Thanks RCruz, Frans, Bksabath ... now I know I should have deferred that Reichelt order ;-/
Next Question:
Right after lunch (never do something on a full stomach
) I "tested" my diode strings.
(almost everything OK but) On one board L201-209 would not lite...
So I checked the 1st 4 only... with the PS still on 20V...
...even the lowest current setting on the PS did not rescue me ...
Now I need 4 additional green LEDs ... and I don't want them to look different (no, no, no).
What brand and type are the green LEDs from the GB ?
Thanks
Next Question:
Right after lunch (never do something on a full stomach
) I "tested" my diode strings. (almost everything OK but) On one board L201-209 would not lite...
So I checked the 1st 4 only... with the PS still on 20V...
...even the lowest current setting on the PS did not rescue me ...
Now I need 4 additional green LEDs ... and I don't want them to look different (no, no, no).
What brand and type are the green LEDs from the GB ?
Thanks
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None of the simple advice relating to my oscillation problem worked. So far i have been trying to not completely ruin the boards and have avoided haphazardly replacing components.
But is seems some more decisive action is now required. Judging by the number of successful builds it simply has to be related to a component, either out of spec, or in some way mismatched to the circuit.
So, in order to narrow this down a bit i've been thinking: there are a whole lot of transistors, not even sure why so many, which only seem to deal with dc op points of the input devices and the servo signal. Would it be possible to remove Q11 and Q5 and supply the input devices emitter resistors via resistors from the related PS lines?
This should eliminate 16 semiconductors from the "suspicious" list, right?
Or is this just silly - it's a dc signal after all.
If there are no objections to this, as a next step i am thinking of removing the parallel devices and leaving just one input pair.
But is seems some more decisive action is now required. Judging by the number of successful builds it simply has to be related to a component, either out of spec, or in some way mismatched to the circuit.
So, in order to narrow this down a bit i've been thinking: there are a whole lot of transistors, not even sure why so many, which only seem to deal with dc op points of the input devices and the servo signal. Would it be possible to remove Q11 and Q5 and supply the input devices emitter resistors via resistors from the related PS lines?
This should eliminate 16 semiconductors from the "suspicious" list, right?
Or is this just silly - it's a dc signal after all.
If there are no objections to this, as a next step i am thinking of removing the parallel devices and leaving just one input pair.
Not sure why you mention this Joachim. There are no dc issues on the board at all. All input devices work at a very similar 3.4mA...
My idea was to remove the "unnecessary" part of the circuit in order to simplify it for troubleshooting the oscillation issue. Any suggestions about that? Alternatively i could build it afresh on a proto-board, get parts which work and then move them to the PCBs. Just seems like extra work and potentially different layout.
My idea was to remove the "unnecessary" part of the circuit in order to simplify it for troubleshooting the oscillation issue. Any suggestions about that? Alternatively i could build it afresh on a proto-board, get parts which work and then move them to the PCBs. Just seems like extra work and potentially different layout.
Not really. It's a 60MHz scope with sync issues. DC rails are entirely noise free.
Ok. As this will involve desoldering them from the board do you think i should just leave one pair while experimenting?
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Yes, this is the main issue. The apparent dc wandering is probably also a result of the oscillation.
Later tonight i will try taking out the helper transistors and if this doesn't help will also try the base stoppers. I guess these were not in designed in because of the additional noise.
Didn't do any of this. The time spent on this project simply hit a stop loss and it's being shelved.
It is very seldom that i build analogue projects on pcbs. It is usually dead bug style or multilevel protoboards. Temptation to follow an easy route took over this time but for some reason did not work for me. If i get free i will probably prototype the whole thing and find parts which will work together. And maybe leave it on a proto board. The entire ground plane concept for an analogue circuit is not much to my liking anyway.
Many thanks to Joachim and Hesener for their time and helpful suggestions.
Hi analog_sa, don't give up so quickly! This is a high performance circuit, and it might just be a couple small things that spoil the fun.....
ground planes have been used in analog for some time, much longer time for RF actually. If done well, they are very helpful to circuit performance. Personally I don't think its the ground plane that is at fault here. PM sent.....
ground planes have been used in analog for some time, much longer time for RF actually. If done well, they are very helpful to circuit performance. Personally I don't think its the ground plane that is at fault here. PM sent.....