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Mac SE CRT ghosting/Bleeding to the right

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    #16
    Originally posted by ivannudem View Post
    Thanks for everybody's help. I will proceed with extreme caution and discharge as it is advised. I have watched several youtube video and understand where to hook the clip to. I'd better put in series a MΩ resistor to keep the initial current low enough not to damage the ground. Anyway, to recap the Analog board, I'd need to discharge it too, I really want to get this streaking problem fixed because I've spent too much money and my time into it, cleaning the Floppys + cleaning the outer shell took me totally 8-10 hours, don't want to abandon it. But I live in a relatively small city in Canada, where there're not a lot of vintage computing enthusiasts, let alone CRT TV repair shops, so it's difficult to have someone fix it, I'll have to do it myself. hopefully the SE doesn't have SMT capacitors, so recap should be within my skills.

    Thanks
    Yes good, use the resistor if you feel compelled to discharge the CRT , for example if you have to remove the anode cap or disconnect the CRT's external aquadag connection from the set's ground.

    If you come across SMT capacitors, the easiest way to remove those, without other special tools, or risk to the pcb tracks, is with two soldering irons, one in each hand, melt the solder on each connection at the same time. Adding extra fresh solder often helps, then clean up the pads with solder wick & IPA or similar cleaner.

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      #17
      Originally posted by ivannudem View Post
      Anyway, to recap the Analog board, I'd need to discharge it too
      There is enough parasitic resistance on the analog board to discharge all of the caps on it. Plus there's no high voltage besides what's inside the fence around the flyback transformer, so steering clear of that you will be fine.

      You also MUST recap the power supply, it's in its own metal enclosure screwed to the bottom of the analog board. The capacitors in it can get very bad and cause all sorts of headaches.

      Originally posted by ivannudem View Post
      hopefully the SE doesn't have SMT capacitors, so recap should be within my skills.
      There are no SMD capacitors in either the SE or SE FDHD. But you need to be VERY careful when recapping the logic board because the through-hole VIAs that the axial capacitors are soldered to are very delicate. It's super easy to pull a VIA out of the board and then you have a very difficult problem to fix. Axial capacitors are also getting pretty hard to find these days, so you may want to use radial capacitors instead. You can just fold the legs out at 90 degree angles from the capacitor body and another 90 degree angle to go into the board.

      Recapping the entire SE (analog board, PSU and logic board) is quite a number of capacitors. Looking at the BOM for the last SE I did, it was about $60 in parts, the most expensive being the PSU's main filter cap, which is an odd size and hard to get. I ended up having to modify the mounting points on the PCB with a drill because the original spade type cap was no longer available. The other hard to find cap is the 3.9uF horizontal deflection capacitor, this is a high frequency rated capacitor and is unobtanium. You'll have to substitute a special high frequency metal film capacitor like this one:

      https://www.mouser.com/ProductDetail/667-ECW-F2395JA

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        #18
        Thanks again for everyone's generous help and precious advice.

        Comment


          #19
          Hi, Just an update, I recapped the problematic Mac SE's analog board (changed all electrolytic caps bought from digikey), but the problem still persists.

          https://imgur.com/a/gJ4QRkP

          Recap the analog board doesn't make any changes, except making the max brightness a little bit brighter... But under the max brightness, I did find the horrible phenomenon that even the whole large area to the right of a vertical black line will bleed as gray color to the right, which is the symptom of the unfortunate SE 30 mentioned on this forum and 68kmla (where he found the problem was the CRT)
          https://68kmla.org/forums/topic/6064...-to-the-right/

          https://imgur.com/a/ROddjRf

          I don't know what to do, but recently I picked up another SE FDHD from a friend, the CRT was perfect without problem and after recap of the analog board with the same batch of new capacitors. So i'd assume that it was the problem of the CRT. But I'm just curious, how could a CRT itself has such a failure mode?

          I did find that the CRT's neck has a pinkish indicator which indicates that it has some leakage? After the same recap process, this troublesome CRT was dimmer than the FDHD's when both are at max brighness, so does this has anything to do with aging, i.e. less electrons resulting in the bleeding to the right?

          I also touched some old solder joints on the AB if I find that they are old and oxidized, but no apparent soder joint cracks, and used IPA to clean the tuning pots (of brightness and focus)

          Any suggestions?
          Thanks

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            #20
            I also find something strange about this troublesome CRT, when powered up (to the screen prompting inserting floppy disk (it doesn't have hard disk)) , the right edge of the screen is more dark/bluish than the left part, it's hard to catch by a camera because my phone seems to automatically adjust the exposure of the img.

            https://imgur.com/a/AzPfwNN

            But the good one (FDHD) i got seemed to be OK, the contrast of this FDHD's CRT is also different than the bad SE, it seemed more blackish than bluish, where can I tune the tone of the screen?

            https://imgur.com/a/Sdr9zn4

            I also noticed some other compact macs on sale on ebay which have this kind of bright streaking and black smearing problem, this might have been a common problem of this CRT,
            https://imgur.com/a/Rc2GNuE

            Apart from recapping the AB, reflowing suspicious solder joints (which have been performed), how can I improve the streaking problem of the SE without buying a new used CRT? Does this means that it has approached its end of life?

            Thanks

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              #21
              The last time I've had to address horizontal smearing to the right it was a completely tube driven set. It can be an issue in the sync separator/AGC circuit or low anode voltage. I have also seen it in tubes with very, very high hours. This however is a solid state analog board, so I got no idea where to investigate.
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                #22
                Hi, NeXT,
                Thanks for your suggestions, I also suspect there was a problem of the tube, maybe it has very high hours of usage and had been worn out. Because comparing with my SE FDHD, when the brightness knob (on the front panel) was turned to the maximum, it was not very very bright, whereas the FDHD was really bright even shining to the eyes (both of the SE and SE FDHD’s brightness pots on the analogue board were at about the same position, around the middle...)

                ironically the FDHD has more/darker menu bar burn-in whereas this troublesome SE CRT has less burn-in on the top menu bar area.... maybe burn-in is not a good meter to measure the hours of usage LoL... I really hoped that CRT manufacturers installed some kind of mileage meter like cars, so that second hand buyers to assess its remaining life and value....

                also I may suspect the life of flyback Transformer, if it is too old, it may not generate enough voltage... but ironically the flyback’ sealing epoxy (the brownish thing, don’t know what it is called) was lighter than the good FDHD’s, so maybe the browness of the seal is not an indicator of flyback running hours either...
                so this dimmer SE CRT was caused by either the remaining filaments Itself or an aging flyback....

                I do not want to invest more on this troublesome SE, but I did spend time to clean the 2 floppy drives, recap its AB, I don’t want to throw it away, but the smearing is really annoying, and seems to appear on many of the compact macs (the SE30 I linked before, and other SEs I saw online) the best chance for me is to wait on local Craigslist to see if someone has a broken SE, Plus, early Classic as donner machine to sell me the tube LoL... (I know there’s a compatibility issue about the classic screen with this SE) buying from eBay +shipping is expensive ....

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                  #23
                  I have been working with CRT's since the early 1970's, I have designed & built many video monitors and TV's with them and have nearly all the books relating to TV and scope CRT design going back to the 1920's, in my library, that I have thoroughly studied.

                  I can say that not a lot of what has been posted on this thread makes any sense. The smearing effect to the right, in the direction of scan progression, is not generated by any kind of CRT defect. (perhaps, one exclusion see below under Heater-Cathode leakage topic).

                  Generally, the fault of defective high frequency video response (smearing to the right) is caused by an abnormality in the frequency response of the amplifiers driving the CRT, not the CRT itself.Or a corruption of the frequency response where the video signal is formed initially.

                  Video amplifiers drive either the grid or the cathode of the CRT according to the particular design of the VDU or TV.

                  In the case where the cathode is being driven, if CRT heater to cathode leakage develops, this is about the only way a CRT defect in itself could produce the smearing effects discussed on this thread, and that is a moderately rare event. If it did happen, it is fixable by adding a CRT heater drive transformer with a low secondary capacitance.

                  Blaming the CRT itself is for this fault, I think, is barking up the wrong tree most likely. But to confirm this was the case for sure, I would have to have one of these defective units on my bench in front of me and go through it using my test generators & the scope.
                  Last edited by Hugo Holden; June 2, 2021, 02:38 AM.

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                    #24
                    Originally posted by Hugo Holden View Post
                    I have been working with CRT's since the early 1970's, I have designed & built many video monitors and TV's with them and have nearly all the books relating to TV and scope CRT design going back to the 1920's, in my library, that I have thoroughly studied.

                    I can say that not a lot of what has been posted on this thread makes any sense. The smearing effect to the right, in the direction of scan progression, is not generated by any kind of CRT defect. (perhaps, one exclusion see below under Heater-Cathode leakage topic).

                    Generally, the fault of defective high frequency video response (smearing to the right) is caused by an abnormality in the frequency response of the amplifiers driving the CRT, not the CRT itself.Or a corruption of the frequency response where the video signal is formed initially.

                    Video amplifiers drive either the grid or the cathode of the CRT according to the particular design of the VDU or TV.

                    In the case where the cathode is being driven, if CRT heater to cathode leakage develops, this is about the only way a CRT defect in itself could produce the smearing effects discussed on this thread, and that is a moderately rare event. If it did happen, it is fixable by adding a CRT heater drive transformer with a low secondary capacitance.

                    Blaming the CRT itself is for this fault, I think, is barking up the wrong tree most likely. But to confirm this was the case for sure, I would have to have one of these defective units on my bench in front of me and go through it using my test generators & the scope.
                    I can agree with this. I didn't work on CRT's for very long (and am only 34 years old for that matter and didn't start working till 200, but this is true. Smearing to the right is generally not the CRT. People assume this from old transistorized TV's when the CRT goes weak because they crank up the contrast to make it brighter and it smears. That isn't from the CRT though. Yes, the CRT is weak and needs to be cranked up, but that's saturation in the transistor logic. Tube based TV's didn't do this, instead when a CRT gets weak, you see a weird posterization of the picture, like it's going silver and glimmering. (At least on black and white sets, which I fool around with for fun).

                    In this case, it very much seems like a high frequency issue, or even possibly a bad ground. I've seen badly grounded VGA cables do this to LCD's as well, same effect smearing to the right.
                    IBM PS/2 Model 25, NEC V30 8MHz, 640KB RAM, ATI VGA Wonder XL, 2GB SSD, Ethernet, DR DOS 6/GeOS, Xircom PE3 Ethernet

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                      #25
                      One great thing about a CRT, it does actually do a good job of showing what is wrong with the frequency response of the amplifiers that are driving it.

                      This shows up, if there is a defect on a black to white signal transition, or a white to black transition, not as easily seen unless the CRT's brightness is elevated.

                      The defect though, is there to be seen on the black to white transition, of the picture content.

                      however, when the video signal transitions from white to black, if the signal overshoots, more into black, you cannot see it of course, because the CRT's beam is already cut off in most cases.

                      To see the defects in the video amplifier processing system (and to isolate and repair them) requires that the video amplifier is driven with square waves and the frequency response (the quality of the square wave reproduced) is assessed on a good scope, like a Tek 464,465,466 or 2465B.

                      Then you would see that the video amplifier frequency response of your monitor is abnormal, as there would be overshoots after the fast rising edge (or fast falling) of an applied square wave test video signal from a generator. Though some suitable computer graphics work just as well as a test signal.

                      I have attached an image of part of one of those Imgur images posted (that my computer struggles with).

                      If you look you will see on your image, that one scanning line, that if the video signal has been near black (or a low beam current value) for a while and then it transitions to white, there is a whiter than white overshoot, or a "smear" characteristic of a defect in the frequency response of the video amplifiers.

                      Where is this defect ?

                      Who can say at the moment, as I have not seen the information required to isolate it. This is the schematic, and scope recordings of the signals at points on the circuit, as the signal passes through the video amplifier stages. If I had the schematic, and a scope on the circuitry, it would be dead easy to show where the problem was occurring.
                      Attached Files
                      Last edited by Hugo Holden; June 3, 2021, 08:54 AM.

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                        #26
                        Hello to every expert, Thanks for all of your suggestion. I do agree that the chance of a CRT failure is rare, but it did happen as in this post (https://68kmla.org/forums/topic/6064...-to-the-right/)
                        as I quote:
                        "Sadly recapping the Analog board didn't show any results, horizontal image still collapses weirdly on reset and there still is bleeding/ghosting to the right.
                        All caps (Samyoung branded) measured reasonably within spec (all capacitance values are met higher then spec, ESR was a bit up but nothing that shocked me...)
                        "

                        "CRT swap didn't have the issue, so its either the CRT itself or the cables to it...
                        Can anyone explain this behaviour of the CRT? I don't understand how the tube itself can cause this to happen"

                        I have replaced all electrolytic capacitors on the analog board, as suggested in this diagram (https://imgur.com/JhQwNvK), but not the ceramic ones, nor any resistors, ICs, transistors...

                        I found a SE/ SE-30 Analog board Schematic online, could somebody help me point out which specific part/component is possibly causing this problem?
                        https://imgur.com/a/eBipQLz
                        I don't have a scope, just a multimeter, so what I can do is just shotgun changing components....

                        And as for the possibility of a bad grounding, I did check the continuity of the power cable to the analog board, every line is conntected, and the solder joints of the connector have been reflowed, the PSU's extra ground wire (not sure what it is called, the green extra wire extending from the PSU metal case) has also been firmly screwed to the metal chasis. the other FDHD which is in even poor cosmetic and electronical conditions plugged in the same power outlet without problem, its PSU cable has been badly dammaged, my friend saved it from a scrapping/recycle center, and some of the cable's wire skin has been shoved by knife, exposing the metal wires, I used some insulation tape to wrap them, they work OK. The cables in this "bad" SE are intact from visual inspection and the connectivity is fine, I didn't mesure the resistance of the wire comparing to known good one, since I don't have another set of PSU cables of this type...But I assume the grounding is OK.

                        Thanks
                        Last edited by ivannudem; June 3, 2021, 01:21 PM.

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                          #27
                          Originally posted by ivannudem View Post

                          I found a SE/ SE-30 Analog board Schematic online, could somebody help me point out which specific part/component is possibly causing this problem?
                          https://imgur.com/a/eBipQLz
                          I don't have a scope, just a multimeter, so what I can do is just shotgun changing components....
                          The circuit you posted: https://imgur.com/a/eBipQLz is of the horizontal and vertical deflection (scan) stages and the EHT generator and CRT's grid voltage supply. The fault causing your problem is not in this part of the circuit.

                          It is the circuit that provides the video drive to the CRT's (most likely cathode) that we need to see.

                          As I mentioned in a previous post, an exception where the CRT can contribute to an abnormal frequency response, is in a case where the video drive to the CRT is at its cathode, and heater cathode leakage in the CRT's gun. It is relatively rare and if it does happen, there is a work around by running the CRT's heater from an isolated supply. But, most likely the fault is in the video amplifier driving the CRT's cathode and not the CRT.

                          Unfortunately, for this type of issue, not having a scope to look at the video signal makes things very difficult.

                          Most video amplifiers in VDU's are wide band amplifiers and should have a flat frequency response from a very low frequency, 30 Hz right up to over 5MHz, some better monitors up to 8 to 10MHz. (A typical analog TV usually only makes it to 5 or 6 MHz). In Computer VDU design there is often more attention to the video amplifier high frequency response, this is how they can display super fine detailed graphics in a monochrome VDU. In color CRT's the resolution becomes limited by the geometry of the shadow mask and phosphor dot pitch, rather than the bandwidth of the gun amplifiers.

                          Comment


                            #28
                            Hi, Hugo, Thanks a lot for your help. I see, the problem is on the small board, (called video board/ neck board?) which is connected to the rear neck of the tube. I didn't find any related schematic online, but I did find a photo from 68kmla:
                            https://imgur.com/a/etf4Xvo
                            It seems its relatively simple, composed of several diodes, resistors, ceramic caps and one 2N3904BU NPN transistor...
                            this photo was from the 68kmla post found here:https://68kmla.org/forums/topic/2381...ions-and-se30/

                            It says that there are pretty common problems of the neckboard with this transistor which will result in the shown inclined scan lines problem... (I don't know how to describe it, see the above pic)...
                            But my problem is the smearing to the right problem....should I suspect this NPN transistor or the ceramic caps and resistors on this small board?

                            Interesting enough there's another post in this thread, where the person used to have the tilted scan line patterns and after changing the NPN transistor, the CRT finally displayed the desktop but he got the smearing to the right problem:
                            https://68kmla.org/forums/topic/2381...comment-668071
                            also in screenshot here:https://imgur.com/a/DcX1TlS
                            So there must be some other components (ceramic caps, diodes?) failing on this video driver board causing this...

                            Really big thanks for your advice, so the issue is now (at least with very high confidence) located on the small video/neck board.... upon checking the photo of the neck board, could you please tell me which components are most probably faulty (this transistor? Diodes? Or ceramic caps?)Thanks.

                            PS. I just want to add something about the possibility of “overdriven Contrast”, this CRT seems to be old and dim, compared with the other FDHD I had. I mean there’s an internal pot controlling “cutoff/brightness” on the analog board. Both of the 2 machines have this pot set to about the same middle position, but on this bad SE, the front panel external “contrast/brightness” needs to be tuned to its highest/last 1/3 range to make the raster/image visible, whereas the good FDHD only needs the External contrast knob to stay at around middle to get descent bright pictures... but even tho the contrast of the bad se is set to the Highest 1/3 range, i didn’t see any retrace lines or faint overbrightened pale image, so I assume it is not overdriven that caused the smearing... But I did notice that if I turn the contrast knob down, to first 1/3-1/2, the smearing seemed disappear, but the screen got very very dim, just barely a little bit brighter than barely visible,unable to use it in that setting...
                            Last edited by ivannudem; June 3, 2021, 09:41 PM.

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                              #29
                              When there is a frequency response issue in the video amplifier/CRT gun driver, it will always seem less severe at low contrast and low brightness levels.

                              It is pretty difficult to make any helpful suggestions, without the schematic of the CRT neck board and he circuit that feeds that from the main board.

                              Comment


                                #30
                                Schematics for macs is spotty. Some models got most of a complete set (the early compact macs especially) while later models have almost nothing. Most repairs are shotgun jobs or through years of other people shotgunning the same parts and building a relatively "accurate" list of parts known to fail and replace. That often is worthless when it's a fault that isn't a regular fault.
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