Denon DP-52F Running Crazy Hot!

[sevi]

Hello,

The heatsink next to my Denon DP-52F's motor is getting very hot. So hot that it triggered the thermal fuse inside the motor.

I did remove the thermal fuse and recapped the motor board. It is running now, speed is stable, but the heatsink with the two Sanken 2sc2023 on it (see photo attached) still gets way too hot.

What could cause this?

Any ideas/input would be highly appreciated.

Cheers,

sev

 

[curtisw99]

When a transistor shorts , it gets hot.
Check them using diode mode on a multimeter

 

[sevi]

Let me check.

 

[sevi]

When a transistor shorts , it gets hot.
Check them using diode mode on a multimeter

Hello curtisw99, thank you for your answer!

I just did measure the transistors with my multimeter in diode mode. According to the data sheet, they are NPN transistors with the base on the left leg, the collector in the middle, the emitter on the right.
Left transistor I get a reading of 0.501 on the collector and 0.370 on the emitter. Right transistor reads 0.498 on the collector and 0.368 on the emitter. Please see photos attached.
That means they test good, correct? Or am I missing something?
Cheers,
sev

 

[curtisw99]

Hello curtisw99, thank you for your answer!

I just did measure the transistors with my multimeter in diode mode. According to the data sheet, they are NPN transistors with the base on the left leg, the collector in the middle, the emitter on the right.
Left transistor I get a reading of 0.501 on the collector and 0.370 on the emitter. Right transistor reads 0.498 on the collector and 0.368 on the emitter. Please see photos attached.
That means they test good, correct? Or am I missing something?
Cheers,
sev

Is it open "OL" between emitter and collector?

 

[sevi]

Is it open "OL" between emitter and collector?

When I put the positive lead on the collector and the negative lead on the emitter it shows OL in both transistors. When I reverse to negative on collector and positive on emitter, it reads 0.584 for the left transistor and 0.647 on the right one (please see photo attached). Is that the way it should be?

 

[curtisw99]

When I put the positive lead on the collector and the negative lead on the emitter it shows OL in both transistors. When I reverse to negative on collector and positive on emitter, it reads 0.584 for the left transistor and 0.647 on the right one (please see photo attached). Is that the way it should be?

It should be OL in both directions
Looks like they might be shorted

You should do all the final checks with them desoldered. Sometimes checking in assembly will give false readings

 

[SaturationPt]

Have you looked at the current draw of the motor? I'm assuming that it is turning freely.

 

[sevi]

It should be OL in both directions
Looks like they might be shorted

You should do all the final checks with them desoldered. Sometimes checking in assembly will give false readings

I will desolder them and check. Thank you!

 

[sevi]

Have you looked at the current draw of the motor? I'm assuming that it is turning freely.

Hello SaturationPt, I have not. How do I do that? And yes, the motor is turning freely. The turntable is working perfectly fine except for this weird overheating thing...

 

[SaturationPt]

I’m not familiar enough with TT drive motors to know what it should draw, but an ammeter in series with the motor is how you’d measure the current draw.

 

[sevi]

It should be OL in both directions
Looks like they might be shorted

You should do all the final checks with them desoldered. Sometimes checking in assembly will give false readings

So I desoldered the transistors and now they both show OL in both directions (please see photos attached). That means they are good, correct? What could cause them to run that hot then?

 

[curtisw99]

So I desoldered the transistors and now they both show OL in both directions (please see photos attached). That means they are good, correct? What could cause them to run that hot then?

You’ve got a bad component somewhere else.
If you can, check voltages from the service manual.
Or maybe just recap the board

Pardon Our Interruption...

 

[Gigantic]

You’ve got a bad component somewhere else.
If you can, check voltages from the service manual.
Or maybe just recap the board

Pardon Our Interruption...

I recommend recapping the board. I have a DP-37F of similar vintage, at somewhere around 45 years-old, these decks are on borrowed time with regard to the capacitors. Mine started out not holding speed until it warmed up, the eventually stopped maintaining a constant speed altogether. There's a vendor on the auction site who sells recap kits, they're not terribly expensive and pretty straightforward to install. It doesn't even have instructions, but it's a simple matter to recap the board, which is well labeled, simply desoldering a cap and replacing, being mindful of polarity. It takes about 2 hours to replace them all.

 

[sevi]

You’ve got a bad component somewhere else.
If you can, check voltages from the service manual.
Or maybe just recap the board

Pardon Our Interruption...

Yes, there must be a bad component somewhere before the transistors, but which one? I did a full recap of the motor board but to no avail. I read that bad ICs can cause transistors to overheat but in order to check if an IC is bad you need an oscilloscope as far as I understand. I don't have an oscilloscope and would not know how to use one right of the bat anyway. I could check voltages with my multimeter but I am no clear about what the voltages should read when looking at the service manual. Could you tell me where to check exactly and what the voltage should be? I tried uploading the service manual but it is too large of a file, so I attached two JPEGs of the motor board schematics only.

 

[sevi]

I recommend recapping the board. I have a DP-37F of similar vintage, at somewhere around 45 years-old, these decks are on borrowed time with regard to the capacitors. Mine started out not holding speed until it warmed up, the eventually stopped maintaining a constant speed altogether. There's a vendor on the auction site who sells recap kits, they're not terribly expensive and pretty straightforward to install. It doesn't even have instructions, but it's a simple matter to recap the board, which is well labeled, simply desoldering a cap and replacing, being mindful of polarity. It takes about 2 hours to replace them all.

Hello Gigantic, and thank you for chiming in! I did recap the motor board with a kit from an eBay seller I had bought other recap kits before. It didn't help, the transistors still get very hot. The kit was a complete recap kit for the DP52F but I only recapped the motor board as I did not think the arm control board could have any effect on the transistors in the motor board. Was that a mistake? Could bad capacitors in the arm control board cause transistors in the motor board to overheat?

 

[curtisw99]

Yes, there must be a bad component somewhere before the transistors, but which one? I did a full recap of the motor board but to no avail. I read that bad ICs can cause transistors to overheat but in order to check if an IC is bad you need an oscilloscope as far as I understand. I don't have an oscilloscope and would not know how to use one right of the bat anyway. I could check voltages with my multimeter but I am no clear about what the voltages should read when looking at the service manual. Could you tell me where to check exactly and what the voltage should be? I tried uploading the service manual but it is too large of a file, so I attached two JPEGs of the motor board schematics only.

Wherever the service manual shows a voltage, measure that spot on the board. Also, measure each side of the diodes. You should see different voltages on either side of a diodes.
When get to a spot where the voltage is way off, that’s where start testing components.
Make sure to use a dim bulb tester.


P.S. were the transistors hot before the recap? If not, did you put a cap in backwards?

 

[sevi]

Wherever the service manual shows a voltage, measure that spot on the board. Also, measure each side of the diodes. You should see different voltages on either side of a diodes.
When get to a spot where the voltage is way off, that’s where start testing components.
Make sure to use a dim bulb tester.


P.S. were the transistors hot before the recap? If not, did you put a cap in backwards?

Thank you curtisw99, I will look into that. And yes, the transistors ran hot before the recap, that's why I did the recap.