Hameg 203-6 No focus response from control knob

Thread Starter

Norrissheldon

Joined Dec 28, 2018
3
Hi all, my name is Norris and I live in South Wales. Just returning to destroying components after a lengthy absence and I purchased a Hameg 203-6 oscilloscope that was sold as not working because it does not focus, there is no response to the knob being turned.I have downloaded the page of the circuit diagram that shows VR402 connected to input G3 on the CRT. Before I start taking it further apart has anyone come across this problem before or have any constructive advice to offer please?
 

bertus

Joined Apr 5, 2008
21,861
Hello,

As far as I can see there are quite some resistors connected to VR402.
When one fails, the focus will not work.
Also when one of the three capacitors in the circuit fails, there will be focus problems.

HM203_focus_circuit.png

Bertus
 

Thread Starter

Norrissheldon

Joined Dec 28, 2018
3
Hello,

As far as I can see there are quite some resistors connected to VR402.
When one fails, the focus will not work.
Also when one of the three capacitors in the circuit fails, there will be focus problems.

View attachment 166745

Bertus
Thank you, I spent half an hour online looking for that drawing :). I did however find this resistor which appears to be open circuit.
 

Attachments

bertus

Joined Apr 5, 2008
21,861
Hello,

The schematic part I posted was from the HM203-7.
The numbering of the parts is different in that one.
I have also downloaded the HM203-6 schematic.
That resistor IS part of the focus circuit.
It is a 221K resistor:

HM203_6_focus_circuit.png

Bertus
 

Thread Starter

Norrissheldon

Joined Dec 28, 2018
3
Hello,

The schematic part I posted was from the HM203-7.
I have also downloaded the HM203-6 schematic.
That resistor IS part of the focus circuit.
It is a 221K resistor:

View attachment 166779

Bertus
Yes, after I posted my reply I realised that the image you had posted was not the same as the one I found in the online manual. Tomorrow I will attempt to replace that resistor and see how I do. Removing the board so that I can get to the solder side is going to be challenging. Thank you very much for responding.
 
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