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Old 13th November 2017, 09:41 PM   #401
BlacK_Chicken is offline BlacK_Chicken  Germany
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Ok, after having a glance at the AD536 datasheet I suspect this beeing a settling time issue. If settling time is higher than expected, the output voltage lags behind and the PIC ranges down.

Attached a scope-screenshot of PIN1@AD536 (blue) and PIN24@PIC (red). Input signal 1Vrms/1.2kHz. One can clearly see, at which thresholds the PIC chooses to range up or down. Are the treshold-values ok?

The postfilter: C16 is populated, C13 is not. ok?
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File Type: jpg 20171113_debug_001.jpg (358.1 KB, 292 views)
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Old 14th November 2017, 06:26 AM   #402
jan.didden is offline jan.didden  Europe
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B_C, just for my understanding, it is only with say 1V input? If you turn up or turn down the input level, does it 'move through' the cycling going to a higher or lower att setting?
If you can move through it, it points to a specific resitor or relay, if not it points to a system issue.

Your last comment about probing the AD536 point to a possible issue with C16 or C20, see attached. Can you verify correct connection, to exclude a PCB trace break somewhere?

Edit: didn't see your last post until now. We had the same thought ;-)

Jan
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File Type: png Capture.PNG (33.2 KB, 284 views)
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Last edited by jan.didden; 14th November 2017 at 06:31 AM.
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Old 14th November 2017, 06:58 PM   #403
BlacK_Chicken is offline BlacK_Chicken  Germany
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Quote:
Originally Posted by jan.didden View Post
B_C, just for my understanding, it is only with say 1V input? If you turn up or turn down the input level, does it 'move through' the cycling going to a higher or lower att setting?
If you can move through it, it points to a specific resitor or relay, if not it points to a system issue.
Actually it is most recognisable and asolutely reproducable at 1,0 Vrms but it happens at all fast transient input level changes -> as long, as I turn the level knob of my generator fast enough it loops at almost any level.

This again points me to the settling time issue. Thanks for the schematic, I'll double check tonight.
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Old 14th November 2017, 07:21 PM   #404
BlacK_Chicken is offline BlacK_Chicken  Germany
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Originally Posted by BlacK_Chicken View Post
Thanks for the schematic, I'll double check tonight.
Seems ok. I could exchange C16 and C20 with new caps, but I am not sure if this really helps since a wrong part-value is very unlikely.
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Old 14th November 2017, 07:50 PM   #405
jan.didden is offline jan.didden  Europe
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How large are the excursions? Only + and - 4dB or are they different depending on where, levelwise, it happens?

Jan
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Old 14th November 2017, 08:06 PM   #406
BlacK_Chicken is offline BlacK_Chicken  Germany
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Yes, they are differently.

For instance. Just now I turned the AR on with 0,4634Vrms/1,227kHz at the input and it cycles infinitely between +12dB and 0dB.

Turning up to 1.53Vrms it cycles between -8dB and 0dB.

Another turn on the level knob of my generator gives 2.40Vrms and the AR is still cycling between -12dB and -4dB.
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Old 14th November 2017, 11:13 PM   #407
soongsc is offline soongsc  Taiwan
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Originally Posted by BlacK_Chicken View Post
Yes, they are differently.

For instance. Just now I turned the AR on with 0,4634Vrms/1,227kHz at the input and it cycles infinitely between +12dB and 0dB.

Turning up to 1.53Vrms it cycles between -8dB and 0dB.

Another turn on the level knob of my generator gives 2.40Vrms and the AR is still cycling between -12dB and -4dB.
Does it finally settle to the correct setting?
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Old 15th November 2017, 07:24 AM   #408
jan.didden is offline jan.didden  Europe
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B_C,

The only thing I can think of right now is that the averaging cap is not connected at one side.
If you exclude that, I propose you send me the atten board and I check it out here and fix as required. Free of charge of course. Otherwisw we could at this a this Christmas ;-)

Let me know if the cap fixes it, if not I send you my shipping address via PM.

Jan
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Old 15th November 2017, 07:26 AM   #409
jan.didden is offline jan.didden  Europe
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Some people have asked for the control codes so they can use the settings info externally. Here they are; I will also post them at the website.

You can simply use a longer flatcable that extends outward and tap off the relevant pins.

Jan
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File Type: pdf AR atten code.pdf (20.9 KB, 31 views)
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Old 15th November 2017, 06:28 PM   #410
BlacK_Chicken is offline BlacK_Chicken  Germany
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Originally Posted by jan.didden View Post
B_C,

The only thing I can think of right now is that the averaging cap is not connected at one side.
If you exclude that, I propose you send me the atten board and I check it out here and fix as required. Free of charge of course. Otherwisw we could at this a this Christmas ;-)

Let me know if the cap fixes it, if not I send you my shipping address via PM.

Jan

Thanks a lot for the offer. I hope this is not necessary. I am pretty sure now, it must be either the Average-Cap or the Post-Filter. I have some 0805/1206 caps here to test and while the unit is dis-assembled I can double-check the connections of C16 and C20.
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