Uni-Trend 2102 CEL Oscilloscope Repair - Page 1
Forum section: electronics / repair

author: Anoop
author_rank: Newbie
timestamp: October 31, 2013, 02:44:22 pm
content: Hi Everyone,I'm hoping someone can assist me with the following:I have a Uni-Trend 2102 CEL Oscilloscope which I have not used very much yet, but has now stopped working. It was fine while I was using it a few days ago, and I switched it off to do something else. Around 15 to 30 minutes later I reached out to switch it on again and was surprised to find that the top switch was still in the "on" position, but the unit was (or appeared to be) completely switched "off".Pressing the switch off and on again had no effect, not even the fan was turning, no power up at all. I checked the internal fuse, and this was fine.I did a simple teardown, and pictures are below:From the symptoms I suspect (and hope!) that the problem is just in the power board. I've sent a number of messages to Uni-Trend in both Shanghai and Hong Kong asking for a)Service manual and/or b)Quote for new power board. However as yet have no reply.so I removed this from the unit to start testing. I found a schematic for the Rigol DS1052 power supply which had been made by a kind contributor from your forum, A Hellene. I also found on the net a service manual for the Siglent SDS1000 series. While both of these seemed to match with each other, they unfortunately did not match with my Uni-Trend power board as the voltage pin-out configuration of the twelve pcb landings for the connector on the Uni-Trend was quite different. In most other respects the board is very similar. As yet am not able to find any service info or schematics for this specific board, and do not know whether the manufacturer is going to reply.Referring to the pictures:- Input voltage: 240 V- DC Voltage across capacitor "A" after rectification: 350V aprox- Item "B" is a 3-pin "TOP Switch" PWM switcher, part no. TOP225Y- Item "C" is a transformer with 5 pins on each side (total 10 pins)- On the picture of the back of the pcb, showing the landings, the two circles for item "C" are the pins for, what I have ASSUMED to be, the primary of the transformer.- There is no voltage reading across these two pins at "C".- Between lower circled pin of Transformer "C" and Source pin of TOPswitch "B" there is aprox 350V DCIt would seem that there is a problem with the TOPswitch and that no current is able to pass between its Drain and Source Pins. I will try replacing this part - I am waiting for part to arrive. Another thing - the two pins which I have assumed are the primary coil of the transformer - have an impedance of only around 1 ohm (measured while in-circuit). Does this seem reasonable? I am not an expert so any suggestions would be appreciated relating to repair, obtaining service manual or schematic, or even a source for a replacement board, anything!I'd noticed a lot of postings on this forum regarding these Chinese manufactured DSO's, and so hope that one of you experts is able to assist!Thanks people.Anoop

author: dr_p
author_rank: Frequent Contributor
timestamp: October 31, 2013, 03:06:11 pm
content: the fuse is fine, so the rectifier and transistor(item "B") are fine (not shorted). Is there any voltage on the output ribbon cable?

author: Anoop
author_rank: Newbie
timestamp: October 31, 2013, 04:47:05 pm
content: Hi Dr_p,There's no voltage at the ribbon cable. The voltage stops at item "B". Nothing coming out of the transformer secondaries.rgdsAnoop

author: DL8RI
author_rank: Regular Contributor
timestamp: October 31, 2013, 05:14:27 pm
content: These TNYXX (your "B") die rather often after a few years. Not with a short but they just stop working, had this issue with a TNY266PN just a few months ago. I'm pretty sure after replacing it your scope should work again.

author: Anoop
author_rank: Newbie
timestamp: November 01, 2013, 05:14:38 pm
content: Quote from: DL8RI on October 31, 2013, 05:14:27 pmHi DL8RI,Thanks! Hope you're right!

author: TheManual
author_rank: Newbie
timestamp: January 27, 2015, 10:21:59 pm
content: I have the same oscilloscope utd2102cel. The problem lies in the fact that one channel has breakdowned (presumably by static electricity). When testing with the rectangular pulse (internal oscillator) it shows wrong fronts and amplitude. Please advise,how the problem can be solved?

author: tautech
author_rank: Super Contributor
timestamp: January 27, 2015, 10:33:59 pm
content: Quote from: TheManual on January 27, 2015, 10:21:59 pmWelcome to the forum.Static should not harm the inputs.Post a picture so we know exactly what you see.

author: TheManual
author_rank: Newbie
timestamp: January 29, 2015, 07:13:40 pm
content: Here are the pictures of signal.The signal from the internal oscillator is applied to both channels of a single probe using a splitter (tee).The is a second question. At what points on the circuit board tha battery can be connected (eg 12 volts)

author: tautech
author_rank: Super Contributor
timestamp: January 29, 2015, 07:30:07 pm
content: Looks like the input settings for Ch 2 are for a 10x probe.Is this the case?Are you wanting to battery power this DSO?

author: TheManual
author_rank: Newbie
timestamp: January 29, 2015, 09:54:02 pm
content: It is seen not rectangular pulse on ch1(blue). CH1 signal drifts slowly across the screen up and down. I used only one probe with 1x on its holder. Both settings of channels are 1x also.Is's known exactly that ch1 is broken after the experiment with high voltage.I plan to use the battery as galvanic separation.And also 3 questions that appeared after viewing this forum:1) Is it possible to program the oscilloscope by the usb port (commands and accessed through a C ++ program). Is there a driver or compability with Tektronix (or Rigol)? Where I can find some examples?2) I've Seen on the forum topic about the expansion of the range (https://www.eevblog.com/forum/testgear/hantek-tekway-dso-hack-get-200mhz-bw-for-free/).Is it possible to apply to this oscilloscope?3) Some oddities with formats seen. The oscilloscope has the ability to save two types of files: .sav (longer) and .dat.Tried to read information directly from these files.After researching (hex editor) is established:data from both channels is recorded to .SAV-file (does not depend which channel to select from the menu of oscilloscope) and .DAT contains only one channel(the one that has been selected in the oscilloscope menu). Thus, the selected channel is recorded in the file 2 times, and not equally.It was able to recognize the structure of .sav and .dat.Strange that ch1 (for .sav) contains 6000 counts and channel2 - 6324.

author: tautech
author_rank: Super Contributor
timestamp: January 29, 2015, 10:20:08 pm
content: Quote from: TheManual on January 29, 2015, 09:54:02 pmOk so the DSO might have had an over-voltage event.Also check your BNC cables for continuity just to eliminate them as a problem.If it all checks ok, Ch1 might be damaged.You might need to follow the signal path with another scope if you can't find any damaged/faulty components with a DMM.QuoteDo you mean isolation for prevention of GND loops?