VOLTCRAFT MT-51 - Page 1
Forum section: electronics / repair

author: lionelkjh
author_rank: Frequent Contributor
timestamp: November 13, 2018, 12:05:40 pm
content: Hello everyone! I am looking for the frequency value of a defective quartz on a VOLTCRAFT MT-51 multimeter, the frequency is not registered, and nothing is written on the card. Can someone help me ?? I attach the photographs of the multimeter and the quartz model that it is. Thank you in advance for your help!

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 13, 2018, 12:20:07 pm
content: Averywild guess would be 4MHz but maybe you could tell us the I.C. it connects to and get a more educated guess.

author: lionelkjh
author_rank: Frequent Contributor
timestamp: November 13, 2018, 12:31:51 pm
content: The integrated display circuit is a chip on board, so impossible to give you the model!

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 13, 2018, 07:49:52 pm
content: Nice to know, that's a model I'll avoid if I'm tempted.If no luck at 4MHz you could feed it with an external function generator until you find a close enough frequency.Depending on watchdogs and reset circuitry it could take some power cycling.Once you have some display find the precise frequency by using Hz function on the DMM and feeding it a known reference.How's that lab of yours filling?

author: retiredcaps
author_rank: Super Contributor
timestamp: November 13, 2018, 08:55:53 pm
content: Your meter is likely an OEM of CEM Instruments. Look at their website and see if you can find out more wrt to what IC is used and teardown pictures.

author: lionelkjh
author_rank: Frequent Contributor
timestamp: November 14, 2018, 09:32:50 am
content: Hello everyone! I tried with a frequency generator and no start found! I tried with 4MHZ, 32.768KHZ, and other frequencies, but I still have nothing; I changed the output amplitude; Nothing has changed! I have isolated the quartz with several different montages, and it does not oscillate! No inscription on the frequency above. I attach the photo of this mysterious quartz (it is very small) ....

author: lionelkjh
author_rank: Frequent Contributor
timestamp: November 15, 2018, 03:58:57 pm
content: Good evening; I really need your help: an idea

author: RobertPS
author_rank: Contributor
timestamp: November 15, 2018, 04:44:35 pm
content: Maybe this helps:The multimeter is an OEM CEM model. It seems to be the same as the CEM DT-61 or the Peaktech 3690.

author: CJay
author_rank: Super Contributor
timestamp: November 15, 2018, 05:02:30 pm
content: I think the smaller crystals have some 'odd' drive requirements and can fail to start in unsuitable oscillator circuits.That it doesn't start in circuit and you can't get the meter to 'run' with an external oscillator makes me think it's a bit more serious than the crystal.

author: lionelkjh
author_rank: Frequent Contributor
timestamp: November 15, 2018, 06:32:07 pm
content: Good evening; very good, it's nice to have answered! What he was good at; it is to have the schema of one of these multimeter to have the frequency of the quartz that I seek: it is certainly the most difficult ..... Would anyone have it

author: lionelkjh
author_rank: Frequent Contributor
timestamp: November 15, 2018, 06:40:11 pm
content: I just found the picture of a DT-61 disassembled; looking at the picture, we can see the small quartz detected XT2

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 15, 2018, 09:33:06 pm
content: It is hard enough to find schematics for real multimeters.

author: lionelkjh
author_rank: Frequent Contributor
timestamp: November 17, 2018, 08:43:19 am
content: Hello; if someone owns CEM DT-61 or PEAKTECH 3690, he might be able to give me the reference marked on quartz; or with an oscilloscope having a large input impedance to deduce the clock frequency: for the moment; I did not find a schema!

author: lionelkjh
author_rank: Frequent Contributor
timestamp: November 20, 2018, 07:10:31 am
content: HELP!

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 23, 2018, 06:44:52 pm
content: Sell it off as if you didn't know how to test it or you never attempted to repair it.I'm sure you'll find some "pigeon"!Sorry for my french

author: lionelkjh
author_rank: Frequent Contributor
timestamp: November 24, 2018, 04:52:25 pm
content: stop drinking shakalnokturn!

author: ElecSeb
author_rank: Regular Contributor
timestamp: November 24, 2018, 05:08:33 pm
content: How dd you test for a defect crystal?You could try to build the cricuit from this radio engineer:https://www.qsl.net/g3pto/xtest.htmlAnd following measure with a frequency counter. This way you know for sure the crystal is working or NOT AND of course you are now the proud owner of the correct frequency needed for this DMM (which we of course would like to know as well).If it is really defect, then you have a problem.If it is not defect, you have to search for other factors on the board which make your DMM not start!