures of both sides of the pcb so we can see the inside.Did you purchase this meter new or used?

author: HummingBird
author_rank: Contributor
timestamp: July 08, 2016, 08:51:58 am
content: It was a "present", because ist broken...I dont know anything about how it got broken. All parts are looking good, no traces of fumes or sth elseBut I guess thats a very specific Problem so also without any circuit diagram or anybody who repaired exactly the same issue ist some Kind of unrealistic...but there is still some hope left

author: SteveyG
author_rank: Unknown
timestamp: July 08, 2016, 09:29:09 am
content: Worth checking the zebra strip on the LCD?

author: HummingBird
author_rank: Contributor
timestamp: July 08, 2016, 09:31:00 am
content: ...nope, as all Digits are working in MIN/MAX but showing 00.00Ist no technical Problem of the uC or the Display. Its sth else...

author: Kleinstein
author_rank: Super Contributor
timestamp: July 08, 2016, 11:51:49 am
content: The blank display could be a way to show overload, though not the best. The fuses for the current ranges are missing, so current measurement will not work, but should still read 0.000 . So looks like broken and hard to repair.For such metes there usually is no schematics available and much of the functions is inside one of the big chips. So unless something obvious near the input, it is hard to impossible to repair.One thing one could check is, if there is a reasonable current flowing when in Ohms mode or diode test. Continuity test (beep) might work independent of the display and adc, so it could be still working.

author: HummingBird
author_rank: Contributor
timestamp: July 08, 2016, 07:17:01 pm
content: Hmmmpf...I guess you are right but I dont want to accept. 0Ohm Tester is also not working, but it detects "wrong plugs" by beeping. Overload is normally "OL"...I think it is really broken and cant be repaired. I will put the PCB in stock and thats it...Thx!

author: retiredcaps
author_rank: Super Contributor
timestamp: July 08, 2016, 08:25:24 pm
content: I'm having a difficult time following your abbreviations and description of the problem. Let's get a baseline.Q1) Without any probes plugged in, what does DCV show?Q2) Without any probes plugged in, what does ohm show?Q3) Without any probes plugged in, what does ACV show?Q4) Plug in your probes and short them, what does ohms show?Q5) Measure a 1k ohm resistor, what is the reading?Q6) Measure an 1.5V AA cell, what is the reading?

author: HummingBird
author_rank: Contributor
timestamp: July 09, 2016, 09:02:14 am
content: 1) all symbols as selected measurement (Ohm, mA, A, V...) but no 7 segment digits (blank)2) see 13) see 14) nothing, still blank, beeper does also not work5) see 46) see 4But if you select MIN/MAX, you read 00.00, so the digits themself and the µC are not the problem...Thx a lot for your patience but as I have "some more DMMs" its not important to reactivate that one, anyway its an TrueRMS which would have been missing in my equipment...Klaus.

author: lowimpedance
author_rank: Super Contributor
timestamp: July 09, 2016, 11:00:31 am
content: Just curious , are you able to check that both crystals are oscillating?, well the one with the micro controlling the lcd is but what about the other?. Reason for the rather odd question is because I fixed an old 'Escort' branded meter that had the TC820 a/d converter chip oscillator stop working and the result was no 7 segment digits displayed!. But the LCD micro was still working. Similar sounding symptoms to what you have with your meter.(Just noted also in the photo that yours has two crystals!! just like the old Escort).

author: HummingBird
author_rank: Contributor
timestamp: July 09, 2016, 09:21:11 pm
content: ...funny, I was thinking about testing the same - but I thought: Nooo way, that completely unlikely. But, now I WILL test itI think too that the ADC is the problem.Thx, Klaus.

author: HummingBird
author_rank: Contributor
timestamp: July 13, 2016, 04:43:41 pm
content: HEUREKA, lowimpedance! That was it! The osci of the ADC was broken, 1.23V cont level measured...I changed it - works! F*cking perfect, thx for persuading me that its worth testing it!Best regards, HB!

author: retiredcaps
author_rank: Super Contributor
timestamp: July 14, 2016, 04:54:04 am
content: @ lowimpedance.

author: PatrickWang1
author_rank: Newbie
timestamp: May 12, 2020, 09:30:26 am
content: Hi HummingBird,I got the same issue like your 37XR.My broken one is the X1 crystal, May I ask your advice on what is this XTAL PN, or its frequency?Thank you! Wish you a great day!Best,Patrick

author: PatrickWang1
author_rank: Newbie
timestamp: May 13, 2020, 03:47:04 am
content: Hi HummingBird and All,Turns out I found the DAC datasheet on-line.It should be using a 4MHz crystal.https://www.alldatasheet.com/view.jsp?Searchword=Es51966&gclid=CjwKCAjwkun1BRAIEiwA2mJRWWvuQFYGRsBzg8vyyc5aOX3QWebapBazKMCa8l4U4_M5JDGh2bHqsBoCp9MQAvD_BwEBest,Patrick

author: rph-r
author_rank: Newbie
timestamp: April 28, 2021, 10:59:44 pm
content: Same diagnostic, same cure!I was about to throw it when I found this post.You made me save n-hundred $ and keep an old friend of my electronics adventures... so THANK YOU!