Took the Plunge - GoldStar OS-7020 Oscilloscope - Page 1
Forum section: electronics / beginners

author: olafwagner
author_rank: Contributor
timestamp: January 05, 2020, 04:08:27 pm
content: Hi All,I have been a longtime 'watcher' of EEVBlog, but am new to the forum. I have been an electronics enthusiast for a long time, but decided to 'level-up' to a scope. I took Dave's advice (from one of the videos) to be willing to cut my teeth on an analog scope, so when I stumbled onto a dirty GoldStar OS-7020 2-channel 20Mhz scope, I went for it (even though it didn't come with any probes, power cords or documentation at all). I attached a picture below.I have cleaned it up, and the scope looks much better and it is working, but it does need urgent calibration. When I switch it to XY mode I don't get a 'dot' but rather a 'dash' on the screen that I can move around.At this point I am trying to track down a service manual - because I don't want even think about 'experimenting' by turning trimmers without knowing which does what.Anyway, happy to have joined this community.

author: james_s
author_rank: Super Contributor
timestamp: January 05, 2020, 05:24:15 pm
content: That isn't a calibration issue. Either you're picking up noise on the X input or the astigmatism of the beam is way off. I don't see an astigmatism control on the front panel so I'd first look at the noise possibility. Is the V/div set the same on both channels? What happens if you short out the X input?

author: olafwagner
author_rank: Contributor
timestamp: January 05, 2020, 06:05:54 pm
content: Yes, the v/div is set the same on both channels, and have even shorting x-input has absolutely no effect. So I am hoping it is simply astigmatism, but I don't have the service manual yet, so I don't know where to 'fiddle'.That being said, I just found the service manual for the GoldStar OS-9020, and while they are somewhat different scopes, that manual might show me the 'region' of the astigmatism control, and then I'll try to find the same on the 7020's schematics.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 05, 2020, 06:18:24 pm
content: To see if it's because of the spot's astigmatism, connect the calibrating signal to one channel (with a simple wire if you don't have probes) and look at the raising and falling edges of the signal. The trace on the raising/falling sections should be even thinner than the horizontal regions of the trace.The astigmatism can be seen even better with a sinusoidal signal, but the square calibrating signal would do it, too.

author: olafwagner
author_rank: Contributor
timestamp: January 05, 2020, 06:45:32 pm
content: The calibrating signal highlights a number of issues:- There are no visible vertical lines just horizontal ones- The lines overlap a bit (I assume this also points to an astig. issue)- Calibration: This signal is .5v and my scope is set to .1v/div so there should only be 5 divisions yet it shows 6 (similar calibration issue on the time axis, it is slightly out)- There is a visible 'retrace' at the bottom (is that what it is called when the beam returns to the left?)- The image is a bit 'bowed'- There is a slight 'overshoot' on the voltage (I assume this is somewhat normal with analog scopes)For reference, I also hooked up the Goldstar's test signal to my cheap digital scope (please excuse the dust) where I can see that the calibration signal being generated is pretty clean.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 05, 2020, 06:53:24 pm
content: That's astigmatism, no doubt, and a very strong one. That is why the vertical sections are not visible at all, and also the cause upper and lower horizontal sections are overlapping on the horizontal direction.

author: nfmax
author_rank: Super Contributor
timestamp: January 05, 2020, 06:59:30 pm
content: It looks like you have the intensity set too high - if you turn it down, the retrace should disappear. That may also improve the astigmatism. Is there an astigmatism adjustment on the back panel, or through a hole in the side cover? It was often just a screwdriver operated control.Edit to add: if the calibration is off in both axes, and the retrace blanking isn't working properly, and there is astigmatism, that all points to an HT/EHT fault somewhere. However, the focus looks OK, and the trace is bright, which makes it unlikely to be EHT.

author: rstofer
author_rank: Super Contributor
timestamp: January 05, 2020, 07:43:34 pm
content: Not only is your trace "blooming" with excessive brightness, a 20 MHz scope won't be capable of displaying the rising edge of any decent square wave source. You might change the time per division such that you only display the area close to the rising edge. That may help see it but I kind of doubt it.None of this matters. Sure, a 100 MHz DSO is a higher end tool (and it is considered 'entry level') but I got along for a very long time with a Heathkit 10 MHz scope. Given the emphasis on Arduino projects, 20 MHz will be fine.Enjoy!

author: james_s
author_rank: Super Contributor
timestamp: January 06, 2020, 01:56:38 am
content: Even a 5MHz scope will display what looks like a reasonable rising edge of a square wave, you just won't be able to accurately measure the rise time. I had a 5MHz Heath scope when I was a kid and it would show a nice clean looking square wave of at least a few tens of kHz. Looking at a square wave on an analog scope of any sort you will mostly see the flats on the top and bottom, the rising and falling edges will be faint but visible when the scope is operating correctly. I think whatever is causing the severely out of round spot in this case is most if not all of the issue.

author: olafwagner
author_rank: Contributor
timestamp: January 10, 2020, 11:08:11 pm
content: I scoured the boards and found the ASTIG trimmer on the Power Supply Board, and the INTEN ADJ on the Horizontal Board in the 'CRT Drive' section (they have divided the board into logical groups with handy silkscreening) (see pics below)After fiddling with both of these trimmers (as well as the 'Focus' and 'Inten' controls on the front, I am still facing a few problems:- I still cannot get the XY down to a 'dot', it remains a 'dash'.- The 'Inten' control on the front panel isn't doing anything (it doesn't noticeably make the trace brighter or dimmer. Similarly, turning the INTEN ADJ trimmer on the board also doesn't seem to change anything.I wonder whether these problems are related?As an aside they also handily silkscreened some of the output voltages for the power supply, so I tested the 5v, 12v, -12v, 50v, 160v and 180v rails and they all seem to be very close. (I haven't measured the HV because I don't have a HV DMM Probe yet)

author: james_s
author_rank: Super Contributor
timestamp: January 11, 2020, 01:06:53 am
content: I bet they are. The fact that the intensity pot doesn't do anything clearly indicates that something is wrong. Can you find a schematic for the scope? Even a the schematic for a vaguely similar scope might be enough to give you an idea. At the very least you should be able to find a pinout for the CRT and you can look at the intensity and blanking circuits. Look around for open resistors or a shorted transistor. At the very least figure out the intensity problem before you bother troubleshooting anything else.

author: olafwagner
author_rank: Contributor
timestamp: January 11, 2020, 03:51:51 am
content: I am still working on tracking down a schematic for this EXACT model. The closest I have is the GoldStar OS-7020A, which seems to be very very similar, but all the component numbers are slightly different than what I see on my PCB's.I attached a schematic (below) for the H.V. CRT Drive, where I have tracked down the 'INT ADJ' trimmer in the model, and the connector to the INTEN pot towards the left.Unfortunately I am not skilled enough to know where the Intensity and Blanking circuits are (or what they even do), therefore the only way I would go about this would be to work my way backwards from the pot and trimmer and check each resistor along the way.

author: olafwagner
author_rank: Contributor
timestamp: January 11, 2020, 04:57:54 pm
content: I have a few questions for those who are able to read schematics like 'sheet music' :-)(With reference to the attached schematic with highlights)- In order to handle this PCB safely, I assume I only need to ensure that I discharge C691, C692 and C697 (They are all circled in red, and they are high voltage caps and looks like 1000F each)- I assume all the 0.01u caps (circled in yellow) are of no concern due to low capacitance values- I understand the +12V and -12V rails on the schematic, but in your experience, what does +12DEC and -12DEC mean? I see there is a small schematic (lower left, circled in pink) which looks like +12DEC is simply +12v passed through a 10 ohm resistor and a 22u cap to ground. Does 'DEC' mean 'decreased' or maybe 'decoupled'? What does that mean and what is typically the purpose?- How does Q612 (circled in orange) work in this configuration? The base is permanently grounded so I guess this transistor never switches on and off? Is it always on?- I am trying to decipher what the upper portion of the schematic (circled in light-blue dotted) is supposed to do, but frankly I have no idea. I assume this has something to do with blanking, because there is a connection to the 'Ext Blanking Input' (connector on the rear of the scope) to the left, and eventually connects to P615 Pin 5, which is labeled as the 'Blanking' pin to the CRTThis is going to be a fun journey. I wish I knew more, but as long as I learn something every day, eventually I will get my head around this.

author: james_s
author_rank: Super Contributor
timestamp: January 12, 2020, 12:22:57 am
content: I haven't seen that 'DEC' nomenclature before but looking at the circuit I think your guess of "decoupled" is absolutely right. The resistor and capacitor form a low pass filter and prevent transients on one side from affecting the other, it's a bit like the spring and shock absorber on your car. As long as you have the specified voltages present I wouldn't worry about that right now. I would start at the two intensity pots, first check the voltage on each of the two outer pins relative to ground and verify that it's reasonably close to what's shown in the schematic, if it's not then we can start looking to see if the circuit you have is different or if there's actually a fault there. Then check the voltage at the center pin of each of those pots, it should vary between the levels on the side pins. Not sure what that transistor with the base grounded is doing, I'll have to think about that, maybe one of the analog experts here will know.

author: AVGresponding
author_rank: Super Contributor
timestamp: January 12, 2020, 11:11:51 am
content: Q612?Its emitter is biased to -12v, so the base is effectively +12v with respect to the emitter...

author: Brumby
author_rank: Unknown
timestamp: January 12, 2020, 12:22:52 pm
content: I picked up this exact model late last year - with the service manual - and Olaf has already PM'd me about getting a scan of it. I've been busy lately, but I should have a chance over the next 2 days to get that done.It has several schematics.

author: Brumby
author_rank: Unknown
timestamp: January 16, 2020, 10:58:28 am
content: Hope this will help you out. (I don't think I missed anything)https://www.dropbox.com/s/rybj78uwiksgupo/Goldstar_OS-7020_Service_Manual.pdf?dl=0File size is around 19MB - but I feel this is on the high side. If anyone can recommend some PDF wrangling software that might deliver a smaller file size, I'd be interested.I've presented it as it was in the hardcopy, so viewing on screen should be fine, but printing it out as is might not give you what you expect.

author: olafwagner
author_rank: Contributor
timestamp: January 16, 2020, 03:57:53 pm
content: Thank you very much, this is absolutely brilliant.I am going to immerse myself and try to figure things out. This will make for some excellent 'bedtime reading' tonight :-)

author: Brumby
author_rank: Unknown
timestamp: January 17, 2020, 01:13:41 am
content: Glad you like it. I did try for a decent result - but that's just me.Enjoy.

author: rsjsouza
author_rank: Super Contributor
timestamp: January 17, 2020, 01:32:49 am
content: Brumby, can you try to upload to K04bb site? I have downloaded very high resolution scans there (600dpi grayscale for schematics) and the site is a very precious aggregator of manuals.P.S. I am on my cellphone, otherwise I would do it.

author: Whales
author_rank: Super Contributor
timestamp: January 17, 2020, 01:43:25 am
content: Holy crapola thankyou Brumby. I have the 7040A model (40MHz) and I was coming here to say I've never had any luck finding schems.olafwagner: DC drifts on mine slowly as it warms up, but apart from that it's in perfect working order. Shoot me if you want photos or measurements of any parts.EDIT:previous topic RE my scope

author: Brumby
author_rank: Unknown
timestamp: January 17, 2020, 03:13:15 am
content: Quote from: rsjsouza on January 17, 2020, 01:32:49 amDone.I changed the file name to:Goldstar_OS7020_Oscilloscope_Service_Manual.pdf... to follow the preferred convention for that site.

author: olafwagner
author_rank: Contributor
timestamp: January 21, 2020, 03:17:55 am
content: OK, I have started digging into this further now that I have the service manual (many thanks again Brumby, it is perfect).1. Power SupplyI checked all the low voltage rails, and they are all within spec. Now that I received my HV probe, I checked the HV rail and it seems to be a bit low (or is that high?). According to the service manual, it is supposed to fall between -1,995v to -1,805v but I am measuring -1,650v. I hope I am doing this correctly, is this a DC voltage (service manual doesn't say), and I connected the HV Probe ground terminal to chassis ground. Is this too far out of spec?2. Working Backwards from Intensity PotAfter looking at the 'HV CRT Drive' schematic, I started at P604 Pin 4 and measured voltages. Turning the pot sweeps from -6.6mV (~0v) through to -11.76V (effectively -12v rail) so I believe the pot works correctly.While I was scouring the internet for this service manual (prior to getting it from Brumby) I discovered that the Hitachi V-212 is a very similar scope with pretty similar schematic layout. In their service manual, they handily include some interesting scope diagrams for various points on the board and there I saw that they included a diagram for the spot between the 2 nearest transistors to the intensity pot. (I attached it below and highlight the scope diagram in question)I immediately hooked up my 'cheapo-scope' to my board, and made an interesting discovery. When I connect 'downstream' of transistor Q621 at a point I labeled "P1" in the attached image, then I get a similar signal (is this the blanking signal?)However, if I connect the scope to "P2" (between the 2 transistors, similar to the Hitachi scope), then I just get a constant flat 1.34vDoes that seem right?

author: olafwagner
author_rank: Contributor
timestamp: January 21, 2020, 03:19:10 am
content: Doesn't seem the last 3 images made it, here they are...

author: AVGresponding
author_rank: Super Contributor
timestamp: January 21, 2020, 06:11:34 am
content: Looks like q621 might be toast, that constant 1.34VDC is about what I'd expect to see from the bias resistors of q622, there should be a blanking signal at p2 as well as p1

author: Brumby
author_rank: Unknown
timestamp: January 21, 2020, 06:13:27 am
content: Quote from: olafwagner on January 21, 2020, 03:17:55 amYou can safely assumeanyvoltages specified in circuit diagrams will be DC - unless they are very clearly annotated otherwise. Power supply voltages tend to be the safest bet as being DC.

author: james_s
author_rank: Super Contributor
timestamp: January 21, 2020, 06:40:21 am
content: If it gives you a range of -1,995v to -1,805v and you're seeing only -1,650V that's way low, I'm not sure offhand why it's low but that definitely isn't right.

author: olafwagner
author_rank: Contributor
timestamp: January 22, 2020, 08:49:20 pm
content: I removed Q621 from the board and popped it into my component tester, and it recognized it as being a BJT-NPN transistor (see attached).Unfortunately I don't know what the hFE, Ube and Ic values mean, but considering the tester recognized this as a NPN transistor, does it still mean that Q621 is bad?I googled for a data sheet, and found one for a Hitachi 2SC1907, and also attached some of the electrical characteristics below (unfortunately I don't know what to look into)

author: james_s
author_rank: Super Contributor
timestamp: January 22, 2020, 10:33:43 pm
content: Those characteristics are useful if you are designing something around a transistor or trying to find a suitable sub but that isn't important right now. You are correct in assuming that if the tester accurately identifies it as an NPN transistor it is almost certainly just fine. 99% of the time a fault will clearly manifest itself as a short or open between two or more pins.

author: AVGresponding
author_rank: Super Contributor
timestamp: January 23, 2020, 01:48:46 pm
content: Agreed, normally the failure mode is a fairly clear open or short.Does seem strange that the blanking signal ends there though...

author: olafwagner
author_rank: Contributor
timestamp: January 23, 2020, 09:48:52 pm
content: I have been prodding around the board some more measuring voltages, but I must admit I am at a bit of a loss.Here is a list of Summarized List of Signs and Symptoms:- After switching on, it takes 30-35 seconds for the trace to appear (I would expect 10-15 to be more typical, this seems long)- HV Rail measures -1,650v. (Should be in the range of -1,995v to -1,805v.)- Intensity Pot (and internal trimmer) cannot get the trace to disappear. (It seems to alter the brightness ever so slightly, but not even close to disappearing.)- Blanking Signal not getting to the Blanking Amp- Trace is a 'dash' and not a 'dot' (very obvious in low-speed sweeps or XY mode)I tried to make some progress on any of these issues by doing the following:1. Blanking Signal- I measured a lot of voltages around the blanking amp trying to figure out why the blanking signal never gets 'through' Q621. (all measured voltages appear in red in the attachment below)- I also pulled Q622 off the board and popped it into my component tester, and it is also recognized correctly.- I noticed in the Hitachi spec that they also have an oscilloscope diagram for what I assume is the output of the blanking amp (before it hits high-voltage), which I am calling "P3". When I attached my scope there I only get a flat signal which I have measured to be 13.5V- I also tried to measure diode CR621 (1SS83) in circuit with my DMM in continuity mode, but I do NOT get a 'beep' in either direction. Should I get a beep? Or must these be removed from the board and plugged into a component tester to test?- Lastly I ordered a couple of replacement 2SC1907's from Ebay, so I could simply replace Q621 and Q622 and see whether that does anything.2. Intensity ControlsI previously measured all the voltages around the INTEN pot (and included the measured voltages on the schematic)- Today I measured all the voltages around the internal INTEN ADJ. trimmer. I assume they appear correct. I stopped short of diode CR516, because that is inside the high voltage area of the board that has a nice protective shield over it.3. HV RailHere I am seriously out my depth (and do not want to electrocute myself) so I can only do very little testing.- I measured a few voltages on the input side that goes to the HV transformer (just to make sure the 18v rail was getting here properly)The 'simplest' issue that I need to progress on is the blanking signal, so my only hope there at the moment is simply replacing Q621 and Q622 and see what happens.

author: james_s
author_rank: Super Contributor
timestamp: January 23, 2020, 10:32:23 pm
content: If those are HV diodes then the forward drop will be too high to measure with the diode check on a DMM.Something else that would be worthwhile to test is the CRT itself, check to make sure there are no shorts between elements that should not be connected.

author: olafwagner
author_rank: Contributor
timestamp: January 24, 2020, 02:25:52 am
content: OK, things just got weird.I wigged the CRT socket connector a bit (to make sure it is properly connected, and reinstalled transistor Q622, reinstalled the horizontal board into the case and turned it on.Now all of a sudden I have a VERTICAL problem. The trace is making a vertical line that is the thickest at the center graticule, and if I fiddle with vertical position, only the length of the thin line at the top gets longer and shorter. The fatter part remains in the center of the screen.Also (and more alarmingly), I re-measured my HV rail, and now I get -2,302v!What the heck is going on.

author: james_s
author_rank: Super Contributor
timestamp: January 24, 2020, 03:30:59 am
content: That's odd, sounds like the CRT socket and associated wiring needs a careful inspection.

author: olafwagner
author_rank: Contributor
timestamp: January 31, 2020, 08:51:17 pm
content: I carefully unplugged and removed the CRT, and checked all of the pin combinations. The only combination that I got a 'continuity beep' on were pins 1 & 14, which I believe is the heater, so I assume that is correct. Also, with nothing visibly wrong with the CRT and nothing rattling around inside, I carefully installed it again.I checked the CRT socket board and all the pins and harness, but I cannot find anything wrong here. (All continuity beeps out, nothing seems shorted)I then turned my attention to the HV circuit (because something there must be causing this spike to -2,302v. I opened up the cover to the HV section, and checked all the resistors (they all check out fine within spec), but noticed resistor R697 was missing. I then removed the PCB and looked underneath.Firstly I discovered that I am certainly not the first here. There is some liquid residue on the board, which I assume is flux that someone before me didn't clean off. It also looks like a lot of the solder points may have been remelted (perhaps whoever had this scope before me assumed there were dry solder joints.Secondly I found resistor R697 installed underneath (perhaps by the same person that left the other evidence). However, even though the schematic calls for a 3M resistor, there is a 1M resistor installed. This resistor is part of the FOCUS circuit, and the resistor on the other side is a 16M, so assume the 1 vs 3M won't make a huge difference, and is probably not related to my sudden high voltage issue.Should I remove and test all the 2KV and 3KV ceramic capacitors and test them? (I assume Ceramic caps are very reliable?) Should I remove and test the diodes? (I assume these are far too high voltage to be able to 'beep' in circuit)Also, what role do the 2 Neon Lamps (NL601 and NL602, type NE-68 which is either an old or unobtainium model) play? I see they are wired across the Blanking and Cathode rails (in series with one another), is this some kind of voltage regulation? How would I go about checking them? Should I see them 'glow'? (because I don't)

author: james_s
author_rank: Super Contributor
timestamp: February 01, 2020, 12:40:09 am
content: Ah so it sounds like you're dealing with someone elses failed repair, you're going to have to look very carefully because there's no telling what else they messed with in there. I would change out that 1M resistor for the proper 3M or three 1M resistors in series, that could be increasing the load significantly on the HV which is not able to supply much current. Also clean off the flux, some types of flux are conductive and that also can cause problems with high voltage and high impedance circuits.The neon lamps are likely functioning as spark gaps, their purpose is to protect the electronics in case an arc occurs in the CRT. It's fairly common to see that arrangement on older CRT displays.

author: Brumby
author_rank: Unknown
timestamp: February 02, 2020, 10:59:21 am
content: Quote from: Brumby on January 16, 2020, 10:58:28 amPDF has been updated. It is now searchable and just under 11MB in size. The new version has just been uploaded to KO4BB and Dropbox.Dropbox link is:https://www.dropbox.com/s/m8robnt2kxczc9g/Goldstar_OS7020_Oscilloscope_Service_Manual_searchable.pdf?dl=0In a moment of weakness I spent some real money on PDF software.

author: AVGresponding
author_rank: Super Contributor
timestamp: February 02, 2020, 04:20:15 pm
content: Quote from: Brumby on February 02, 2020, 10:59:21 amPlease excuse me if I'm missing something obvious here, but couldn't you just use a compression tool on the file?

author: Whales
author_rank: Super Contributor
timestamp: February 03, 2020, 04:23:36 am
content: Quote from: ThickPhilM on February 02, 2020, 04:20:15 pmCompression backgroundTo be able to answer both of these questions: some background about compression is needed.There are lossless compression techniques (eg .zip, .rar, .gz, .lzma, .7z, png) and lossy compression techniques (jpeg, most video codecs [h264, mpeg*], most audio codecs [opus, mp3, aac]). Lossy is a lot better at saving space, but it sacrifices some details.Lossy is pretty much a default expectation of modern computing and society, with lossless only used where any loss would be inappropriate (eg text files, written documents).Lossy compressors are very situation specific so I won't go into their details here. Most have variable control: more compression (more detail loss) or less compression (less detail loss). You may have encountered this when saving as JPEG.Lossless compressors work by looking for repeating patterns in your files and replacing these repeating patterns with just one copy (plus some references). This is how archive formats like .zip, .rar and .7z work.Regardless of what compression technique you use: the data bits and bytes in the output compressed file should look mostly indistinguishable from random data. This means that there are no obvious patterns left that can be exploited for further compression. ie compressing a file multiple times will not make it smaller (with some technical exceptions), only one layer of compression should be applied or needed (again with some weird exceptions, not relevant here).Initial inspectionNow let's look at the specific PDF file: Goldstar_OS-7020_Service_Manual.pdf (19MiB). I'll start my inspecting by extracting all of the images usingpdfimages(part of poppler-utils):Code:$ pdfimages ../GoldStar.pdf -all ex$ lsex-000.jp2 ex-039.jpg ex-078.jpg ex-117.jpg ex-156.jpg ex-195.jpg ex-234.jpg ex-273.jpgex-001.jpg ex-040.jpg ex-079.jpg ex-118.png ex-157.jpg ex-196.jpg ex-235.jpg ex-274.jpgex-002.jpg ex-041.jpg ex-080.jpg ex-119.jpg ex-158.jpg ex-197.jpg ex-236.jpg ex-275.jpgex-003.jpg ex-042.jpg ex-081.jpg ex-120.jpg ex-159.jpg ex-198.jpg ex-237.jpg ex-276.jpgex-004.jpg ex-043.jpg ex-082.jpg ex-121.jpg ex-160.jpg ex-199.jpg ex-238.jpg ex-277.jpgex-005.jpg ex-044.jpg ex-083.jpg ex-122.jpg ex-161.jpg ex-200.jpg ex-239.jpg ex-278.jpgex-006.jpg ex-045.jpg ex-084.jpg ex-123.jpg ex-162.jpg ex-201.jpg ex-240.jpg ex-279.jpgex-007.jpg ex-046.jpg ex-085.jpg ex-124.png ex-163.jpg ex-202.jpg ex-241.jpg ex-280.jpgex-008.jpg ex-047.jpg ex-086.jpg ex-125.jpg ex-164.png ex-203.jpg ex-242.jpg ex-281.jpgex-009.jpg ex-048.jpg ex-087.jpg ex-126.jpg ex-165.jpg ex-204.jpg ex-243.jpg ex-282.jpgex-010.jpg ex-049.jpg ex-088.jpg ex-127.jpg ex-166.jpg ex-205.jpg ex-244.jpg ex-283.jpgex-011.jpg ex-050.jpg ex-089.jpg ex-128.jpg ex-167.jpg ex-206.jpg ex-245.jpg ex-284.jpgex-012.jpg ex-051.jpg ex-090.jpg ex-129.jpg ex-168.jpg ex-207.jpg ex-246.jpg ex-285.jpgex-013.jpg ex-052.jpg ex-091.jpg ex-130.jpg ex-169.jpg ex-208.jpg ex-247.jpg ex-286.jpgex-014.jpg ex-053.jpg ex-092.jpg ex-131.jpg ex-170.jpg ex-209.jpg ex-248.jpg ex-287.jpgex-015.jpg ex-054.jpg ex-093.jpg ex-132.jpg ex-171.jpg ex-210.jpg ex-249.jpg ex-288.jpgex-016.jpg ex-055.jpg ex-094.png ex-133.jpg ex-172.jpg ex-211.jpg ex-250.jpg ex-289.jpgex-017.jpg ex-056.jpg ex-095.jpg ex-134.jpg ex-173.jpg ex-212.jpg ex-251.jpg ex-290.jpgex-018.jpg ex-057.jpg ex-096.jpg ex-135.jpg ex-174.jpg ex-213.jpg ex-252.jpg ex-291.jpgex-019.jpg ex-058.jpg ex-097.jpg ex-136.jpg ex-175.jpg ex-214.jpg ex-253.jpg ex-292.jpgex-020.jpg ex-059.jpg ex-098.jpg ex-137.jpg ex-176.jpg ex-215.jpg ex-254.jpg ex-293.jpgex-021.jpg ex-060.jpg ex-099.jpg ex-138.jpg ex-177.jpg ex-216.jpg ex-255.jpg ex-294.jpgex-022.jpg ex-061.jpg ex-100.jpg ex-139.png ex-178.jpg ex-217.jpg ex-256.jpg ex-295.jpgex-023.jpg ex-062.jpg ex-101.jpg ex-140.jpg ex-179.jpg ex-218.jpg ex-257.jpg ex-296.jpgex-024.jpg ex-063.jpg ex-102.jpg ex-141.jpg ex-180.jpg ex-219.jpg ex-258.jpg ex-297.jpgex-025.jpg ex-064.jpg ex-103.jpg ex-142.jpg ex-181.jpg ex-220.jpg ex-259.jpg ex-298.jpgex-026.jpg ex-065.jpg ex-104.jpg ex-143.jpg ex-182.jpg ex-221.jpg ex-260.jpg ex-299.jpgex-027.jpg ex-066.jpg ex-105.jpg ex-144.jpg ex-183.jpg ex-222.jpg ex-261.jpg ex-300.jpgex-028.jpg ex-067.jpg ex-106.jpg ex-145.jpg ex-184.jpg ex-223.jpg ex-262.jpg ex-301.jpgex-029.jpg ex-068.jpg ex-107.jpg ex-146.jpg ex-185.jpg ex-224.jpg ex-263.jpg ex-302.jpgex-030.jpg ex-069.jpg ex-108.jpg ex-147.jpg ex-186.jpg ex-225.jpg ex-264.jpg ex-303.jpgex-031.jpg ex-070.jpg ex-109.png ex-148.jpg ex-187.jpg ex-226.jpg ex-265.jpg ex-304.jpgex-032.jpg ex-071.jpg ex-110.jpg ex-149.jpg ex-188.jpg ex-227.jpg ex-266.jpg ex-305.jpgex-033.jpg ex-072.jpg ex-111.jpg ex-150.jpg ex-189.jpg ex-228.jpg ex-267.jpg ex-306.jp2ex-034.jpg ex-073.jpg ex-112.jpg ex-151.jpg ex-190.jpg ex-229.jpg ex-268.jpg ex-307.jp2ex-035.jpg ex-074.jpg ex-113.jpg ex-152.png ex-191.jpg ex-230.jpg ex-269.jpg ex-308.jp2ex-036.jpg ex-075.jpg ex-114.jpg ex-153.jpg ex-192.jpg ex-231.jpg ex-270.jpgex-037.jpg ex-076.jpg ex-115.jpg ex-154.jpg ex-193.jpg ex-232.jpg ex-271.jpgex-038.jpg ex-077.jpg ex-116.jpg ex-155.jpg ex-194.jpg ex-233.jpg ex-272.jpgIt looks like this file is nothing but jpegs and the occasionaljp2. That means to further (re)compress this file: what we really need to do is focus on the jpegs. The PDF is nothing but a wrapper around them. This is basically always the case for scanned PDFs.We have several options to reduce the file sizes of images:Reduce their size (resolution)Reduce their bitdepth (number of colours)Increase their compression level (throw out more data during lossy/jpeg compression)Change the lossy codec to something else (eg from jpeg to jp2)Sidenote: file quirks & better softwareUnfortunately for us each page of this PDF is not a single jpeg. Each page has been split into multiple jpegs that are aligned together in a grid:Some software does this, it's quite annoyingTo work around this: we're going to use theimagemagicktools from now on. These are smart enough to treat each page as a single image. This particular software is very common and well known in the *nix and web-development worlds (many websites use it behind the scenes for image processing), but not well known in the Windows world, even though there is a Windows version available. The world is weird, this software is theduck's gutsfor anything that requires mass-editing of multiple files simultaneously.My method(1) Remove the very first and last pages. It's pretty to see the paper texture from the original manual cover, but it's all undulating and hard to compress. The second page of the PDF is the same as the cover any, just in black and white.(2) Convert everything to greyscale. There is no point having colour anywhere in this document, so let's not make the compressor (eg jpeg) think it has to preserve it. Strip it all out.(3) Remove ghosted text from other pages by fiddling with brightness/levels. I'm talking about this stuff (emphasized via editing):You can't (normally) see this and it's useless, so let's get rid of it. The fact it's still there in the image means the last person's compressor was wasting space trying to keep it.(4) Avoid reducing the resolution. Resolution is nice, esp in technical documents. There's nothing worse than a blurry technical diagram. The whole point of these documents is to make people happy, not grumpy.(5) Try several different compressors (jpeg, jpeg2000, png, etc). PDFs can house quite a few different formats fine.First attempt: adjust levels, greyscale, jpegCode:$ mkdir temp1$ magick convert -density 100 Goldstar_OS-7020_Service_Manual.pdf -set colorspace Gray -level '25%,75%,0.3' -quality 70 'temp1/page%03d.jpeg'$ rm temp1/page000.jpeg temp1/page099.jpeg$ du -sh temp1/9.1M9.1MiB is not bad, but we can be squeezier if we're clever.Second attempt: adjust levels, greyscale, pngCode:$ convert -density 100 Goldstar_OS-7020_Service_Manual.pdf -set colorspace Gray -level '25%,75%,0.4' 'temp2/page%03d.png'$ rm temp2/page000.png temp2/page099.png$ du -sh temp2/12MEep, wrong way. This codec doesn't seem useful with this sort of image data.... but what if we massage the image into something that png would actually like? Eg black and white (no greyscale)?Third attempt: threshold into black and white, pngCode:$ convert -density 100 Goldstar_OS-7020_Service_Manual.pdf -set colorspace Gray -alpha off -auto-threshold OTSU 'temp3/page%03d.png'$ rm temp3/page000.png temp3/page099.png$ du -sh temp3/1.7MI think the resolution is a bit low however, so I up it to-density 200and try again:Code:$ du -sh temp43.8MNot as good filesize wise, but the diagrams are a lot more readable.

author: Whales
author_rank: Super Contributor
timestamp: February 03, 2020, 04:26:31 am
content: Turning the individual image pages back into a single PDFI think it's possible to use imagemagick to do this, but you have to tell it not to recompress the files a second time. Instead I usedimg2pdf(probably not easy to get on Windows):Code:$ img2pdf temp3/* -o Goldstar_OS7020_servicemanual_tiny.pdf$ img2pdf temp4/* -o Goldstar_OS7020_servicemanual_reasonable.pdfThe results are attached.I have not spent enough time quality checking: some of the large diagrams have unreadable numbers. It's also hard to differentiate grid lines and signal on the scope shots; perhaps thresholding in black-and-white wasn't the best option here.OpinionDon't throw out the original scans. Keep both the original scans PDF and a small PDF (like mine) side by side and never separate them. One for convenience, the other for when the convenient version screws up (unreadable detail). You can't recover data that has been thrown out.Text searchabilityAlso known as OCR (optical character recognition). Never 100% accurate but useful. Not going into it heresounds like you already have something that works.I want a program that can do all of this for me!No such program will ever exist, just as there will never be a program that writes the manual for you. Every step of the above has required human analysis and choosing between one of many options.There will be programs that will claim to compress PDFs, but their performance will be hit and miss because they will guess at what is best to do. None of these programs try to read the circuit diagrams afterwards and determine if they are readable or not. None of these programs can tell that ghosted text from other pages is not useful information. And so on.We are after all trying to compress against human perception, not machine perception.

author: Brumby
author_rank: Unknown
timestamp: February 03, 2020, 06:18:55 am
content: It's amazing how you can ask for suggestions and get ignored - but put something out there that isn't up to some people's expectations and watch all the experts chime in.Yes, I know there was colour. Yes, I know there was some text visible through the back of the page. Yes, I could have reduced it to greyscale - but my efforts took long enough as it was, scanning each page separately, keeping things as square as possible and as clear as possible, stitching together pages that had to be done in two passes because they were too big for the scanner.Considering that this was my first foray into PDF wrangling, the result seems useful enough. I've already admitted it isn't optimal.Here's the original scan that came straight off the scanner...https://www.dropbox.com/sh/dqj8qe9jvfodvfz/AACdycgDv4HgFte3aI7KPHLra?dl=0&preview=Goldstar_OS7020_ServMan_OriginalScan.PDF(There are a couple of pages that were double scanned.)Knock yourself out.Edit: Bit of a rant there.... sorry.

author: AVGresponding
author_rank: Super Contributor
timestamp: February 03, 2020, 10:28:34 am
content: Haha no worries.I know the basics regarding lossy and lossless compression; I recently completed an HNC with the OU that included these topics.I just wasn't aware of the quality of the source material you were working with, that's quite an effort you put in there!

author: rsjsouza
author_rank: Super Contributor
timestamp: February 03, 2020, 11:43:19 am
content: Whales, your posts above are pretty well written indeed, thanks for taking the time.One question I have: does the process of removing the background shade performs yet another decompression/recompression? I suspect not, but wanted to ask.As for the utilities, I usually use IrfanView and Foxit for this handling. They tend to do quite a reasonable job, but I will check these tools as well.In my opinion, however, Brumby's grayscale version looks much more appealing to my eyes than your two versions above.When I got my Keithley 191, its online manual at Tektronix was scanned in BW with very poor detailing overall, with blocky graphics (due to the threshold in BW conversion) and other issues. I got a physical copy, scanned it in uncompressed 300dpi TIFF (schematics and mechanicals at 600dpi) and worked around to compress it to a more reasonable size. Sure, the file size is much larger than theirs (26MB) but disk space is cheap, internet connections are improving and there are no continuous upgrades, thus making it a one time process.One thing I may do to this and another manual I posted there is the removal of the shading of the other pages - a brightness setting on the scanner would have minimized/solved this.

author: Brumby
author_rank: Unknown
timestamp: February 03, 2020, 12:33:04 pm
content: Quote from: rsjsouza on February 03, 2020, 11:43:19 amThis is why I avoid threshhold processing for text. The intermediate intensity pixels add clarity when viewed by our eyes, which - in conjunction with the human brain - have developed algorithms to see things much more clearly.Reducing the ghosting from the back of the pages would have been useful - so would converting from a colour palette to greyscale.

author: rsjsouza
author_rank: Super Contributor
timestamp: February 03, 2020, 03:06:32 pm
content: Quote from: Brumby on February 03, 2020, 12:33:04 pmYes, that is the effect also brought by some of these subpixel rasterizing methods. Interesting that Microsoft's ClearType uses RGB, not only greyscale, but I imagine that greyscale is already good enough for these manuals.

author: Whales
author_rank: Super Contributor
timestamp: February 04, 2020, 09:33:05 pm
content: Quote from: rsjsouza on February 03, 2020, 11:43:19 amYes it does.Original jpegs -> decompress into raw (in-memory) pixels -> adjust levels to remove background ghosts -> compress into new jpegThere are tools that can edit JPEGs directly (ie without decompression), but they're pretty rare and would be limited. It should be theoretically possible to keep most of the JPEG DCT blocks and throw out just the ones you don't want, ie 'lossless' editing of a lossy format, but I'm not aware of any easy ways.The only mainstream/common lossless JPEG editing available is image rotation, but even then some tools stuff it up and re-compress the image anyway. You only need to edit some metadata for this one.The saving grace is that I destroyed a lot of other detail anyway, so having an extract decompress + recompress really didn't do much harmQuoteI agree as well. I quested for a compression method small enough to attach the PDF on the forums, too much was thrown out.In 2020: a 20MiB PDF is harmless to have on disk, just annoying to transfer over some people's internet connections. Getting it down to the size of a floppy isn't really necessary unless you face arbitrary rules where you want to upload it.QuoteN.B. 'brightness' on different devices means different things. Sometimes it adjusts both the black and white points, others only the white point, in some it even adjusts gamma instead. As a general rule for monitors and scanners: ignore what the controls are named, fiddle with them and work out what they mean yourself.The 'Xsane' scanning utility (Linux) is getting old, but it still works and provides lots of level adjustments & preview options. It was my choice the last time I did some mass scans, but that was a few years back.

author: Whales
author_rank: Super Contributor
timestamp: February 04, 2020, 09:38:24 pm
content: Quote from: Brumby on February 03, 2020, 12:33:04 pmYep.In some situations we can cheat: really high res vector art or vector text can be saved in a thresholded format, then when it gets downscaled onto your screen by your image viewer it looks nice and smooth again. Unfortunately that's not really possible in this situation.QuoteN.B. I had a hard time getting this (levels/curves adjustment) to avoid damaging the greys around the text itself. Text didn't look anywhere as nice, even with some gamma tweaking.There are some smarter tools out there likeunpaper. Not perfect and the output has sections whited out (read:ugly), but pretty good at preserving the text you want.QuoteThis may not save as much data as you expect. JPEG already heavily subsamples the colour out. Not sure of exact %.

author: olafwagner
author_rank: Contributor
timestamp: February 08, 2020, 01:45:20 am
content: I have been quiet for a couple of days waiting for my 3M resistors to arrive.1. Inspecting the PCBWhile waiting for them, I took a closer look at the PCB, and discovered a problem. Firstly I removed the 1M resistor, and when I removed it I saw the pad for the original resistor was missing (probably why it was hacked onto the bottom). Also, I saw that the connector that goes to the 'Focus' pot was loose, and had a broken trace. This immediately gave me a good theory on why the HV rail was first too low, and subsequently too high. My assumption was that focus is connected directly to the HV rail (through the aforementioned R697 in yellow on the attached schematic), and when this resistor was 1M it was 'draining' too much of the HV rail through the focus pot. I believe when I removed the PCB the first time, it may have caused the trace to get damaged (I was so gentle I assume it was already somewhat damaged, but me removing it broke it, and as a result there was no longer ANY current running from the HV rail through R697 and through the Focus pot. Hmmm....2. 3M Resistors (Part 1)Eventually the resistors arrived, and I saw they had '3M' written in pen, but fortunately I double-checked with my DMM and they turned out to be incorrectly labeled. They were actually just 3 Ohm resistors (that would have beeen fun had I installed them). I looked under a magnifier and saw the colors were Orange, Black, Black, Silver, Brown, which backed up the DMM. (3 (Orange) 0 (Black) 0 (Black) * 0.01ohm (Silver) = 3 ohm (with a +-1% tolerance (brown)). I contacted the Ebay seller and to his credit he immediately sent me the proper resistors. Just more time to wait...3. Checking the Caps 'In-circuit'While I waited I thought I would turn my attention to all the relevant capacitors in both the HV and blanking circuits. However, I didn't want to remove each and every one to test them, so I thought I'd do a 'cursory' in-circuit ESR test to see whether anything obvious pops up. The problem is that my ESR meter only offically measures down to 1uF (I have a Signstek MESR-100 v2), and many of these caps are much lower, but regardless I soldiered on and marked those that could be measured (and measured good) in green, and those that came back with no resistance measurement at all in yellow) Unfortunately this didn't highlight any caps as being problematic (I guess that doesn't neccessarily mean that they aren't part of the problem, just not obviously so - or are in-circuit ESR measurements somewhat dependable?)4. 3M Resistors (Part 2)The correct 3M resistors arrived today, so I immediately installed one (as well as a small bodge wire to address the missing pad and broken trace). I also replaced both transistors Q621 and Q622 (might as well while I have the board out), and then reinstalled everything and powered up the scope.At last, I can report a 'baby-step' of progress. The HV rail now reads -1,821v, which now falls WITHIN the spec range of -1,995v to -1,805v (only just, but I'll take it). :-) OK, so my theory above on the wrong resistor value and broken trace turns out to be correct.Unfortunately, all my other issues remain, so there is still some work to do. :-(Two of the issues which I still feel must be related are:- Unblanking signal (which I can see at "P1") does not make it to "P2"- The INTEN Pot (or internal trimmer) are unable to reduce the signal to a blank screen.5. Next StepsSo I have 3 theories (options?):Theory #1: Capacitors: There are only 3 caps in this area (C659, C650 and C649.) (While my schematic shows C671 it is not physically on my PCB nor is there a silkscreen marking for it) I could pull those 3 caps from the board and test them properly out of circuit. I don't feel very strong about this because all 3 tested fine in circuit.Theory #2: Transistors: There are 2 more downstream transistors: Q632 (2SB648A which is a PNP Hitachi Low Frequency High Voltage Amplifier) or Q623 (2SD668A which is the complementary NPN Hitachi Low Frequency Low Voltage Amplifier) Does it make (theoretical) sense that if either of these transistors had a problem it would affect Q622? Doesn't seem logical seeing as the emitter of Q622 goes both to the base of Q623 as well as -12v (through R691), so I would expect Q622 to function regardless of whether its output signal is amplified or not.Theory #3: Diodes: Another very weak theory, but I am unable to test these diodes in-circuit with my DMM, I just don't get a 'beep' in either direction on ANY of the diodes (my DMM just doesn't crank out enough volts I guess). Is there a safe way to test these diodes in circuit? Or should I pull them and plug them into my component tester? (there are about 4 or 5 in the vicinity).Those are pretty much all the options I can think of. The only other components are resistors, and I have measured all of them in-circuit and they all read very very close to their expected values.

author: olafwagner
author_rank: Contributor
timestamp: February 08, 2020, 04:49:50 am
content: I was poking around the board some more taking measurements, and I got 'something' at "P2" by turning the intensity ALL the way up, but what I see doesn't make sense.I left the scope running, had some dinner and when I came back I switched it off, and heard a lot of static 'pops'. I switched it on again, and while measuring some more, I heard more pops that sounded like they were coming from near or around the CRT. As I switched off the scope and was staring at the CRT I saw a few tiny sparks (accompanied by pops) on the power supply board (on the negative pin of one of the big caps) I immediately discharged all the caps again and removed the power supply board.When I inspected the board, I saw yet another damaged trace at capacitor C821, which sits between the 160v and 180v rails. I measured the ESR on the cap (and it measured good), so at first I just wanted to fashion another bodge wire, but I thought I am so close, I am going to remove this cap and test it properly.I heated up the soldering iron, and as soon as I touched the negative pin (where the broken trace is), I heard the classic 'simmering' sound, and I knew, this cap has leaked. I then removed the cap entirely, and it is nice and wet on its underside (see attached pics).Also when I removed it, (of course), the pad immediately broke loose. The broken trace also means that the 160v rail will not work (because that pad sits inline), so while I didn't retest my 160v rail recently, I assume that it couldn't have worked (or at least not properly)For giggles I hooked it up to my LCR and it still measured 763uF (should be a 1000uF cap) which is more than I was expecting, but certainly far out of 'spec'.Now I need to order a replacement (I don't have anything close to this large in my stash). I am curious that this is only a 50v cap, when it sits between the 180v and 160v rails. (even the schematic calls for a 1000uF 50v cap) Is this because the delta is just 20v? Or should I try to find a cap with a higher voltage rating?

author: AVGresponding
author_rank: Super Contributor
timestamp: February 08, 2020, 09:30:48 am
content: The cap rating of 50V is because in normal operation it doesn't see more than 20V (though if one of the rails it's connected to fails to 0V, it's not gonna be happy!), and a 1000uF cap with a say, 200V rating would bebigand expensive.Since its bum is still wet, I'd guess it's a recent failure.One problem with testing caps for leakage failure is that it often doesn't manifest until you get close to operating voltage, or at any rate, well above the voltage that most LCR meters put out.EDIT: Also,on those 3M resistors! Good thing you did check them before using them!

author: james_s
author_rank: Super Contributor
timestamp: February 08, 2020, 06:45:58 pm
content: The delta is exactly it, voltage is the potential difference between two points. Think of a bird sitting on a power line, it could be said that the bird is "rated" for a few tens of volts and yet it is able to sit on a 7200V line without consequence. That example is not perfect since it represents an open circuit, but if you had a wire with say 7180V on it nearby, you could safely touch both of those and have just 20V across you as long as you weren't near earth.

author: olafwagner
author_rank: Contributor
timestamp: February 14, 2020, 12:21:02 am
content: My capacitors arrived today (after another lengthy wait), so I immediately replaced C821 as well as a bodge wire to replace the damaged pad. ('10a' & '10b' below) This went very well, and all the voltages are now in spec, and no more snaps, crackles and pops. Also, I noticed (for the first time today) that when I switch the scope off, the 2 Neon Lamps (that I mentioned in an earlier post) certainly flash a few times after the power is released, so I assume that is working precisely as designed.However, the scope still basically functions precisely as it did when I first got it, but after all this fiddling and measuring, I think that there are basically only two problems (which still may be related). I think apart from these 2 problems, everything else can be addressed with a good calibration. The problems are:#1 Trace IntensityI am still unable to get the trace to get the trace to disappear using either the INTEN pot on the front of the scope, or the INTEN ADJ trimmer inside. I have noticed that while the INTEN pot on the front doesn't make a significant impact on the brightness of the trace (it remains bright), it DOES have an impact on the retrace - interestingly when the INTEN pot is turned to the left (minimum), then the retrace is clearly visible dashing off to the left, however, when I turn the INTEN pot to the right (max), then the retrace disappears entirely. The HV rail measures at -1,831V so that is nicely within spec.As per my earlier post I need to figure out a way to test the diodes, but the fact that one can get the retrace to dissappear makes it seem like the unblanking (or is that blanking?) circuit is mostly working.#2 Trace is a 'Dash' and not a 'Dot' (in the X-Axis)The trace on the display is a dash - almost half as wide as a graticule mark, which you can see in '10g' below. This can be seen clearly when I slow down the trace, but even more so when I 'stop' the trace entirely in X-Y mode. (I intentionally used the flash for that pic because without it the trace look far more 'bloomy' than what it looks like in person)This is the issue that I more concerned about, and I fear that this is the reason why the previous owner of this scope gave up on it.My fear being that the problem is the CRT itself.While comparing the service manual for a similar Hitachi scope to mine, I see that they included scope diagrams for the X+ and X- signals (which as per my layman's understanding of CRTS are the ONLY thing that deflects the beam on the x-axis). In the case of the Hitachi, the X+ signal is a nice sawtooth, and the X- is a nice corresponding 'upside-down' sawtooth. I hooked up my cheapo-scope to the same 2 points on the horizontal PCB, and I got the exact same clean sawtooth ramps that I saw in the spec (I overlaid my scope images in attachment '10d' below).I then wondered about X-Y mode, and my fundamental assumption is that this bypasses the sweep gen and chopper circuits, and simply send the x-input signal to the CRT (after it has been attenuated and amplified). When I switched the scope to X-Y mode, I got a flat trace on my cheapo-scope even after I zoomed in a lot (to account for the noisiness of this digital scope's signal) and saw that the signal is flat. (refer to '10g' and '10h' below)Now the X+ and X- pins on the horizontal board connect directly to the CRT, there are zero components 'upstream'. This means that everything 'downstream' can be excluded from my problem (CH1 input, sweep gen, horizontal amp).I also hooked up my cheapo-scope to the 18v rail that feeds the HV transformer, so see if there is any ripple, but it also comes through totally clean.Conclusion (and next steps?)It is accurate to say that if a CRT gets the suitable HV input, and gets no signal on its X+,X-,Y+,Y- deflection plates, then it should show a 'dot' in the center of the screen right? Also, is the problem here the CRT itself, or can some of the HV circuits (the blanking circuit or HV amp) impact the trace?After a cursory browse on Ebay I see that there are used replacement CRT's available, but they are far more expensive than what I paid for this scope, and without being sure it is too risky.

author: olafwagner
author_rank: Contributor
timestamp: February 14, 2020, 01:11:00 am
content: Immediately after posting this I have one more hunch regarding 'Problem #2 - Dash vs Dot' in my prior post.When I turn the Horizontal position pot, the trace (or dash) move left and right very smoothly, which means that this is affecting the horizontal amp correctly, however, what if there is an 'imbalance' within the horizontal amp itself? What I mean is, assume there is a problem within the horizontal amp, would it not be theoretically possible that the X+ and X- values are not being amplified the same. If this were off, surely this would cause a 'broader' output rather than a dot?To test this theory I did the following test - now it is a bit unscientific, because all the values are relative (even more, they are relative to the impact of the horizontal adjustment pot) but I wanted to use this to illustrate:I flipped the scope into XY mode, and moved the trace to the center. Based on my prior post I know that there is a flat (constant) signal being sent to X+ and X-, so I decided to measure this with my DMM to see EXACTLY what was being pushed out of X+ and X-1. Center TraceWith the trace straddling the center division of the graticule, I measured these voltages (refer to 11a):X+: 93.4VX-: 83.8V2. Right TraceI then moved the trace so that it straddles the 4 divisions to the right of center, and got (11b, note that the green dash in the picture is merely a 'MS-Paint' illustration of where the 'dash' was):X+: 125.0VX-: 51.0V3. Left TraceI then moved the trace to the left so that it straddles 4 divisions to the left of center and got (11c, same note on MSPaint as above):X+: 61.8VX-: 114.6VWhile it makes sense that X+ increases (and X- decreases) as the trace moves further to the right, and vice-versa to the left, my question (and theory) is - maybe the voltages are too far out relative to one another (eg: when the trace is at the center, maybe the 2 voltages should be more similar in order to have less 'deflection'.Does this seem logical?If yes, I need to delve into the horizontal amp (schematic attached as '11d' below) and somehow compare what is happening in one 'half' versus the other to see whether any components that should be behaving the same are behaving differently.(Frankly it feels that I am grasping at straws here, but I don't know where else to turn).

author: AVGresponding
author_rank: Super Contributor
timestamp: February 14, 2020, 03:57:56 pm
content: It does seem odd that the voltages aren't symmetrical when the trace is centred. What about the Y deflection voltages? Are they symmetrical?