repair a digital oscilloscope? naive? - Page 1
Forum section: electronics / repair

author: kinylc
author_rank: Newbie
timestamp: December 24, 2012, 02:13:57 am
content: Hi guys,i bought an old digital scope (YOKOGAWA DL1540) few days ago, it had some problem (calibrate error No.719, missing trace and one reading are out of scale) with it, is that possible for people like me(i have a multi meter, some screw driver), to repair it my own without much electronic knowledge?

author: tinhead
author_rank: Super Contributor
timestamp: December 24, 2012, 02:33:04 am
content: Quote from: kinylc on December 24, 2012, 02:13:57 amhow much did you paid? Not that i would buy it, this is 200MS/s DSO only (even if a really cool one, the termal printer and GPIB)This means for single shot capture that 10MHz square signal you can measure max. ,repetetive signals of course you can go up to 150MHz.Quote from: kinylc on December 24, 2012, 02:13:57 amhmm, Analog Board or Attenuator Assembly broken. This can -with some luck - be easy to fix,but it can be as well disaster. Check for obvious (visual) things on these both boards (which they are you can find out by looking on the service manual in below)Quote from: kinylc on December 24, 2012, 02:13:57 amehm, short answer "no" - but on the other side who knows ...The problem with Yokogawa is leak of schematics or calibration apps necessary to run calibration.There are some information available, check them, maybe it will help you a bit:http://labit501.upct.es/~fburrull/docencia/FundamentosTelematica/OsciloscopioDL1520/but normally, unless there is something really obvious broken like a plug, trace broken etc., you willnot manage to fix a Yokogawa gear.

author: kinylc
author_rank: Newbie
timestamp: December 24, 2012, 03:11:46 am
content: the did seller offer me a kenwood 20mhz analog 4025 for USD80, but i tot a digital one always better, so i paid about USD200 for this one, i dont really know the sample thing(and the problem it came with), really thank you for the link, so do u still recommend i take it apart? is it worth to repair? or i should just sell it on ebay?

author: c4757p
author_rank: Super Contributor
timestamp: December 24, 2012, 03:29:18 am
content: I wouldnotbuy a 20 MHz scope for US $80. I had one in absolutely perfect condition, nicely calibrated to enough precision that you can't make out any error, and I clearly demonstrated every aspect of its perfection. Try as I might, I was not able to even get interest in it, let alone sell it, until I dropped the price to $50. 20 MHz two-channel is the bare minimum.Not sure I'd say a 150 MHz digital with known problems is worth $200, though the four channels might make it worth that. I buy used analog scopes all the time to fix them, but I've never ventured into the world of digital scope repair so I have no clue what they sell for. Analog ones can be hard enough.

author: rsjsouza
author_rank: Super Contributor
timestamp: December 24, 2012, 03:35:59 am
content: Hi,I can't help you much with the Yokogawa, but if you are considering buying the Kenwood I have it and can say it is a really nice oscilloscope - not sure if the price is right, but if it is working and is within your budget...This analog scope has been serving me very well for the last 18 years and it is very useful for the vast majority of my applications. I just went digital last year (a Rigol DS1102E) due to the need for the storage functionality. Obviously digital oscilloscopes have several useful aspects (more precise voltage and frequency measurements, one-shot triggering, etc.) but the analog scope is perfect for learning electronics and doing small repairs. In this case, the difference in cost is very good.If you are feeling brave to venture inside the oscilloscope, I did a search (and ended up finding the link sent before) with a nice service manual for the DL1500 series of Yokogawa oscilloscopes.

author: kinylc
author_rank: Newbie
timestamp: December 24, 2012, 04:00:00 am
content: The self-test shown everything ok but the calibrate error code No.719 is there, thanks to tinhead's service manual suggest att assembly, analog board may have problem. i think i will tear it apart, later.

author: tinhead
author_rank: Super Contributor
timestamp: December 24, 2012, 09:15:47 am
content: this means the part of analog board which can be checked (like 50% of ADC ICs) could be ok. Maybe simplerelais locked, this would match the attenuator and calibration error and make sense with "pass selftest" message.200$ is a lot of money, but yeah, it does have nice triggers, 4 ch, gpib, etc, and depends on your luck maybe evenI2C protocol option? Anyway, it's might be a win situation if the issue is only relais based.

author: kinylc
author_rank: Newbie
timestamp: December 26, 2012, 04:45:12 pm
content: pretty sure its not relay related problem, when i switch ac dc coupling they do fine, also tried switching voltage and time. turning those pots on the analog board and att board are not helping, what else i should be looking at? any suggestion?

author: free_electron
author_rank: Super Contributor
timestamp: December 26, 2012, 05:23:54 pm
content: Quote from: kinylc on December 26, 2012, 04:45:12 pmwhy is it that anyone with zero knowledge always begins by turning anything that looks like a potmeter, trimcap, or inductor ?The first rule of repair is : DO NOT ATTEMPT TO ADJUST ANYTHING !the second rules is : if you do not know what a trimmer does : DO NOT TOUCH ITmy speculation is the proble sits in the metal can. probbly an input attenuator relay stuck.

author: tinhead
author_rank: Super Contributor
timestamp: December 26, 2012, 05:56:57 pm
content: Quote from: free_electron on December 26, 2012, 05:23:54 pmyeah, this is always very unfortunate.People even don't know what kind of mess they doing, it's actualy better to unsolder BGA chip and resolder it 10 times in adiy oven than "playing with trimcaps or pots" - once they set wrong in most case you can only re-calibrate the device with special hardware and software.Quote from: kinylc on December 26, 2012, 04:45:12 pmremve the metal cover, the small board is attenuator unit. The error will be probably somewhere there.Check voltages (maybe attenuator switch driver is broken), check relais (apply 1khz signal to working channel, set a specific condition, measure, write down,do the same with broken channel and compare results ...) - when there is no diff in the signals then check the bigger (the analog board), e.g.if the signal is going to ADCs.Btw, you have working channels in this scope, use them! When you apply 1khz square to ch1, you can meaure e.g. ch3 and compare with the broken ch4.

author: kinylc
author_rank: Newbie
timestamp: December 28, 2012, 06:02:35 pm
content: i found the problem(broken resistor) of the ch4, after i fix it, put them back togather. the next morning it was all ok, all 4 channel (ch2 and 4 is out, like they said, i shouldnt touch those trimpot). late night when i turn it on, traces become funny again, i tear them apart, checking the board by apply pressure to the analog board, the trace go up and down vertically (sometime unscrew/screw one or two will help) what can i do next? PLEASE HELP!

author: Unknown
author_rank: Unknown
timestamp: December 29, 2012, 02:12:08 am
content: I would look for broken traces on the circuit, probably in the area of the dead resistor: it's quite rare for a resistor to die in the absence of extreme overload or physical abuse. My guess is that pressure on the PCB, for example due to the scope being dropped, damaged both the resistor and the PCB. Flexing of the PCB, by loosening/fastening screws, could intermittently break/restore contact in the broken trace/plated hole. This could be fun since the PCB will likely have 4+ layers. Mike's video on the fireman thermal camera repair (search for mikeselectricstuff on Youtube) might be instructive, since this turned out to be a similar issue.

author: kinylc
author_rank: Newbie
timestamp: January 03, 2013, 12:39:08 pm
content: i dont know, i assemble it back then it work all ok now, thanks for the help and lesson.

author: gaborgabor
author_rank: Newbie
timestamp: November 06, 2020, 01:52:25 pm
content: Hi ! Can you help me ? I have a Yokogawa DL1540CL oscilloscope. The CH1 and CH3 is good , but the CH2 and CH4 have a vertical noise. ( look the pictures )What might be the problem ? Where do I search it ?Thank you for your help.

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 07, 2020, 09:40:02 am
content: Look around acquisition RAM.

author: gaborgabor
author_rank: Newbie
timestamp: November 10, 2020, 12:10:19 pm
content: Dear Shakalnokturn,thanks for the reply.I don't have a wiring diagram.Can you send it ?Or where can i find the acquisition RAM in the scope ?Thank you.

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 10, 2020, 11:03:03 pm
content: I don't have the schematic either, I don't think there are any available, you could try asking Yokogawa themselves.This may help as there are a few details on what does what even if it isn't the same scope:https://www.eevblog.com/forum/testgear/yokogawa-dl1740-oscilloscope-repair-teardown/The general flow from the BNC in most DSO's (of that era) is:Coupling / BWL relays, signal conditioning (attenuation/amplification the signal goes differential from here and branches out to ADC and trigger circuitry), ADC (from one to four depending on sample rates of input channel and ADCs used), data DEMUX (interleaves the data from the ADCs to fast SRAM, interleaving was necessary because access time was still too slow for the data rate to be handled by a single SRAM).To complicate things a little some models allow to combine acquisition channels when using only 1/4 or 2/4 channels to gain in sample rate and memory depth.A few things to try to narrow the symptoms if these are possible on your scope:Change gain and offset.Change sample rate (timebase).Change memory depth.

author: nctnico
author_rank: Super Contributor
timestamp: November 13, 2020, 10:25:17 am
content: This can also be a problem in the ADCs themselves. To test you have to use a triangular wave at several frequencies, amplitudes and DC offsets in order to which bits go wrong. Diagnosing this problem requires some understanding on how ADCs work. Note how my DL1740 had a similar problem where 1 bit was wrong on one channel. I never managed to trace it down to a cause though although I strongly suspect it was the ADC in my case.Another option is to swap the ADC between channel 1 and 2 for example and see if the problem moves along but this requires good reworking skills.

author: gaborgabor
author_rank: Newbie
timestamp: November 13, 2020, 10:50:14 pm
content: Thank you for your help Shakalnokturn and Nctnico !