I've got a very basic kenwood turntable here. It has a DC motor rated at 12V and a simple power supply.
It came to me non-functional. On investigation the internal fuse was blown. The fuse sits between the transformer and the rectifier (i.e. not on the mains side).
When I replaced the fuse (with the correct value) it initially ran OK. For good measure I decided to replace the smoothing cap as it looked suspect - although I think it was probably glue rather than leaking electrolyte that led me to doubt it... It ran OK for a few minutes before and after capacitor replacement.
I then tried it again and the fuse blew right away.
According to my multimeter the low voltage side of the transformer is providing around 10V AC.
I have checked the diodes (removed from circuit) - they are all OK.
My best guess at this stage is either the motor is bad and drawing too much current, or perhaps the transformer is producing inadequate voltage and similarly causing the motor to draw too much current.
Any thoughts? Inclined to cut my losses at this stage...
It came to me non-functional. On investigation the internal fuse was blown. The fuse sits between the transformer and the rectifier (i.e. not on the mains side).
When I replaced the fuse (with the correct value) it initially ran OK. For good measure I decided to replace the smoothing cap as it looked suspect - although I think it was probably glue rather than leaking electrolyte that led me to doubt it... It ran OK for a few minutes before and after capacitor replacement.
I then tried it again and the fuse blew right away.
According to my multimeter the low voltage side of the transformer is providing around 10V AC.
I have checked the diodes (removed from circuit) - they are all OK.
My best guess at this stage is either the motor is bad and drawing too much current, or perhaps the transformer is producing inadequate voltage and similarly causing the motor to draw too much current.
Any thoughts? Inclined to cut my losses at this stage...
Was the smoothing cap the same value?
Perhaps a switch-on surge blew the fuse, I'd try with a smaller cap as the old one may have had a higher ESR and thus protected the fuse.
I'd also try with the motor disconnected a few times, to isolate the fault.
Same value (1000uF 16v). To clarify: With the old cap in circuit it had already blown the first replacement fuse I tried (& the one it arrived with), but worked OK for a while after a 2nd replacement, and initially still OK after cap replaced.
Did you get the polarity of the replacement capacitor correct? Having it reversed could cause this. On the other hand, something else was likely bad to make the fuse blow the first time.
I suspect the motor. Disconnect the motor and check if the fuse blows. Power the motor with a separate power supply and see if it pulls excessive current. A 12V DC motor would likely use brushes, in which case it would (imho) not have a long life for running a turntable, as the brushes would wear out/short out.
Have had a play as suggested.
With the motor disconnected and a fresh fuse fitted the power supply itself appears functional and has not yet blown a fuse. I measured just over 15V DC at the output, which does seem a little high.
The motor runs fine off a regulated bench supply set to 12V (no load). Typical current draw is 20-30mA (more at 45rpm), this sometimes peaks at switch on, but only to around 100mA.
I was able to get the motor to draw 400mA max but only by artificially creating a physical load by placing my finger on the spindle and slowing it down. I don't think the drive belt is tight enough on the motor spindle for such an extreme load to be exerted in practical use.
I'm perplexed.
With the motor disconnected and a fresh fuse fitted the power supply itself appears functional and has not yet blown a fuse. I measured just over 15V DC at the output, which does seem a little high.
The motor runs fine off a regulated bench supply set to 12V (no load). Typical current draw is 20-30mA (more at 45rpm), this sometimes peaks at switch on, but only to around 100mA.
I was able to get the motor to draw 400mA max but only by artificially creating a physical load by placing my finger on the spindle and slowing it down. I don't think the drive belt is tight enough on the motor spindle for such an extreme load to be exerted in practical use.
I'm perplexed.
DI01 diode connection seems to have come off on one end. Check all the diodes to ensure proper connection and measure the DC.
Take a look at the picture in post #3.
Look closely at the blue mains wire. Looks like there might have been a bad connection from wire to pcb. That black stuff comes from sparks,
and might be conducting. I would cut off the wire, cut off a cm. or so, get fresh copper, and solder it back properly. Maybe
has nothing to do with the error, but it doesn´t look safe 🙂
Look closely at the blue mains wire. Looks like there might have been a bad connection from wire to pcb. That black stuff comes from sparks,
and might be conducting. I would cut off the wire, cut off a cm. or so, get fresh copper, and solder it back properly. Maybe
has nothing to do with the error, but it doesn´t look safe 🙂
🙂 I should have explained that that photo was taken while I was checking diodes. They are now properly soldered in place.
I'm not sure, mains wiring seems sound to be honest and I doubt what you've noted is related to the fault. If I can solve the issue maybe I could inspect more closely but at this stage it's possible the whole thing will end up in the bin.
Hi,
With the motor cable out and no power check the resistance between IC1 pin 4 and 3. A low resistance means bad chip.
With the motor cable out and no power check the resistance between IC1 pin 4 and 3. A low resistance means bad chip.
You say that you can pull 400 ma from the transformer/power supply when you make the motor drag between your fingers. That might lead me to investigate the platter and bearing seeing how this is an older machine, and also I have seen in some cases where the gears/cams are only partly in play, but not actually doing anything. If that were the case, they might be pulling extra current via mechanical 'partial engagement'.
In general how does the speed hold up?
On the motor assembly. I wouldn't have guessed it. It didn't show up on the parts list that I noticed either, it made me wonder.
In general how does the speed hold up?
On the motor assembly. I wouldn't have guessed it. It didn't show up on the parts list that I noticed either, it made me wonder.
Yes, it crossed my mind that a drop of oil on the motor spindle and main bearing might reduce load, but there's nothing to suggest that friction is excessive, and as noted previously the belt is not tight enough anyway to create the sort of drag I imposed with my finger - the belt would just slip if the load from the platter was excessive.
It's an odd one, with the bench psu the motor doesn't draw enough current to take out the fuse, and yet the internal PSU seems perfectly happy without the motor connected. I'm wondering though whether the 15v I measured without the motor connected is too much, and thinking I might try reverting to the original capacitor and measure the no load output again to see whether reduced ESR in the new cap is causing an issue as suggested before. Checked with a resistance meter the original cap seems OK.
Once I've done that I'll do a basic mechanical overhaul and try reconnecting the motor.
Ultimately it might make most sense just to remove or disconnect the internal PSU and fit a DC socket. I've already spent more time on the unit than I should have, and using an external PSU would be a quick and relatively inexpensive solution.