Penta 1, Hot, No-load current?

4 replies
J(
Offline
Jamian (archived2)
Bronze
Posted January 3, 2015 at 05:53 GMT
#2201702

Hi Guys,

Trying to see if I can get my Penta amps* working, without being too invasive.  I like to think less is more and reading some of the threads here I do not want to jump in at the deep end and try replacing a bunch of components, just to find the problem is still there.

The was getting really hot after a short amount of play time.  An EE at work told me it could be the No-load current and I see in the service manual how to make sure that is set correctly. Here is what happens when I try to do that -

Amp is completely cold; has not been on for weeks; nothing is connected to the inputs; it is set to Auto.  I plug it in; the light is green.  Placing the Voltmeter across 1R103 and 1R104 I start to try and get 30mV, but the mV continues to slowly rise...  ...Green light turns red.  Same every time I try.  Am I doing it wrong, or is it time to start replacing components?

I have tried to find a similar thread, but no luck.  Thanks for any advice you can offer.

-------

*Two came with the speakers.  One seams to work OK, the other had the input area pushed up in to the cavity snapping the PCB! (Does that happen often?).  Bought another second hand and this is the one that is having issues.

DI
Offline
Die_Bogener
Bronze
Posted January 3, 2015 at 10:32 GMT
#2201703

Not only no Inputs, also no Outputs.

It is normal that this adjustment voltage is rising when the amp becomes hot. But it must stabilize itself after some time.  The board is still mounted inside the Frame/cooler? The heat sensor is still pressed to the cooler?

I would tend to replace the caps... and the Potentiometer.

J(
Offline
Jamian (archived2)
Bronze
Posted January 5, 2015 at 05:06 GMT
#2201704

The is separated from the main speaker. No inputs connected; no outputs connected; The board is still in place and I am accessing from the bottom. I set the mode to Auto and then plug it in. 

Right now the amp is not getting hot (it was getting hot when connected up to source and speakers). It is flipping to standby (green, very briefly through amber, to red light) after around 35 seconds. During the time the green is on the voltage is rising slowly it never settles (doesn't have much time to settle, before flipping to standby and returning to 0mV).  I read that if set to Link and there is no input it will standby in 10ish seconds, but Auto is supposed to stay on for much longer. I have also tried this on the other amp that was not getting hot and it's doing the same thing, which makes me wonder if it's user error :)

I am game to replace caps and trimpots, but want to make sure I am fixing the issue and not simply adding nice new components to still get the red light after 35 seconds. Also want to make sure I am doing the simple task of trimming the no-load current correctly (even though the quick time out to standby and continually rising voltage means the task is not successful). 

Thanks for your help!

DI
Offline
Die_Bogener
Bronze
Posted January 6, 2015 at 08:52 GMT
#2201705

Many Pentas have a Problem with a broken board around the flap. The flat cable breakes the solder pins in this area. The pertinax board does not like tensions for a long time, the copper separates from the substrate of the board.

 

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