How to make VCR drum motor work with controler IC? - Page 1
Forum section: electronics / projects

author: mondalaci
author_rank: Contributor
timestamp: January 25, 2014, 01:44:15 am
content: Hi guys,Recently, Idisassembled our old VCRand extractedits drum motoralong with its controller board and IC. The IC goes by the name ofKA8328Dand despite the datasheet I'm such a world-class noob that I cannot make it work.This is the pinout of the 2x3 diagonal header that is featured on the board:wireGNDVCCVCTLwirehallThere's a circular track around the drum going back and forth in zigzagged fashion. Its two ends are the wire pins. The other pins are featured in the datasheet.I provided 8 volts (which according to my understanding is the minimum supply voltage) through VCC and GND but the motor didn't start spinning. Also wired VCC to VCTLhoping that it'll do the trick but didn't work either.Some questions:What should I do to make this sucker spin? How should I control its speed? How could I operate this motor at its maximum possible speed? (I'm thinking about using it for a POV display eventually.)Thanks in advance!

author: amyk
author_rank: Super Contributor
timestamp: January 25, 2014, 10:31:47 am
content: Making it run has to do with the Ictl and Vctl pins, which take a very small control voltage (~2V according to the datasheet) to control the motor current; by putting Vcc into it you may have fried that part...

author: mondalaci
author_rank: Contributor
timestamp: January 25, 2014, 11:21:27 am
content: Where is this 2V stated exactly? (So far I thought that the "Operating supply voltage" is the relevant value which is 8-16V.)May I have fired the IC or the motor?What's the purpose of VCC then?Thanks!

author: sleemanj
author_rank: Super Contributor
timestamp: January 25, 2014, 11:39:40 am
content: Graph page 5 & 6 indicate that VCtl range is 2.3 to 5v.

author: mondalaci
author_rank: Contributor
timestamp: January 25, 2014, 12:00:59 pm
content: Thanks for the answer!Anyone seeing this thread is welcome to answer the rest of my questions because I'm still clueless about those.

author: rexxar
author_rank: Frequent Contributor
timestamp: January 25, 2014, 06:47:00 pm
content: Quote from: mondalaci on January 25, 2014, 11:21:27 amOperating voltage, or Vcc is what actually powers the chip, and probably supplies power for the motor.Vctl is acontrolsignal. It is usually far less than Vcc, and if you put 8V up it, you're likely to burn out the IC.The Vctl signal is what tells the chip to actually turn the motor on. I just skimmed the datasheet, but it looks like as Vctl should be 2.5V, and the motor speed is set by an internal resistor, and is not variable. Remember, this is designed for a VCR, where it's very important that the speed of the drum is constant. Look at page 10 of the datasheet.If you were adventurous, you could design your own driver, but I'll hazard a guess that that's a bit out of your scope right now.Even though the speed is preset, it's still pretty fast, it should be something like 1800 RPM. You should try giving it 9 or 10 volts to Vcc, and 2-2.5 volts to Vctl and see if it spins up. Be sure you've got a good supply for Vcc, because it's going to want to pull an amp or more.

author: mondalaci
author_rank: Contributor
timestamp: January 25, 2014, 07:18:10 pm
content: Thank you so much for elaborating on that, rexxar! I'm gonna give it a spin (pun clearly intended).

author: N2IXK
author_rank: Frequent Contributor
timestamp: January 25, 2014, 08:30:47 pm
content: The zigzag track on the board is a pickup coil used for generating a servo signal needed to synchronize the head drum rotation to the sync pulses from the video signal during record, and switch from one video head to another during the vertical blanking interval during playback. You don't need to worry about it if all you want to do is make the motor spin up.The hall sensors and related circuitry should already be on the board. All you need should be power on the Vcc pins (+12V) and control signals into Ictl and Vctl, and the motor should spin.The application circuit on p13 of the datasheet should be pretty close to what you have on your board.

author: mondalaci
author_rank: Contributor
timestamp: January 25, 2014, 10:09:42 pm
content: Thanks for the additional info, N2IXK. Shouldn't the minimum 8V be sufficient? Hopefully I didn't fry the IC.

author: N2IXK
author_rank: Frequent Contributor
timestamp: January 25, 2014, 11:50:52 pm
content: The chip should work on 8V, but 12V would be the typical supply voltage in the VCR. The datasheet shows typical characteristics measured at Vcc of 14V.