Quote:
Originally Posted by Alistair D
I have 3xV4s here. These are my results for the D604 readings.
V4/1 V4/2 V4/3
0 mins 10.473 10.429 10.430
5 mins 10.657 10.581 10.589
10 mins 10.678 10.600 10.612
On all 3 units the voltage rose quite rapidly during the first 30 seconds or so.
Regarding the other measurements you want, can you give me the exact circuit references just to be sure I am measuring the exact point you require. I assume that these readings are to be taken after 10 minutes.
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Hello Al,
thank you for the measurements. As I can see from your measurement values, you measured the voltage across the diode instead of the voltage to ground. I just did the same on my unit and got the following values:
10.32V 0 min
10.57V 1 min
10.63V 3 min
10.646V 5 min
10.648V 10 min
This looks a lot like the diodes in your V4s, so I think, its normal.
Regarding the additional measurements, I will prepare a marked circuit diagram and a PC152 photo for you later, if I run out of other debugging options. I do not want to steal more of your valuable time than necessary.
Quote:
Originally Posted by Argus25
With regards to the 10V zener, it is expected to have a positive tempco, meaning the voltage across the diode will increase with heating. That could be expected to slightly alter the balance but most of the drift on that power rail should be largely ignored , but it could be worth trying a new one and as suggested adding a series diode to help cancel some of that drift.
It looks to me though that the designers were struggling with temperature drifts which is why they added the thermistors in x5 mode. Also as I recall those dual fets do run warm. Looking at the board layout, there is a different physical spacing between the thermistors and the dual fets for the two channels. Try bending the CH2 thermistor (TH602) away from the body of the fet(TR607) so the the physical spacing of it from the fet is more like the channel 1 situation.
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Hello Argus25,
thank you for your expertise regarding the 10V zener. I did not expect the drift at this point to be kind of unimportant. Your analysis of the role of the thermistors sounds very interesting. I just did what you suggested with TH602 and the result was a much more consistent convergence of the CH2 drift. It now settles after about 5 minutes. However, it still has a kind of inconsistent convergence point which I attribute to the highly wiggle sensitive CH2 vertical position potentiometer. CH1 is perfectly usable after only 1 minute of warm-up and does not have any wiggle problems at the corresponding potentiometer.
Since the initial deviations from previously optimized vertical positions on cold startup of CH2 are 5 times more off than for CH1, I still have to find the component causing this. I have also the impression, that CH2 reacts more sensitive to the potentiometer than CH1. Maybe I should also try a second cleanup of the double vertical position potentiometer of CH2, although I already did that very thoroughly on both double potentiometers.
Denis