6060 running hot

[tweedsmith]

It's been a long journey with this 6060, mostly centered around the 2647 Driver board. After replacing the 2SA726 Transistors and a recap of that board, I get clear sound on all inputs from both channels and the bias on both sides adjusts to in spec per the service manual. I'm not sure if the 6060 has a way to check/adjust the offset (and if fact when I've tried to research it seems I see bias and offset used in the wrong context or interchangably - at least as I understand it from the service manual for the bias adjustment)

Everything sounds good in my testing, but I'm wondering about the fact that the heat sink is too hot to touch for more than a second or two, and with the lid on, the metal grate is pretty hot as well.

My main questions are:

1. Is it normal to run that hot?
2. If not, how can I start troubleshooting the source?
3. What is the best way to measure the DC offset
4. If the DC offset is off, is there a way to adjust that or replace components to improve the reading?

Thanks, you folks are always appreciated.

 

[AlTinkster92]

My 2 cents, yes if you cant touch the heat sink for more than a second then somethings running too hot. Turn it off and don't use till it gets figured out. My bone stock 8080DB can run for hours and the heat sink never gets hot, only very slightly warm if that. Hope you get it figured out.

 

[petehall347]

are you measuring 15mv across both emitter resistors ?

 

[tweedsmith]

are you measuring 15mv across both emitter resistors ?

Yes, it measures correctly there.
I wonder what can cause it to run so hot?

 

[Hyperion]

I wonder what can cause it to run so hot?

Something is wrong, with your measuring method, or your meter. You must not use the 6060 until you find out what the issue is, as it will be seriously damaged by doing so.

 

[Hipocrates]

I wonder what can cause it to run so hot?

Other than high bias...
Heavy load (demanding speakers, too loud, 4 speakers at once )
High frequency oscillations

 

[tweedsmith]

Something is wrong, with your measuring method, or your meter. You must not use the 6060 until you find out what the issue is, as it will be seriously damaged by doing so.

Thanks all. This post cause me to rethink, and I chanced turning it on to check my measurements - there was a mistake there. I feel foolish, but glad I asked here. It's running cool now and sounds good through the aux input.

 

[Scott Muni]

Thanks all. This post cause me to rethink, and I chanced turning it on to check my measurements - there was a mistake there. I feel foolish, but glad I asked here. It's running cool now and sounds good through the aux input.

Sharing your mistake will help others learn. There is no shame in mistakes, we all make them.
So what did ya do?

 

[tweedsmith]

Sharing your mistake will help others learn. There is no shame in mistakes, we all make them.
So what did ya do?

One problem I had is that I replaced the trimmers so my reading wasn't even close to start as a reference. I triple-checked my meter settings and saw I had the adjustement way high. My advice to other newbies would be get to know your meter better before diving in.

 

[Sdp81]

Comprobar tr1 /tr2 2sc945