hung chang 5510 oscilliscope repair

[The_Todd]

Could i have a bigger version of this, the pots on my board are labled different.

Cheers

[Armadillo]

Could i have a bigger version of this, the pots on my board are labled different.

Cheers

You mean the schematic?
size limit in this forum, so you can download here;

https://elektrotanya.com/hung-chang_protek_6502_04_06_20_40_60mhz_oscilloscope.zip/download.html

Wait for the display to say download.

[Armadillo]

Since lobed onto the positive side, so I think you should check the negative power supply.

no hurry, take your time and enjoy the fun [the puzzle someone set for you..... hahahaaha]

cheers;   

[The_Todd]

Ok this will take a while to digest. But so far I know a few things. 1. The CRT monitor seems to be fine 2. The problem apesrs to be the vertical signal circuit. This will narrow things down.

Now I notived on the schematics Ive got it uses 8v +/- as a reference voltage for the pots. Mine I think are using 12v any way of know knowing roughly what it is meant to be? And do all pots use the same referance voltages?

[Armadillo]

Ok this will take a while to digest. But so far I know a few things. 1. The CRT monitor seems to be fine 2. The problem apesrs to be the vertical signal circuit. This will narrow things down.

Now I notived on the schematics Ive got it uses 8v +/- as a reference voltage for the pots. Mine I think are using 12v any way of know knowing roughly what it is meant to be? And do all pots use the same referance voltages?

Should be OK as long as +12V and -12V, AND resulting in the DC bias to the complementary output is balanced [no lobe sided].

Digest the circuit and uncover why loped and check slowly while you enjoy it.

Cheers;

[The_Todd]

SHES ALIVE!!

and the fix was kinda embarrassing.

So after studying the Y signal circuit, I went and checked the voltages everything was ok, the pots were pretty much ok, and then spotted something weird, with the voltages right on the plug for delay curcuit.

So hell, why not give it a hard push down, and eureaka, so a bloody cold solder joint. Anyway, as you can see she works but there looks like a few more problems to tackle.... but we shall call it a night and repeat tommorrow.

Cheers!

[Armadillo]

 

[The_Todd]

Your mentioning that the voltages should be roughly equal, got me thinking, when i checked the circuit everything was a mirror so I just
Pinned down the voltage that was different 


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[The_Todd]

So now we have a heartbeat time to fix the brain and kidneys, this is very exiting having a working scope

as you can see in the pic it produces a fairly good wave, but I wont be able to calibrate anything more until I get the correct probes (only have 20mhz ones and replace the main capacitors.

Now if you see the second pic you can see how the other person tried to re-soldier the board it looks like he used a heavy rosin flux? Will this be an issue, as its all over the board :/

Cheers,


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[The_Todd]

Oh also anyone know what these sold for bacl in he day? Just curious.


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[Armadillo]

Oh also anyone know what these sold for bacl in he day? Just curious.


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I guess back in those days, oscilloscope should be expensive,, maybe... say... close to US$1000.00;   

if you are worried of the rosin flux, then clean it with IPA.

Cheers!

[The_Todd]

Oh also anyone know what these sold for bacl in he day? Just curious.


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I guess back in those days, oscilloscope should be expensive,, maybe... say... close to US$1000.00;   

if you are worried of the rosin flux, then clean it with IPA.

Cheers!

Well now i feel special, im more worried about the extra rosin damaging the tracks over time, I may have to completly de solder and resolder to be sure :/


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[The_Todd]

Ah bugger just realised this is actually missing a transformer cover near the HV cucuit. Will this cause any issues?


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[Armadillo]

Ah bugger just realised this is actually missing a transformer cover near the HV cucuit. Will this cause any issues?


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2 frame of thoughts, for one is the protection from physical contact, example the safety aspect and for the other is the noise/spike screening "BUT" if so then the other side of the PCB should also be screened isn't it. So I reckon more on the former thought, but not sure really. Wonder if you build a cover yourself, will it drop out and cause a short circuit?  LOL!
Maybe you can call the former guy and ask it from him.

[The_Todd]

Ah bugger just realised this is actually missing a transformer cover near the HV cucuit. Will this cause any issues?


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2 frame of thoughts, for one is the protection from physical contact, example the safety aspect and for the other is the noise/spike screening "BUT" if so then the other side of the PCB should also be screened isn't it. So I reckon more on the former thought, but not sure really. Wonder if you build a cover yourself, will it drop out and cause a short circuit?  LOL!
Maybe you can call the former guy and ask it from him.

Haha if I knew who the former guy was My job would not be this hard. I was thinking more or magnetic interference ect. But yeah cant be that hard to make one... 


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[tautech]

Ah bugger just realised this is actually missing a transformer cover near the HV cucuit. Will this cause any issues?


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The cover there is primarily for protection while making adjustments but in saying this some scopes don't have covers on the EHT or PDA. The EHT is created with a simple SMPS running ~30-50 KHz and the PDA is essentially HV DC.
I'd move ahead and use the scope with the knowledge there might be some EMI or maybe not. Suck it and see.