Electronics > Repair

INSTEK spectrum analyzer GSP-827 -6 dBm down than the real value

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G0HZU:
I had a quick skim of the features/modes in an online doc and this analyser can operate as 75R and also 50R.

For example, I think you are meant to calibrate this analyser in 75R mode with an external 75 to 50R attenuator inline? The manual calls it the 'ZZ adaptor'. This zz adaptor will have a loss of just under 6dB. If you calibrate in 75R mode and forget to fit the (ZZ adaptor) 5.9dB matching attenuator during the calibration then you could end up with an analyser that appears to be deaf by about 6dB after calibration.


G4JMO:
Thanks for all the comments. It is some kind of hardware fault, not a 75 /50 mismatch or anything like that. It's behaving in a similar way with external input. I've also found out that the previous owner of my unit had to return it for repair on several occasions for this very fault. Hopefully when its skin is removed, it should be straightforward to find the problem !
Regards

KJDS:

--- Quote from: Adal on March 11, 2015, 10:56:18 pm ---Yes. The -6dBm error are flat across the frequency range

--- End quote ---

Then it is very unlikely that the problem is before the first mixer.

Adal:
Thanks to all for your comments.

Andrew, I agree with your diagnostic. In fact yesterday when I turned my GSP-827, the internal 100 MHz -30 dBm calibration signal appears -34 dBm, only -4 dBm  lower  :-//     
And another fault, when I put an 100 MHz AM -30 dBm signal with 100 % modulation, I canĀ“t resolve clearly the two side band, only the carrier.  :-- 
I make a video in order to show us the test

My strategic for fix it will be
Check the receive path.
Check the IF train and the digitizer.  I hear you suggestion.
 

 

videobruce:

--- Quote from: Aurora on March 11, 2015, 07:54:38 pm ---Sadly GW INSTEK service manuals are as rare as hens teeth. I have been in touch with the support team previously and they will not release service information to the public
Aurora

--- End quote ---
The Chinese are tight lipped. I guess they are paranoid about the competition coping their design. Rigol is the same way. I tried more than once to get a real SM, but there isn't any (so I'm told). Both have something they call a "Service Manual", but all it is is a "verification' manual. The 827 is a older SA, there maybe a possibility doing a search to stumble across something outside of Instek.  ;)

Funny, with the real US companies, most had/have SM's available. Actually with both importers, you have to the equipment serviced in China.

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