Hello Guys, I scored an old Hung Chang oscilloscope that is not working and wondering if it can be fixed. When you turn it on there is no trace and all there is is a large out of focus dot hard left. No amount of adjusting fixes it. This also looks like its been attempted to repair before, there is new markings on the various sockets where the baords been taken out and solder points have been re soldered. All input voltages are correct.
Pretty much all the caps are done, either low capacitence, high (some very high) ESR and some up to 40% voltage loss. A lot of very suspicious solder joints.
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Some traces are even cut. Im not sure if this was from factory or someone troubleshooting:S So what are the chances of repair, and I cant find the correct service manual anywhere:S cheers. On a bit of chase to find Hung Chang manuals I found this dubious link: Clicking on it gives a 620 Kb zipped file that when unzipped offers a link to an 84 Mb Manuals file from cpgweb.net.
Options to Run, Save or Cancel. Looks suspect but if your antivirus is all up to date it could be worth looking at. Here's another for the 5504 of which it seems the 5510 is of the same series. You'll need the service manual to proceed far with this unless you've had considerable CRO repair experience but as you have something on the display you're a long way towards getting it sorted. Safety first. The scope does carry High voltage and proper discharge and safety technique must be used.
If you have not done it before, and not comfortable in dealing with it, then I suggest you ask a friend to help you out with the repair. I don't have the manual, maybe others have it. I search the internet but non is available also.
Many sites are virus and fake. Otherwise a bit of tracing is necessary. Vertical off the screen, can use the 'common moding' technique easier if you have the schematic. If you have a oscilloscope to trace the signal, it would be much easier to troubleshoot the scope. 'Visually' as long as the CRT is not meddled with, you should be checking the preamplifier and the vertical amplifier first. Clean the contacts and meddle with the front panel buttons would help, channel 1 or Channel 2, chop or invert etc. Without the Y, the trace should revert to somewhere center, but it would be easier if it has the 'Find trace' button like the Tektronix scope.
Without service manual or, at the very least, schematics, it seems difficult to repair this oscilloscope. It seems that there are multiple failures and even problems resulting from attempts at repair. Moreover, it is not a very common model.
If it were Hung Chang OS-620, that would be easy, I have already repaired several. But this model, I've never seen it.
One positive point is that there is high voltage. For the rest, it will be necessary to follow the usual principles: 1) check the supply voltages 2) repair bad contacts and bad solder 3) repair the damage of previous repair attempts 4) with the type of crt, check the pinout and measure the voltages of the vertical and horizontal deflection plates (Caution: there is high voltage on some pins of the crt) 5) Check horizontal and vertical amps in X / Y mode and repair them. 6) check and repair the focus and brightness circuits. (high voltage probe recommended) 7) check and repair the trigger and time base. But it is not possible to help you to do this from a forum.You will have to do a lot of reverse engineering.
Hey this is really good thanks, So here is some info for you All voltages are in XY mode and earthed to chassis. X - 57v and 84v Y - red- 104v.
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White 6.8v I have also taken a scope reading from the delay line going to the amp circuit. These were taken with the test signal on line 1.
1st pic was taken with position on max and second on minimum. Does this look out of the ordinary? This should help isolate witch side of the circuit is at fault. Both wires give same kind of reading but slightly different voltage levels. And also when the delay cord is removed sweep is dead center on screen. Cheers Sent from my iPhone using Tapatalk. Well done good progress.
You can adjust the center position and Gain later. If the 2 oscilloscope traces are from the delay lines and it can center the spot onto centre, means its looking very good. No rabbit hole.
You are getting close. You should be looking at page 3 of the schematic. Looks like the vertical amplifier is the problem then.
Edit: According to 60Mhz Hung Chang Scope, the 2 complementary output from the delay lines should be only 12mv Peak to Peak, both same. Is your scope accurate? Well, you can adjust the gain and center position later, so repair the vertical amplifier first. Well done good progress. You can adjust the center position and Gain later. If the 2 oscilloscope traces are from the delay lines and it can center the spot onto centre, means its looking very good. No rabbit hole.
You are getting close. You should be looking at page 3 of the schematic.
Looks like the vertical amplifier is the problem then. Edit: According to 60Mhz Hung Chang Scope, the 2 complementary output from the delay lines should be only 12mv Peak to Peak, both same. Is your scope accurate?
Well, you can adjust the gain and center position later, so repair the vertical amplifier first. Haha probably not, it is cheap. However if the signal is lets say 1v over total, wont i make all signals to high anyway? Also I tested the final CRT out put there is a small change in the square wave signal when i adjust vertical, but obviously not enough to center on screen.
In regards to the amp circuit, this is reaching the limits of my circuit analysis, but does the circuit supply the +/- independently or does it actually balance the 140v(?) between both poles? Sent from my iPhone using Tapatalk.
Warning!If you are not familiar with electronics, do not attempt to repair!You could suffer a fatal electrical shock! Instead, contact your nearest service center!Note!
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