Author Topic: X-Pos on Hameg HM5014-2 Spectrum Analyser  (Read 606 times)

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Offline Rod___

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X-Pos on Hameg HM5014-2 Spectrum Analyser
« on: January 27, 2019, 12:25:56 pm »
Hi,

I have a Hameg HM 5014-2 SPectrm Analyser. The unit works fine but the beam position in the X-axis is off by about 2mm. i.e. the Centre frequency is 2mm to the left of the centre graticule line. This is also seen when viewing the centre line of the trace-rotate pattern. Of course this doesn’t make the unit inaccurate in any way but it is annoying.

I have the service manual but the only trimmer I can find relating to ‘X’ is the X-Gain. There are also trimmers for Astig and Intensity. These are all on the XYZ Board (Page 50 of the service manual).

X-Pos is mentioned on page 48 but that is just a fixed potential divider in the X-Final Amp. nothing appears to be adjustable. Please see attached.

Any help in pointing me in the right direction would be really appreciated.

Best Regards
Rod
 

Offline TurboTom

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Re: X-Pos on Hameg HM5014-2 Spectrum Analyser
« Reply #1 on: January 27, 2019, 11:55:33 pm »
It's on the digital control board, see attachments.

Cheers,
Thomas


P.S. C21 at the output of the buffer opamp is REALLY awkward, seems like someome didn't know what he's doing there. This designer must have been lucky that it worked like that anyway...
« Last Edit: January 28, 2019, 03:31:21 pm by TurboTom »
 
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Offline Rod___

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Re: X-Pos on Hameg HM5014-2 Spectrum Analyser
« Reply #2 on: January 28, 2019, 04:10:12 pm »
Hi Thomas,

Many many thanks, the beam is now centred.

Do you happen to know if P1, to the left of P2 on the main board schematic (page 38) is the trimmer for the marker position. If I can get that to be reading the centre frequency when it is on the centre frequency then everything will be correct.

Thanks again.
Rod

P.S. to your P.S. I'm still very much a learner, I can't see the problem with C21. I assume it just takes any parasitic oscillations to ground leaving the op-amp to funtion correctly as a follower before the next stage. The op-amp is only dealing with DC input. But I'm probably completly wrong :-//
« Last Edit: January 28, 2019, 04:53:17 pm by Rod___ »
 

Offline TurboTom

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Re: X-Pos on Hameg HM5014-2 Spectrum Analyser
« Reply #3 on: January 28, 2019, 04:47:40 pm »
Rod -
This P1 thing rather looks like an X slew rate adjustment to me. Apparently, the X/Y amplifiers consist of a quite interestingly designed resistive A/D converter each and a discrete sample/hold ciruit, followed by a switchable slew-rate amplifier (integrator to be able to display lines and not only dots...). But that's my understanding of the circuitry without going further into detail. Since both the X position of the SA trace and the positions of the cursors are generated by the computer section, it shouldn't be necessary to separately calibrate the cursor position. These half-analog half-digital designs of the '90s can be bitches to troubleshoot. But then again, with the (usually available) schematics and some brain exercise, at least in most cases that's possible while more modern, fully digital systems are mostly just "black boxes"...
Good luck and all the best,
Thomas
« Last Edit: January 28, 2019, 04:51:29 pm by TurboTom »
 


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