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HP 8561E error 358 - SPAC CAL.

Question asked by canadianulcas on May 30, 2015
Latest reply on Jun 29, 2016 by AgilentHpSpectrum
Hi,
My 8561E spectrum analyser displays "ERR 358 - SPAC CAL". 
The instrument seems to function correctly on all frequencies at spans below 2MHz. At spans of 2.01MHz and up, the ramp generator becomes instable and the sweep time seems to default to about 50ms or so, and stays that way for any other chosen sweep interval. Using the Service manual and the CLIP documentation, I think I have traced back the problem to the HSCAN signal (on A3 - interface board) that controls the ramp generator. The HSCAN Latch (U615A on the A3 board) receives the correct 1MHz clock from U616 and the correct SCANLTCH_RES signal from U611 for spans of 2MHz and below, and the ramp generated is a nice and stable 0 to 10V, locked to the HSCAN signal. When I increase the span to 2.01MHz, the ramp keeps the same slope but it becomes shorter, about 0 to 5.1V only, but is still locked to the HSCAN signal and both are jumping left and right on my scope and are intermittent. Going back to 2MHz span, brings everything under control and working fine. It looks that either the trigger signal for HSCAN is unstable (but the trigger circuit seems to work ok) or the SCANLTCH_RES signal coming from U611 is sent to early precluding the ramp to complete it's full excursion. There is another signal HSWP generated, I think, by Q601 from the HSCAN, but I don't know where it is going and for what purpose. I don't know how to check where is the SCANLTCH_RES signal coming to the U611 IC and if it's timing is correct.
I have also checked the HBKT_PULSE coming from A2 - controller board, and it seems to follow the behaviour of HSCAN, stable for 2MHz span and jumpy in 2.01MHz and upper spans.
Does anybody have an idea what is the cause of this behaviour?

Thanks

Edited by: Canadianulcas on May 30, 2015 2:52 PM  

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