Help! Is my tuner overheating?

[Kuja]

Hello,

Few months ago I got a mint Kenwood KT-917 from eBay.

When it arrived, I hooked it to my amp and turned it on - everything worked flawlessly except for the DDL LED not being lit when a station is tuned.

Since I didn't have a rack that it could accommodate it, I didn't immediately start to use it.

Few days ago, I finally had time to build the rack.

I put the KT-917 in it and I started to listen to some music.

After some time I noticed that the tuner started to be quite warm.
After some three hours the top of its metal case got almost burning hot - when I had a palm of my hand on it, it didn't feel comfortable at all!
I had a sensation of almost being burned.

Even the tips of rotary controls were warm, as was the front glass...

Here is the pic of KT-917's initial placement in my rack:

I figured out that ventilation might not be sufficient, so I increased the space above the tuner like this:

The situation got much better - after few hours the tuner's top surface got quite warm, but not unpleasantly hot.

When I tried it in the open, out of the rack, after few hours it was only lukewarm.

So far I only had slim digital tuners and this is my first monster analog one, so I don't know if this is normal.

It has all this lamps inside and a huge transformer and capacitors that could find a place in some amplifier.

If this is normal, how these things were supposed to be used?
In what kind of rack?

If it should get so warm, why doesn't it have some ventilation holes on the top of its case?

The heat build up is so excessive even in my rack that has all four sides completely open. Shelves are connected only by three threaded iron rods.

Or maybe some aged components inside are over heating?!?

On the other side, the sound that this tuner puts out is awesome, that it is hard to believe that there is something seriously wrong with it.

Thanks in advance,

Aleksandar

PS

I'm sorry because of waisting some space, but I'll put the same question in the Tuners AK section, in case that some "tuner" people are not visiting this forum.
I really need to know if something is wrong in order to prevent some bigger failure!

 

[Fred Longworth]

Generally, tuners consume very little power. A typical tuner will eat up less than 50 watts. That's why, unlike machines with power amps inside, tuners are normally sealed boxes.

If the entire tuner is getting excessively hot, here's what I would do. I would remove the cover and then turn it on. I would let it warm up for, say, 30-60 minutes.

Then, I would FEEL THE POWER TRANSFORMER. It should be warm, but not truly hot, and certainly not so hot your finger recoils.

If it is super hot, then you have a problem. Either (1) the transformer is becoming lossy and is on the way to burning out, or (2) the load on the transformer is excessive.

However -- and this is important -- if the tuner sounds and tunes excellently AND the transformer is super hot, then the load is probably not drawing excessive current.

Still, I would SWITCH THE MACHINE OFF, wait a few seconds, and then very carefully touch the heat sinks on the regulator transistors. They should be warm-to-hot, but certainly not so hot that they can blister a probling finger. Brush a finger against a suspect heat sink before fully touching it.

NOTE: TO AVOID SHOCK FROM UNDISCHARGED CAPACITORS WHEN TOUCHING PARTS ON A MACHINE JUST SWITCHED OFF, ALWAYS KEEP THE OTHER HAND BEHIND YOU AND AWAY FROM ALL CONDUCTIVE SURFACES.

If you find a heat sink that is extremely hot, then there may be excessive load current drawn through that regulator device.

Also, take a good look at the circuit boards. Excessive current draw -- and excessive heat -- are often associated with a brown discoloration of the circuit board.

Hope this is useful.

Fred Longworth

 

[nbourbaki]

I really can't tell in the second picture, how many inches of clearance do you have from the top of the tuner to the bottom of the overhead shelf? To me the first picture looks too close. Do you have any large heat sources like a big amp futher down in the rack that could be heating things up above? For something as valuable as that tuner, I would give it 6 inches between the top of the unit and the shelf above. As far as it not heating up out of the rack, it could be that you moved it where there is greater ventilation or away from other heat sources. Beautiful tuner :thmbsp:

 

[Kuja]

I opened the KT-917 today.

I followed Fred's advice - I left it turned on for one hour and then I started touching the components.

The transformer got very warm, but not on the unpleasant side - I can hold my fingers on it indefinitely.

On the other side, there are a couple of heat sinks that got extremely hot - I can not touch them longer than one second. I could seriously burn my fingers on them.

I took many photos and I marked red the heat sinks in question.

The transformer and those heat sinks are the only real sources of heat, everything else runs almost cool.

Here are the pics - what do you think?

 

[chillwolf]

Look at this pic you posted. (4th one) The three caps at the top center are in bad shape. The two on the right are deteriorating at the bottom and the one on the left is leaving scorch marks on the board. Maybe this is what is causing this tuner to run hot. Looks like a serious impedence to electrical flow here! JMO, I am in no way an electronics expert like many of the other fine AKers here. Also look at the eighth pic, there are two caps at the left center that are also burnt looking at the bottom.




Regards, ^WILL^^

 

[glen65]

Its normal for those areas you have marked as hot to be warmer than the rest of the areas in the unit. However they could be overheating. All electrolytic caps in close proximity of those heat sinks should be replaced regardless of their appearance. The resistors in those areas should have their value checked. There’s also the possibility that a couple of those transistors could be high in the leakage department. This would cause higher than normal current flow which would translate into more heat. In other words it needs a good thorough going through.

 

[Kuja]

Thanks guys for all your answers!

...The resistors in those areas should have their value checked...
...There?s also the possibility that a couple of those transistors could be high in the leakage department. This would cause higher than normal current flow which would translate into more heat...

Glen,

Can resistors change their values in time?
I always thought that only capacitors are susceptible to aging...

What exactly do you mean by "transistors could be high in the leakage department"?

Thanks a lot!

Aleksandar

 

[glen65]

“Can resistors change their values in time?”

They generally are not as susceptible to aging to the degree the caps are but given their location they should at least have their value checked. In some cases this may involve desoldering one side
of the resistor in order to get an accurate reading.

“What exactly do you mean by "transistors could be high in the leakage department"?”

When a transistor is in its off state it blocks the flow of current. Leakage is when you have an undesired amount of current flow during the transistors off state. When you have excessive leakage within the transistor it can cause higher than normal temperatures to be generated within the device.
If this is the case then the transistor would need to be replaced.

 

[Fred Longworth]

The regulators in your machine are high-power ones with big heatsinks.

At the very least, you should replace the capacitors where the jackets are beginning to peel down. As recommended above, I would replace ALL electrolytics in the immediate vicinity of the regulator heatsinks.

Sounds to me, though, like your machine is one of those units that simply runs hotter than most. I do recommend breathing space above the chassis. A small whisper fan can be purchased at most electronics parts stores, and can be used to blow fresh air over the top of the case. You may even wish to cut some small holes in the chassis to facilitate air flow. (If you do, use a drape to prevent metal particles from getting inside the set.)

NOTE: You have a VERY high quality machine!

Fred Longworth

 

[ron-c]

Those two caps next to D3 and D4 diodes are toast. Just write down all of the cap values on that board and buy new ones. I bet the whole job could be done for less than $20.00 in parts and you will have a much happier tuner.
Nichicon, Rubicon, etc. will all work.
Cool tuner you have, buy the way.

Thanks,
Ron-C

 

[chillwolf]

There's more than two bad caps in that tuner! I counted about 7 or 8 just from what I could see in the pics. (maybe more?) No wonder it's running hot!