Technics SL-D3 Direct Drive Vintage Turntable

[Billy R aka DynaFreak]

My faithful Technics turntable I bought in 1979 finally stopped working properly. All functions work ok except the speed controller (it has the little strobe light thing). The speed will change when you adjust the speed control, but it does not maintain the correct speed. Any suggestions on where to start troubleshooting the control circuit?

[Techknowman]

When I was younger, I was a technics certified repairman.
On that type unit there was a driver IC that would go bad in one of two ways.
1 it just stopped working
2 it wouldnt regulate speed correct.
The IC was about 1" wide 1.5" long about 1/4" thick with leads formed into a DIP configuration. I don't recall the part number. I'll dig and see if i can find a schematic.

[Billy R aka DynaFreak]

thanks for the fast reply! I was able to find a service manual at vinylengine.com. The IC is an AN630U 24 pin DIP. and appears to be still available for about 15 bucks.

[Techknowman]

I was just getting the service manual from them as well.
Before throwing the baby out with the bath water make sure the current IC is soldered in well.
At that age the solder could have cracked out around the pins of the ic and that would cause issue.

Also the service manual wouldnt show it but see if there is a "A" or later rev of that IC.
It seems to come to mind that the original AN chip was prone to failure and a newer IC was made to replace it
Never mind the original was AN630, AN630U is the current

[km6xz]

The servo electronics is pretty self contained in the AN630 but a few things can cause speed changes independent of the servo controller IC. Does the speed remain steady when the speed control is off? If it is, than check the control voltage on pin 24 for a steady 17vdc. The speed control pot and speed trimmers will create erratic control voltage if oxidized. Also you can check pin 18 for a steady sine wave clock of 50khz. If it isn't, the chip is probably the problem but in most cases the servo does not work at all if the IC is faulty. Too much does work to be fully confident in the IC being the cause however.
The part by MATSUSHITA is discontinued so any stock you find, you might consider grabbing a couple for future use if needed.

[Billy R aka DynaFreak]

Thanks guys! After putting the turntable back together, now it is operating ok and holding a steady speed. I suspect the pitch adjustment control may have been dirty. I'll will save all your advice in a file for future reference if I have problems again.

[km6xz]

If you and I were right about an oxidized speed control pot, it will occur again unless de-oxidized. An erratic voltage on pin 24 when moving the pot would be the indicator. A light application of D5 DeOxit and exercising the pot would take care it in most cases.