Turn-table Tonearm Motor Drive controller - Page 1
Forum section: electronics / projects

author: NivagSwerdna
author_rank: Super Contributor
timestamp: January 16, 2017, 03:30:23 pm
content: Just when I thought I had time to look at some of my project backlog my old record turntable seems to have died...The turntable, Technics SL-QD33, has a small 5V motor which operates a worm gear to advance/retract the tone arm. The motor works in both directors.I believe the part that is causing the problem is IC502 which is SVIBA6218, a part which is made from unobtainium.SVIBA6218 is a 9-pin device (arranged in a single line of pins)Pins 2,5 & 8 are GND, Pin 6 is 5V supply (connected to a 1A regulator). The motor goes between Pins 7 and 9. Pin 4 is NC.Pin 1 and Pin 3 are the drive control where the combinations are...H H = BrakedL L = FreeL H = ForwardH L = ReverseI measured the signals going into the current device and it seems to be driving around 3V7 for a 'High'So... I'm looking for a very simple replacement H-bridge that can drive a 5V 1A motor that follows the above truth table. The motor only runs for a few seconds every record play to position the needle and then retract it at the end.Devices like L298N seem to have a separate enable which would require me to have extra logic (i.e. an OR) and it is dual which seems a bit un-necessary.Any suggestions for a drop-in replacement?Thanks in advance

author: CJay
author_rank: Super Contributor
timestamp: January 16, 2017, 04:08:00 pm
content: L9110S to replace your Rohm BA6218 perhaps?Ratings are similar but you'd need to check the datasheet for logic compatibility.Available on modules from China for 99p.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: January 16, 2017, 04:14:33 pm
content: Quote from: CJay on January 16, 2017, 04:08:00 pmPossibly but not sure H H gives you 'brake'I came across DRV8837 although the form factor isn't the most friendly...

author: retrolefty
author_rank: Super Contributor
timestamp: January 16, 2017, 04:26:08 pm
content: Quote from: NivagSwerdna on January 16, 2017, 04:14:33 pmI would think that giving up the brake function wouldn't hurt too much.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: January 16, 2017, 04:38:38 pm
content: I can hardly believe this...http://www.ebay.com/itm/ROHM-BA6218-2-PCS-/321911811699Once you told me that it was Rohm I found a listing... Not sure they are real or not but looks hopeful.Re: Brake.... I think you are probably correct. The motor drives a worm gear, it will probably not want to move much.

author: CJay
author_rank: Super Contributor
timestamp: January 16, 2017, 05:00:13 pm
content: Looks like it could be a goer but I'd take a few minutes and clean/re-lube the worm and associated gubbins.It'd also be worth checking the current drawn by the motor once you've done that, used to be a common fault when motors wore out that they'd just not start. Hooking them up to a power supply to 'test' them wasn't useful as when there was extra current available they'd start right up.If you want to try one of those L9110 boards, I've got a couple sat here and could pop one in the post.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: January 16, 2017, 10:37:41 pm
content: Quote from: CJay on January 16, 2017, 05:00:13 pmFair point. I think I had a very modest current limit when I tested and it looked reasonable but I didn't operate when attached to the full mechanical set-up so that is a definite possibility.Quote from: CJay on January 16, 2017, 05:00:13 pmVery kind but I think I'll just park the project and await the part I ordered on EBAY. I do sort of agree/worry that I might not be looking at root cause yet. But fingers crossed.

author: amyk
author_rank: Super Contributor
timestamp: January 17, 2017, 04:04:37 am
content: BA6218 is old, but looks like they're still available:http://www.alltronics.com/cgi-bin/item/BA6218/63/BA6218-Motor-Driverhttp://www.digikey.com/product-detail/en/rohm-semiconductor/BA6218/BA6218-ND/658357

author: NivagSwerdna
author_rank: Super Contributor
timestamp: February 19, 2017, 09:22:06 pm
content: Fitted and fixed my Technics SL-33QD turntable today.To be honest I'm not 100% sure this was the issue, could still be the motor being weak running in one direction, but it does appear to be working for now (after a bit of recalibration).Thanks EEVBloggers