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General Category => General Discussion => Topic started by: Mrs R on October 01, 2011, 20:11:37 PM

Title: HITEC HV SERVOS ie 7950th
Post by: Mrs R on October 01, 2011, 20:11:37 PM
Hi! Guys.
Has any one here done any work with HITEC's 7950TH servo.
My main problem is A/C noise on the regulated power line.
It has an Inductor Joining V+ to V- then a 22uf Tantalum Cap. to the V in on the cmos regulator and a 1uF Tant. Cap. on Vout. Vout is 3.1 volts at 200ma.
I am changing the 22uf Cap to 47uF and the 1uF to 2.2Uf with .01 uF on the in tags and out Tags to Ground on the Regulator and fitting a 10 uH choke on the Vout line.
Any suggestions that may help stop the A/C noise.Voltage cane't go below 3volts so I can't put an RC filter in
the amps can be reduced as it's at maximum that the ATMEG48 Microcontroler can take. I was thinking of putting a .01uF Ceramic and 5ohm Resistor at the input pin on the MC but can't see that that would effect the A/C noise. ANY HELP would be appreciated
THANKS GUYS Denise
Title: Re: HITEC HV SERVOS ie 7950th
Post by: _pike on October 01, 2011, 21:06:19 PM
Hello and welcome to the forum.I haven't used the particular servo but i would like to tell me what kind of problem creates you the noise.Also ( i think maybe wrong) inductors in power supplies are usually connected in series and not in paraller.So what can you do?Try to replace the inductor with 2 VK200 in series also what type are the diodes and what kind of regulator are you using?
Title: Re: HITEC HV SERVOS ie 7950th
Post by: Mrs R on October 02, 2011, 22:28:31 PM
_Pike,
It's a cmos Reg. but HITEC won't supply the make and specs. I have pulled the birdnest apart and drawn the Schematic.
The A/c noise is leakage from the signal line, the problem is that if I stop the noise at the mosfet that feeds to the Analog
(ADC) line I can't reprogram the servo.It effects pin pbc7 an look at the thats the outlet so you can look at the digital signal with the Scope.
I have searched every where for the make of the Reg. Has a part number on body 9XZ7 if I could find the make I would replace it with a Texas Inst. Reg. I have used some of theirs and they have been very quite. (Note all the components are SMD's) most of the passive are o603 packages. ? What are VK200'ds
REGARDS
Denise
PS the circuit is a nightmare not like the 5955 series which are very nice and easy to fix or mod. Why they put a Inductor in Parallel beats me. but there are things like that all through the circuit.