Need help with power supply: Diatone DP-EC! turntable.

[rayma]

The pi8c there shows a mounting panel for these in the bottom right corner.
I suppose I could fashion something to secure them.

Insulated, hopefully.

 

[rayma]

I get the impression someone else has been in and around the power side of things.

A short there could damage other parts in the power supply, so check the two higher voltage supplies carefully.
The lowest voltage supply seems ok (purely by accident).

 

[cal16v]

Again, while it's shoddy the legs were insulated with plastic sleeves at least.

Ok some voltages (if I've done this right)!

1 - 0.9V
2 - 0.44V
3 - 0.00V

Hopefully this is what you might have anticipated.

Thank you for the warning. I will be I can assure you.

cheers

 

[rayma]

Check the voltages again as in post #4. Maybe you'll luck out.

 

[cal16v]

Check the voltages again as in post #4. Maybe you'll luck out.

So the following is a repeat measurement as in post 4;

#17 - 2.7 - 3VDC
#23 - 9.3mVDC
#27 - 5.86VDC

Would it be better to halt at this point and I spend some time re-soldering, replacing wiring that looks shoddy etc. Could I change these transistors entirely including wiring?

Would that be a more sensible approach?

 

[rayma]

Could I change these transistors entirely including wiring?

There is likely to be more damage than just the pass transistors. You'll have to check both bad supplies carefully,
especially the Zener diodes and the on-board transistors they feed.

 

[cal16v]

Do you get any DC voltage on C313/R305?

I suspect you might have a short on the +12V somewhere that's pulling everything down.

If it's not too much hassle, try disconnecting the RED wire at #23 and measuring again. You can also try measuring resistance to ground at this spot before/after (with power off).

BTW, the solder joints on the transformer primary look a bit crusty to me, the 0 V in particular. That clearly wouldn't be helping matters. Any change of output voltage if you wiggle the cable? A bit of flux and fresh solder may be appreciated.

Is the power switch delivering a decent enough contact resistance?

A flaky primary connection or power switch are about the only reasons I can think of for why unloaded voltages were higher than loaded. Well, either those or a flaky thermal fuse... At times these have been known to go bad all by themselves, but here the potential short on +12V might just have sort of degraded it. Maybe try getting a resistance reading on the primary and observing whether tapping the xfmr changes anything.

Worst case would be some shorted turns. That would make the transformer get quite warm though.

Thank you for posting.

Results

Voltage @ leg of R305 is -4.6VDC.

Resistance @ #23 (red wire connected) - 2.9k ohms / (red wire disconnected) - !7.5M ohms, power off.

Voltages (as per post 4) with red wire @ #23 disconnected;

#17 - 1.4VDC
#23 - 74.5mVDC
#27 - 5.7VDC

I will spend some time as you say tidying up various solder joints and wires.

Thank you.

 

[cal16v]

So to eliminate a likely dodgy transformer from the equation I need supply the 3 x secondary voltages from an external box x 3 transformers correct?

It looks as though I could tap into the TT switch to turn on the transformer box whenever the arm is moved? If so then I presume i would need to maintain a safety earth on the TT correct?

Otherwise and again if I'm reading correctly the old transformer and its 240V feed wire can be removed. The power cord can then become a L,N feed to the switch wiring directly, and a safety ground is last but not least wire in the cable.

I have managed to find and order replacement pass transistors as well.

Thoughts, advice...

 

[Kay Pirinha]

To examine the PT, disconnect the transformer's three secondary windings from the power supply board and measure the three AC voltages. What do you read?
Luckily all three DC supplies refer to common ground. So if the PT should be burned, it could be replaced by a simple 15-0-15 Vac one of suitable power capability, preferably a toroid.
Best regards!