Aron BS-601 Oscilloscope vertical  amp issue (FIXED) - Page 1
Forum section: electronics / repair

author: The_Todd
author_rank: Regular Contributor
timestamp: January 27, 2019, 04:47:33 am
content: Hello guys,im trying to fix a Aron BS-601 scope but the issue im having is the vertial part is not worki ng properly, whatever signal you put in ans whatecer setting you use the trace is always very thin and flat.the problem is the the vertical amp, its only pumpi g out about 12v to the scope with of couse needs to be much more. ive attached the circuit that im refring to, the circuit has all the corect voltages going ito it and q19 nd q20 also have the 120v sitting behind it.however about 12v is geting to the outputsThe exact way this circuit works is a bit beyond my capa bilities but if i coukf get any help it wold be appreciated.Sent from my iPad using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: January 27, 2019, 04:51:48 am
content: Could it be a simple severe case of contact tarnished. Have you tried cleaning the contacts?Watch the video;

author: The_Todd
author_rank: Regular Contributor
timestamp: January 27, 2019, 04:53:25 am
content: Yup tried that. And the signal is dull overall. No matter how much i fiddle with the switchesSent from my iPad using Tapatalk

author: tautech
author_rank: Super Contributor
timestamp: January 27, 2019, 10:39:09 am
content: With zero signal and V position centered each plate should see ~60V.The 120V is supplied to the final output amps via a current limiting resistor so down stream from that check for componentry failed short that might effect both plates.Things like C38.

author: The_Todd
author_rank: Regular Contributor
timestamp: January 27, 2019, 12:45:36 pm
content: Quote from: tautech on January 27, 2019, 10:39:09 amOh that makes sense il checkit tkmmorrowCheersSent from my iPad using Tapatalk

author: tautech
author_rank: Super Contributor
timestamp: January 27, 2019, 09:10:27 pm
content: You might also spend a little time studying this, it can be very helpful in pointing you in the right direction:http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

author: Armadillo
author_rank: Super Contributor
timestamp: January 27, 2019, 10:10:58 pm
content: Hi, I see that you can probe around powered on, so you know well the safety aspect.Aside from the multimeter, what other kinds of testing instruments or component testers do you have?

author: The_Todd
author_rank: Regular Contributor
timestamp: January 27, 2019, 11:11:41 pm
content: I have all the Main tool, incuding a working scope and microscpe.Sent from my iPad using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 12:57:42 am
content: Here is a pic of the signal the best i can get it, thisis a .5v test signalSent from my iPad using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 03:14:01 am
content: You have a handful of equipment there.The test signal, what was the volt/div you used and was the probe set to Divide by 10 setting?If you set the volt/div to lowest 10mv/div any change?If you switch your probe to Divide by 1 any change?

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 03:27:55 am
content: Quote from: Armadillo on January 28, 2019, 03:14:01 amyeah just few thingthe probe is on 1xand no mater what there is little difference. it will go anywhere from a dead straight line to a small signalabout 1cm in hight. and that it. ive tried every setting and different probes and bot sides are the same.

author: tautech
author_rank: Super Contributor
timestamp: January 28, 2019, 03:57:29 am
content: By any chance are the red knobs on the V/div not clicked home in the Cal position ?

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 04:19:35 am
content: We have tried the easy ones, now the harder part [your choice, up to you if you want to do it, considering the age of this scope];Please be careful, observe safety.Use a working scope, set to AC, probe Divide by 10, Volt/Div as appropriate;The scope under repair, set to 10mv/div, apply test signal into the input.Probe with respect to GND, [if you are save the traces, please post it up]Collector Q5, then Collector Q6,Collector Q9, then Collector Q10Emitter Q13, then Emitter Q14Volt meter measure Voltage at Cathode of D10 and then Anode D14 with respect to GND.[You sure you have checked the 5V, 12V and 20V?]The above just merely divide the areas of search.I suspect one of the common biases is OUT.

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 04:27:11 am
content: Quote from: Armadillo on January 28, 2019, 04:19:35 amOh this is detailed thank you, my other scope is analog too, so ill try and try and get photos.with the ground isolation, i haven't got an isolation transformer, so should it be ok without itor should I detach the ground odd the faulty scope of the scope used for testing? (and yes, all equipmenti use is going thought a safety switch designed for testing equipment)thank you again,for you help.

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 04:35:41 am
content: Your scope is powered by isolation transformer already.I only assumed here the isolation transformer is working fine, otherwise use a isolation transformer to be safer.Just don't, NEVER probe beyond the isolation points like probe the mains....

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 05:07:41 am
content: Don't know if your schematic is updated, the old one has 2 Q4 there;Anyway, see attached.You start with mid point pairs. if no signal despite lowest V/div, you forget downstream points, always move upstream.Conversely if there are signal, then move downstream mid points and repeat same procedure. Divide by 2, Divide by 2.... got the idea.?That will cut measurement points down a lot.Hope you understand this short English.

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 05:29:06 am
content: Quote from: Armadillo on January 28, 2019, 04:19:35 amOk let’s star with Q5 collectorSent from my iPhone using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 05:32:48 am
content: Q6 collectorSent from my iPhone using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 05:34:06 am
content: Q9 collector takeNote I had to advise DIV to 50mvAlso q9 looks like it had been replaced recentlySent from my iPhone using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 05:37:21 am
content: Q10 collectorSent from my iPhone using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 05:42:11 am
content: Q13 emitterSent from my iPhone using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 05:42:55 am
content: Q14 emitterSent from my iPhone using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 05:56:43 am
content: Quote from: Armadillo on January 28, 2019, 05:07:41 amHmmmm im a bit confused. im sure the signals getting through to the end but its just not strong enough, seeing as both outputs are the same could it be assumed there is a mutal fault thats dragging down both sides?Sent from my iPad using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 06:02:39 am
content: Let's persist on until we conclude to the deflection plates;Volt meter measure all the Base Collector Emitter Voltages of the followings Transistors with respect to GND;Q15 Base = VCollector = VEmiter = VUntil Transistor Q24.

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 06:03:34 am
content: Also seing the jump in voltage from the first and second pair of transistors , One would assume the signal is amplifying correctly ?Sent from my iPad using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 06:07:47 am
content: Yes, I assume you probe is at Divide by 10;Those are under low voltage 5 or 12 V supply, don't expect 120V reading.

author: ZayneTech
author_rank: Contributor
timestamp: January 28, 2019, 06:32:04 am
content: How did this happen in the first place?

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 06:33:18 am
content: Quote from: Armadillo on January 28, 2019, 06:02:39 amWow, well all right then, just to clarify these are off a standard multimeter ...(The Dave multimeter no less ) This is part 1, Q19 and Q20 seem odd...... Also ive just noticed thAt most of these transistors have either been replaced or reflowed, so im guessi g he last person couldnt fix it either.q15B= 11.62VC= 11.7VE= 12.2VQ16B= 11.62VC= 11.7VE= 12.2VQ17B= 11.67VC= 11.62VE= 11.96VQ18B= 11.7VC= 11.62VE= 11.93VQ19B= 116.8VC= 117.1VE= 11.97VQ20B= 116.7VC= 117.1VE= 11.93VSent from my iPad using Tapatalk

author: tautech
author_rank: Super Contributor
timestamp: January 28, 2019, 06:38:45 am
content: Quote from: The_Todd on January 28, 2019, 06:33:18 amWarning, engage full detective mode !Consider anything and everything could be in error.Take nothing for granted and check every part/area previously worked on could be hiding some poor workmanship and/or use of incorrect parts.Keep eyes wide open for errors.

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 06:43:16 am
content: Ok and part 2Q21B= 11.44VC= 5.9VE= 12.15VQ22B= 11.29VC= 6.0VE= 12.02VQ23B= 116.5VC= 120.3VE= 116.3VQ24B= 116.5VC= 120.3VE= 116.3V*Takes a small drink*Sent from my iPad using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 06:43:26 am
content: Yep, because the downstream measured correctly, I assume he probe wrong point, so I ignore it for the moment.@Todd; still missing some Transistors not measured. I can see at VR6 the 120V disappeared....but until you finished measurement then we conclude.

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 06:45:14 am
content: Check VR6 voltages;

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 06:48:21 am
content: Quote from: ZayneTech on January 28, 2019, 06:32:04 amBecause university.I actually got a few of these all simular problems, these were used at the university, some idiot probably tried connecting it to 240v or somthing, somone else tried to fix it and ecetually got throen out. its not even about havinf a fixed product in the end (although it is nice as i hate waste) but about fixing the issue and learning how.some people like tradional 1000 pieces puzzles, I like my puzzles 240VSent from my iPad using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 06:51:15 am
content: Check this 3 components;Also check VR6

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 06:51:34 am
content: Quote from: tautech on January 28, 2019, 06:38:45 amOh yes I went full picachu on this, testing every knob and switch, resolder any dry joints, push and pull Dave style random partsof the PCB looking for any change. and visual clues where little plebs have tried to fix things before, but no, thisis a hunt the faulty componet game.Sent from my iPad using Tapatalk

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 07:08:17 am
content: Quote from: Armadillo on January 28, 2019, 06:51:15 amYes i thought this may be the issue, i thought the diode was pullj g down the voltage..... But here is the detailsthe voltage in the centerpoint is 11.56vvoltage other side of d10 12.23vVoltage other side of r80 116.8v (yes thats corect)Diode reading of D10 in circuit0.672 and reversed 2.22Resistor reading of r80 in circuit (This is interesting)0L one way and 22M ohms with probes swapped overDoth we have an open resistor?Sent from my iPad using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 07:10:19 am
content: Take those out of circuit and measure;Remnant current may play wonders with your meter.Also the capacitor.

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 07:12:14 am
content: Most likely you found the fault;

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 07:16:01 am
content: Don't miss out VR6, just check it for added assurance.

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 07:36:34 am
content: Quote from: Armadillo on January 28, 2019, 07:10:19 amEUREKA!!!! Found the problem!!! R80 was an open line! replaced with 43k and well, now we have full range on vertical, ...however there are no Rising or falling lines, is this a calibration issue or sothing else faulty?Sent from my iPad using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 07:42:04 am
content: Turns out, a cheap Resistor... ahahahahahaAs I have long suspected, a common bias issue.Regarding the vertical lines,,,,, assume you have super fast rise and fall time, so fast you cannot see it..... joking...try adjusting the focus and brightness control. Cheers!Quote from: Armadillo on January 28, 2019, 04:19:35 am

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 07:51:30 am
content: Quote from: Armadillo on January 28, 2019, 07:42:04 amJust went through all the knobs, and both sides same isue. hmmmm so is this a fault, a calibration issue, and if so cabration on witch board, power supply, vertical or time?Sent from my iPad using Tapatalk

author: Armadillo
author_rank: Super Contributor
timestamp: January 28, 2019, 07:54:53 am
content: You mean the Rise and Fall vertical lines..... I don't think is a fault... is normal to me... this is not a DSO scope...You imagine the lines are there....Or use a Sine Wave to enjoy.

author: The_Todd
author_rank: Regular Contributor
timestamp: January 28, 2019, 08:17:30 am
content: Quote from: Armadillo on January 28, 2019, 07:54:53 amoh really?well then ill just calibrate everthjng else and call it a day, thanks for all your helpSent from my iPad using Tapatalk