Hameg HM203-5 scope retrace fault

[Guineafowl]

This circa 1990 scope has started to display a retrace line when handling a sine wave. It’s only visible on the left 1/4 of the screen. The fault doesn’t appear when the square wave cal is used.

Looking at the block diagram, and from initial thoughts, I’m guessing the blanking signal must be present, but is fading out too quickly and letting the beam through just before the start of the next sweep.

Since the scope is quite old, I think I’ll give it a service soon, including:
1. Contact cleaner for all switches.
2. General cleanup and inspection of soldering and connectors.
3. Recap.

If the fault persists after the service, I’ll start looking into it then. Is this a sensible approach, or does someone know straightaway what might be wrong? I don’t know how common a fault this is. Could the scope be damaged by using it in the meantime?

 

[Averagesupernova]

Best bet is another scope to troubleshoot the one you have. Looks to me like an excellent opportunity to gain some troubleshooting skills. I doubt you will damage anything running it this way. Does it make a difference what the sweep rate is?

 

[Guineafowl]

Best bet is another scope to troubleshoot the one you have. Looks to me like an excellent opportunity to gain some troubleshooting skills. I doubt you will damage anything running it this way. Does it make a difference what the sweep rate is?

Yes, the retrace line alters according to the sweep rate - shorter on a faster sweep. At some speeds, there’s a vertical line at the start of the sine, as if the sweep is jamming at the start.

 

[Averagesupernova]

That vertical line will likely change based on how you have the trigger set. It is supposed to hold until the trigger initiates a sweep. If it is not blanking you will see something vertically because you have a signal in the vertical section.

 

[Tom.G]

1. Contact cleaner for all switches.

Be cautious about using contact cleaner at the input circuitry. Tektronix specifically warns not to use contact cleaner there because it degrades the PC board material used.

 

[Averagesupernova]

Be cautious about using contact cleaner at the input circuitry. Tektronix specifically warns not to use contact cleaner there because it degrades the PC board material used.

I tend to go: If it ain't broke, don't fix it. In other words, if none of the switches seem noisy, leave them alone.

 

[Guineafowl]

OK, thanks. The switches are a bit finicky, especially the component tester toggle and on/off. I was going to spray in a tiny amount, under guard of a paper towel, and work the switch.