hung chang 5510 oscilliscope repair

[The_Todd]

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. 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,

[Zucca]

it will be a long journey. Good luck.

[Armadillo]

A simple push-pull horizontal amplifier to CRT coil around block Q801 to Q812?  if I can remember correctly. Just probe for the sawtooth waveform and DC supply voltage [140V?]
Hope it helps.

[tautech]

On a bit of chase to find Hung Chang manuals I found this dubious link:
https://wiggstanwebpha.jimdo.com/2017/04/13/hung-chang-oscilloscope-manuals/

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.
jaboxajimosej.tk/9143744/894c9d47-hung-chang-5504-manual-412aecc06


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.

[The_Todd]

well, that's interesting Q801 a utc4558 has pin 3 un-soldered by the looks of it, by the last person who fiddled with it.  when I connect it, the dot disappears, disconnect it and the dot comes back and even does a single right sweep then dissapears.

This rabbit hole looks deep.

[Armadillo]

well, that's interesting Q801 a utc4558 has pin 3 un-soldered by the looks of it, by the last person who fiddled with it.  when I connect it, the dot disappears, disconnect it and the dot comes back and even does a single right sweep then dissapears.

This rabbit hole looks deep.

The front trigger knob, set to click and put to auto first, otherwise it may not trigger.
Also base of Q801, probe is there sawtooth entering base?.
Either the sawtooth Gen or the horizontal amplifier or simple still, the trigger knob not properly set to auto.

Please use probing and measuring, don't use rabbit hole.   

[The_Todd]

ok, no saw tooth, just static, according to my cheap DIY scope. chips is getting 23v and it it amplifying..something....
thats by check bot the input +/- of both sides of the chip

[The_Todd]

Also the trigger light is going off now and then if thats any good info for you haha

[Armadillo]

It would be good to get the basics done up first;

Clean all the mechanical contacts with contact cleaner.
Set Sweep mode to Auto
Set Source to CH1;
All knobs to detent positions.
All pull knobs to down position.
Sweep to 5us/div, shake abit.
Try horizontal sweep mode 'A' and then 'B'. [there are 2 sweeps gen]

Most of the time, the contacts are dirty.

After that check that sweep A and Sweep B are pulses available.

[The_Todd]

It would be good to get the basics done up first;

Clean all the mechanical contacts with contact cleaner.
Set Sweep mode to Auto
Set Source to CH1;
All knobs to detent positions.
All pull knobs to down position.
Sweep to 5us/div, shake abit.
Try horizontal sweep mode 'A' and then 'B'. [there are 2 sweeps gen]

Most of the time, the contacts are dirty.

After that check that sweep A and Sweep B are pulses available.

Ok next day off ill give it a serious clean out,
It looks like its hard a hard life, but a dual 100mhz may still be worth the effort 

[The_Todd]

Ok so an update, Ive been reading lots of forum posts and guides and found somthing interesting.
If i turn the lights off, put intensity up high you can see a glow, and there is fact a sweep left to right and it chnged speed with division change. I think its sitting above the visual screen. And when you turn off, then on again there is a single sweep in the middle of the screen.

At least I know shes alive

[Armadillo]

Ok so an update, Ive been reading lots of forum posts and guides and found somthing interesting.
If i turn the lights off, put intensity up high you can see a glow, and there is fact a sweep left to right and it chnged speed with division change. I think its sitting above the visual screen. And when you turn off, then on again there is a single sweep in the middle of the screen.

At least I know shes alive

So the picture with the stationary bright spot in the middle is not longer valid? In that case we should be looking at the vertical. Its the vertical knob able to adjust the trace down. Can you ground the channel input and adjust the vertical knob to move down the trace?

[The_Todd]

Yes, I for got to mention I resoldered Q801 properly onto the board wich sloved the sweep problem.

I tested in sweep mode and x-y mode and no change at all to vertial even when grounded or knobs adjusted on both channels. It is literly stuck.

[Armadillo]

Yes, I for got to mention I resoldered Q801 properly onto the board wich sloved the sweep problem.

I tested in sweep mode and x-y mode and no change at all to vertial even when grounded or knobs adjusted on both channels. It is literly stuck.

I don't understand if you can test the sweep in x-y mode.?
I thought you will need input into both the X and Y to operate in that mode?

[The_Todd]

So, in normal mode I can see  the sweep (wich is just a glow moving across) , but i put it in X-y so the "dot" stayed still, wich would make it easy to notice any sudden movement. But in any mode, there was no vertical movement using grounding, test signal or vertical adjustment.

[Armadillo]

So vertical should be much simpler than the horizontal right?
apply the calibration square wave into the channel input and trace the signal along the vertical amplifiers should be the way to go.
check IC 2? for the signal output [ch1].

Edit: It's better to visual that the CRT vertical coil is not messed up by the original user, also check the connectors..

[The_Todd]

Hey still haven't had a chance to re test.
i REALLY wish i could find a 55xx series manual, as these are quite different layout to other models, and also to check all these pots in case they were adjusted :S and tracking back the amp signals is a bit of a jungle.

how do i check the CRT coil? also if i disconnect the Y wires, will this theoretically bring the sweet to the center (if it is safe)

cheers,

[Armadillo]

Hey still haven't had a chance to re test.
i REALLY wish i could find a 55xx series manual, as these are quite different layout to other models, and also to check all these pots in case they were adjusted :S and tracking back the amp signals is a bit of a jungle.

how do i check the CRT coil? also if i disconnect the Y wires, will this theoretically bring the sweet to the center (if it is safe)

cheers,

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. 

[tautech]

Another look finds these are also sold as Protek so identifying the model # Protek might help you find the manual.

[oldway]

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.

[Armadillo]

See the Hung Chang generic block diagram of the vertical, should helps you in tracing the circuit.

Also attached the schematic of the Hung Chang scope, though it is not specifically 5510, but should give you a better guide to start tracing..


Hope it helps;   

Edit: See page 1 of the schematic, you can see signal routing through those selector switches, now isn't it a good place to start probe for the signal?

[The_Todd]

See the Hung Chang generic block diagram of the vertical, should helps you in tracing the circuit.

Also attached the schematic of the Hung Chang scope, though it is not specifically 5510, but should give you a better guide to start tracing..


Hope it helps;   

Edit: See page 1 of the schematic, you can see signal routing through those selector switches, now isn't it a good place to start probe for the signal?

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. 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


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[The_Todd]

And to add more data on stationary.XY mode with no input. The voltages on delay line are

White -0.947v
Red  +0.536v (however red was not stable and kept creeping up)


Sent from my iPhone using Tapatalk

[Armadillo]

And to add more data on stationary.XY mode with no input. The voltages on delay line are

White -0.947v
Red  +0.536v (however red was not stable and kept creeping up)


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.

[The_Todd]

And to add more data on stationary.XY mode with no input. The voltages on delay line are

White -0.947v
Red  +0.536v (however red was not stable and kept creeping up)


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.

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?


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