Hameg 203-5 Osciloscope Problem - How to repair?

[sidnit33]

Hello guys, this is my first post, I am new on the forum. I have a bought a Hameg 203-5 for 50€ and i am having something of an issue, on the video I feed an aprox. 400 Hz signal, Automatic triggering, and there is an vertical line to the left when i fed the sinus signal (is this normal?), and starting at 5ms time/div an extra horizontal signal appears.. any ideas how to fix it?

Link to the service manual: http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Hameg/hm203-5.pdf

[shakalnokturn]

Without saying it's the cause for your fault, it's very common for the switches in the timebase section to cause problems.

[BFX]

Hi, I think you have problem with blanking circuit.
Try to check triggering of blanking and stuff around.
But first of all power supply lines voltages and ripple.

[capt bullshot]

This signal isn't wide enough also, maybe some internal power supply voltage too low.

[sidnit33]

thank you for your answers!

I checked voltages in the TB-Board +12V, +5V,-12V and +170V are inside the 5% Tolerance.
Right now I don´t have a second oscilloscope to check the ripple, so at this moment I am figuring out how to check the blanking part, any ideas?

I've order a  contact-cleaner spray so next week i will be cleaning the switches, i really want to have a nice oscilloscope to begin with my own home-lab.

The signal is not wide over the whole screen because of the X-mag/x10 switch, when pressed it makes the signal wide.

[shakalnokturn]

I have a couple of HM203-6's one I have been using intensively for 20 years now and it wasn't new when I bought it.
I serviced it about 7 years ago and it's time I went to the trouble again as it's showing similar symptoms to yours (at least the one that looks like a blanking problem) on some Time/Divs.
Checking PS voltages (and ripple?) was a good idea in any case, but before spending hours in intensive troubleshooting give (almost) everything that moves in there a good spray and manoeuvrer it a dozen times. Don't forget the Time/Div setting as most of your troubles will be there... It is hard to get he spray into that. Avoid spraying variable capacitors though!
I recommend tightening all the power components on the rear heatsink while you are in there.

The other problem (well I did say everything that moves!) is the Piher trimpots, the brush contact can get really crummy with age and I wouldn't be surprised if your horizontal amplitude weakness came from there.

You don't necessarily need to replace the trimpots usually, a good spraying and working usually does the trick but you'll have to go through the calibration if you want a decent scope.

[BFX]

Do you have another oscilloscope? Do you have HV probe? Do you have isolation transformer?
Be careful around there lot of high voltages are present in this area.

Blanking part is here. (see pic)

[sidnit33]

Hello and thank you for your feedback. I am taking this oscilloscope as a Project, my idea is to understand how it works, service it, if possible get it to a better condition and most important learn on the process. I don't have money for a Rigol DS1052E, but in the next years that could be the next step for me.

I notice my oscilloscope has been serviced before, 3 things caught my eye:

1- black plastic cable tie repair (see picture)
2- condensator 8.2 on the under side of the TB-board (see picture) (Not sure if this is factory original or added later)
it connects a pin of the flip-flop SN74ls74an to a bc237
3- I noticed a resistor that may had been changed on the XY-Board, it measures 56.5 ohm (see picture), near the resistor the text handwrited, 51,1 ohm, (i think this is not so important).
===============

I measure the voltages on the TB-Board against chassis:

Reference: Multimeter DC V

Y-Pl- +3.75 V -> + 3.8 V
+140 V -> + 144.8 V
+170 V -> + 173.2 V
+5 V (-12V antipole) -> - 6.5 V
+24 V -> + 24.3 V
+ 5 V -> + 4.95 V
-12 V -> - 11.84 V

I took some precautions for the measurement
- Unplug Oscilloscope and wait
- Connect Multimeter
- Remotly swithching AC
- Repeat

I am wondering why am i getting -6.5V on that control point, or if i am measuring it right against chassis, not sure if i should get +5V or -12V.

===============

On the YF-02 Board i noticed two resistors that are shattered! both measure 560 ohm, so they seem to work ok (see picture)

===============

I don't have an HV-Probe and i have easy but limited access to a second oscilloscope at my workplace (a bit far away to carry my oscilloscope there).
I'm definitely planning to find an isolation transformer for my home-lab, i am still giving it a thought on how much power do i need, but at the moment don't have one.

===============

I didn't find on the documentation what the Checkpoint 5.5 V_pp on the TB-Board means (See Picture). Has it something to do with the blanking?

Thank you!

[shakalnokturn]

The resistor in your last photo (R817) often gets blown along with F800 and VR87, due to using the "component tester" on too high voltages (i.e: discharging SMPS bulk capacitors). The HM203-5 was quite weak in this respect, the HM203-6 much better.

[BFX]

I didn't find on the documentation what the Checkpoint 5.5 V_pp on the TB-Board means (See Picture). Has it something to do with the blanking?

I don't think so, it's look like sweeping signal.
HV probe would be very useful here because I seen lot of troubles with high voltage supply on this type of scope.

[markce]

How is your X-position setting? Is it in middle position or very much to one side? If so, which side?

[sidnit33]

The X-position is right on the middle, when turned counterclockwise, moves the signal until the last point to the left, so that shows me it looks like it is working right.

I will be traveling soon, so i will continue cleaning , tightening and testing when i get back after a couple of months, i will post new pictures after i a get any progress, but feel free to continue discussing. i want also to get some gear for testing, like Isolation Transformer and the HV-probe TESTEC HV 250 looks quite interesting, plus some other general gear for my home-lab.

I think in the future I'd like to check some caps also (and kind of doing a restoration if needed) if i am right my osci is from the the year 84' (see picture TB)