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Beomaster 1900-2 won't power on

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Brokenstereo
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Brokenstereo posted on Wed, Feb 17 2021 10:27 PM

Hi I have a beomaster 1900-2 that wont power on after I recapped it, replaced the rectifier and replaced the emitter resistors as 2 had gotten far too hot

My first issue I have no idea what wire is live the black or blue?

Then after that where should I look?

I have a meter but not overly sure how to use it for testing components really any help really really appreciated.

 

 

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sonavor
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Okay but don't continue until you replace TR27.  The +15VDC power supply needs that.

I am going to guess that the -31VDC filter capacitor incident was the root cause for the TR200-TR301 Darlington failures.
There could be other problems so check out the other components that connect to the +-31VDC rails.

-sonavor

 

sonavor
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One other thing...
When you replace the power transistors do not try to turn the Beomaster 1900 on without mounting those transistors to their heatsinks (with proper thermal insulators).  

-sonavor

Brokenstereo
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wont normal cpu thermal paste be ok ?

ive ordered upgraded darlingtons 142 and 147 as they were easier to get hold of  and a bunch of tip32c mine had a 32A fitted but i couldnt get that easily

and a new pair of 5600 caps

sonavor
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I think a lot of the cpu thermal paste is conductive.
On the transistors that press against a heatsink with a spring such as the Beomaster 1900/2400 I have been using Sil-Pad product for the thermal conductivity. When I don't use the Sil-Pad production I use Wakefield 120 white thermal paste.

-sonavor

Brokenstereo
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ok ordered some of those too

Brokenstereo
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Just put in a new tr27 and I still have standby only krps it on for a few seconds as it wasn't heatsinked 

 

Brokenstereo
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hi anyone any idea what gauge wire i should be using for replacing the black wiring in the unit just need to extend/replace 1 or 2 bits also what gauge wire is used on the switch as they could do to be made a bit longer too

 

 

sonavor
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Are you referring to the speaker terminal wiring?

-sonavor

Brokenstereo
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hi its back on and stays on in standby  but as soon as i take it out of stand by it goes straight back to standby

Brokenstereo
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yes i was

as for the switch ones i just cutup a power cable :)

sonavor
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Do you hear the protection relay click when it does that?

It sounds like your Beomaster 1900 has more faults in the output amplifier section than just the power transistors that you found damaged. The blown -31VDC filter capacitor incident likely did more damage.

-sonavor

Brokenstereo
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yes relays click  if i do it with the caps off it stays out of standby

sonavor
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Okay, then you have some work cut out for you regarding finding the failed components.  A big task I know but it has to be done.

-sonavor

Brokenstereo
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interestingly i took it out of the case again connected everything back up and it turned on and stayed on!

just broken the power switch tho snapped a tab off

gonna try it back in the case

Brokenstereo
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huge update

its working !

 

i just tried to set the idle voltage though and i dont seem to be able to get any results that make sensethe measurement is bouncing around all over the place it doesnt stay still an as soon as i touch the pot it changes even more

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