TRK 3D80 cap issues?

[hobbes748]

Good afternoon to you all,

I've got a 3d80 which I decided to add bluetooth to.

I dismantled it, soldered in the module, buttoned it back up - worked perfect. Really happy!

Two days later it started making a low humming noise when running off AC. It's fine on battery. The hum is constant and doesn't get louder or quieter with the volume. It hums regardless to whether it's on Tape/Radio/Dubbing/Aux

The bluetooth now also makes a slight high pitched whine (both on battery and mains) but only on Aux - which is where it's connected.

I dismantled it again, removed the bluetooth module (so no more whine) but the low hum is still present.

From the very little I know about electronics I was thinking either 'ground loop' or 'power supply capacitor' (although I'm leaning towards capacitor as the unit is back to stock again).

Whatever it is I'm assuming it's because I've pushed some component over the edge by adding the bluetooth.

Would anyone agree/disagree with my amateur diagnosis and (if it is likely to be caps) could someone tell me which cap(s) it is and should I replace with higher spec one(s) to take into consideration the mild increased in load?

Thanks in advance

 

[hopey]

There are filters you can get for the Bluetooth I think there called DC isolators. The tx maybe gassing due to age or ground loop sometimes from the tape head Cable.

 

[Superduper]

Try flipping the ac cord 180*.

 

[hobbes748]

Try flipping the ac cord 180*.

Hi,

Thanks for the suggestion. I'm not sure about other markets, but here in the UK the AC cable on this model isn't detachable, so flipping the AC would mean swapping the cables over at the plug.

As I've mentioned, I'm no electronics expert so I'm not sure if this fixed AC cord arrangement is just a design thing or whether it's out of necessity to protect the internals. Before I potentially go do something stupid, can anyone confirm that it'll be OK to swap the current round on this model?

Thanks again

 

[Superduper]

So, are you saying that the polarity of the cable is fixed at both ends (Boombox and wall plug)? If so, then just leave it. Some cable/Boombox use a system where the cable can be reversed. In that case, the hot/neutral wires are important and if reversed, can cause hum.

 

[lupogtiboy]

I'd make sure the plug is wired up correctly! Though the fuse in the plug or on your home circuit should blow if it's wrong

 

[hobbes748]

I'd make sure the plug is wired up correctly! Though the fuse in the plug or on your home circuit should blow if it's wrong

Yeah, it was wired correctly and I don't think the plug has been off in 20-odd years (which is about how long I've owned it for). It doesn't have an earth as per your diagram though. It's only a 2 core cable. Like I said, it's been working fine up until a few days ago. Grrrr!

 

[hobbes748]

So, are you saying that the polarity of the cable is fixed at both ends (Boombox and wall plug)? If so, then just leave it. Some cable/Boombox use a system where the cable can be reversed. In that case, the hot/neutral wires are important and if reversed, can cause hum.

Yeah, UK plugs have ony one orientation so the cable is fixed at both ends.

 

[Superduper]

It may be your AC Mains filter capacitor. It's located on your power supply board (or section of the main board). They are usually fairly large ones. As capacitors are relatively cheap this is a no brainer. Keep in mind that the power supply capacity is not governed by the quality of your capacitors and adding larger or higher spec'd ones will not increase the current carrying capacity. That is determined by the size of the transformer and the size of your rectifiers. Most bluetooth devices don't use that much power, but if it's not switched, then it's on all the time.

I would suggest replacing all electrolytic capacitors in your PS board. I changed all of the capacitors in the entire boombox on my Hitachi, it's not that many actually and fairly easy to do on this model.

 

[hobbes748]

It may be your AC Mains filter capacitor. It's located on your power supply board (or section of the main board). They are usually fairly large ones. As capacitors are relatively cheap this is a no brainer. Keep in mind that the power supply capacity is not governed by the quality of your capacitors and adding larger or higher spec'd ones will not increase the current carrying capacity. That is determined by the size of the transformer and the size of your rectifiers. Most bluetooth devices don't use that much power, but if it's not switched, then it's on all the time.

I would suggest replacing all electrolytic capacitors in your PS board. I changed all of the capacitors in the entire boombox on my Hitachi, it's not that many actually and fairly easy to do on this model.

Thanks Superduper, I really appreciate the assistance. Would you suggest replacing them like-for-like or should I put slightly higher capacity ones in instead?

 

[Superduper]

For the boombox as a whole, replace them with same uf caps, higher voltage and temps are fine. For the PS, you can probably get away with using slightly larger caps (value wise) if you like, but be aware that doing so will add additional stress to the transformer due to the inrush current during the charge cycle on higher uf caps will result in larger current surge. Typically, the next step larger can be 50% higher capacitance (i.e. 2200uf caps, next step up is going to be 3300uf) so that is substantial. Buy from reputable dealers only. I don't suggest getting from eBay or Amazon or anything like that. Made in China stuff are likely going to be subpar or seconds/rejects if they are sold on eBay or Amazon. Name brands are your best bet. For example, if you get Panasonic caps, you can't go wrong. But many folks are not familiar with the names of mainstream capacitor brands.... if in doubt, google the name and see what you get.

 

[hobbes748]

For the boombox as a whole, replace them with same uf caps, higher voltage and temps are fine. For the PS, you can probably get away with using slightly larger caps (value wise) if you like, but be aware that doing so will add additional stress to the transformer due to the inrush current during the charge cycle on higher uf caps will result in larger current surge. Typically, the next step larger can be 50% higher capacitance (i.e. 2200uf caps, next step up is going to be 3300uf) so that is substantial. Buy from reputable dealers only. I don't suggest getting from eBay or Amazon or anything like that. Made in China stuff are likely going to be subpar or seconds/rejects if they are sold on eBay or Amazon. Name brands are your best bet. For example, if you get Panasonic caps, you can't go wrong. But many folks are not familiar with the names of mainstream capacitor brands.... if in doubt, google the name and see what you get.

Thanks again!

I'll let you now how things go with it.