Constant speed motor teardown - Page 1
Forum section: electronics / projects

author: Zero999
author_rank: Super Contributor
timestamp: July 07, 2022, 09:37:25 pm
content: I thought I'd crack open one of those constant speed motors found in old turntables and cassette players, which wasn't working.It turns out the motor itself worked, but the speed controller board was broken. The PCB was fractured straight down the middle and a small piece missing. Interestingly it's a ceramic PCB, with the resistors directly deposited onto it, along with the potentiometer track. Has anyone seen anything like this before?I suppose using a ceramic makes sense because the chip on board gets quite hot and the board needs to act as a heatsink. I imagine depositing the carbon film resistors directly on the board is just cheaper than soldering them on separately. It might also help with the power dissipation, but I don't believe the dissipate more heat.Anyway, it's interesting, but the motor is probably not worth repairing. I just thought I'd post this because some people might find it interesting.

author: Benta
author_rank: Super Contributor
timestamp: July 07, 2022, 10:12:38 pm
content: Never seen one like it before.Is it a belt-drive or direct-drive turntable?

author: Zero999
author_rank: Super Contributor
timestamp: July 08, 2022, 09:29:51 am
content: Quote from: Benta on July 07, 2022, 10:12:38 pmI don't remember. I must've taken it out of an old piece of equipment and put it to one side, with the intention of looking at it later, but forgot about it. It might have even been a CD player. I've seen similar motors inside those before.I wonder if it's possible to decapsulate that COB IC? It would be interesting to see what's under that black blob.

author: Berni
author_rank: Super Contributor
timestamp: July 08, 2022, 10:19:24 am
content: Pretty advanced construction indeed. Id expect a regular PCB in there.I suppose this is what you get when you go into the really huge volumes of mass production where the cost of individual resistors becomes significant.Some of the black goop becomes brittle when at soldering temperatures, so you can chip away at it in small pieces. Otherwise it is done using hot nitric acid as it eats away the polymeric crap while leaving the silicon die and bond wires intact. But that stuff also loves to eat flesh and a lot of other things. Tho it is possible that a strong solvent like acetone might eat away at it or soften it if you leave it submerged for a while.

author: strawberry
author_rank: Super Contributor
timestamp: July 08, 2022, 04:05:10 pm
content: Quote from: Benta on July 07, 2022, 10:12:38 pmsingle speed turntable and even without quartz PLL.green check mark maybe SONY or Samsung did ??

author: Haenk
author_rank: Super Contributor
timestamp: July 08, 2022, 04:23:33 pm
content: Quote from: strawberry on July 08, 2022, 04:05:10 pmI'd say "not Samsung", as there is a Chemicon cap used. Samsung would have probably used a Sanyo cap.

author: Zero999
author_rank: Super Contributor
timestamp: July 08, 2022, 09:18:26 pm
content: I don't know the brand. I'm afraid I can't find the outer case either. I took this motor apart awhile ago.