Hameg 203-6 Day 4

I assembled much of the front panel and tinkered around. I seem only to be able to get a trace under certain conditions. Although I now have a shape trace it is rolling and seems to be modulated. I know all the switches and potentiometers are dirty. this is adding to the confusion. So, I have packed the oscilloscope away for now.

When I have some switch cleaner and some more time I will try again. I would also like some way to test the old capacitors. I am thinking I may have to get the PCB out of the chassis to be able to access some components.

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Hameg 203-6 Day 3

My attention turned to the intensity and focus of the trace. looking at the circuit diagram and searching around the internet for ideas. I read some place that the high tension resistor chain is prone to have resistors going high or open circuit. Following up on this I found I did indeed have a resistor that had gone high in value.

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Hameg 203-6 Day 2

Having manage to get a faint blurred trace on my previous attempt at fixing this oscilloscope I figured on trying to increase the displays intensity and focus.

However I found even the faint trace to be very intermittent. I tentatively measured the heater voltage and it was getting the required voltage. The voltage rails on the oscilloscope are huge and would blow my cheap old multi-meter apart in an instant. I was shapely reminded of that when I slipped and gave a finger a quite zap, with a audible crack as something discharged into it.

With the power off I closely examined the PCB around the area of the CRT outputs, and I discovered what I believe to be the original fault. It looked to have been a manufacturing fault. A link wire that had been slightly bent over had missed the flow of the solder completely. Occasionally making enough contact with the bare copper pad and thus working from time to time. This is the most likely why the selector had been abused, trying to get a trace.

I had to solder it as best I could as I have not yet managed to find a way to remove this PCB without removing the transformer wiring.

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Hameg 203-6 Day 1

Long ago I bought 2 Hameg 20mhz Oscillosopes from eBay, most likely as a job lot spares or repairs, in the hope that I might make one good one out of the pair.

As it turned out they were not identical the other one is a slightly newer model 203-7. Fortunately that one does work, not perfectly but has been usable enough for my needs.

Both items have been sat in storage for years now, but my new found interest in my old hobby and profession necessitated my seeking them out and using on my multipurpose computer desk come work bench.

The 203-6 had never worked since the day I got it. As it is sitting there I recently decided to see if I could find the problem. Or more accurately problems.

The first was it had no trace at all and the trigger selector switch was sticky and had been poorly gummed in place by someone trying to repair it. I disassembled the and cleaned off the “hot snot” that had been applied.

The multi position selector had been abused and all the little notches were jamming. This must have been the case for some time and was the likely cause of the connecting support for the chassis being snapped. Hence the “hot snot” which looked to have been squirted in from the side without disassembly.

This did not completely restore operation but at the end of a long evening I did have a faint and very blurred trace.

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