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Beomaster 4400 power-amp problems or ?????

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ALF
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ALF posted on Tue, Feb 7 2017 9:46 AM

Hi everyone !

I am in the middle of restoring a BM4400:

So far all electrolytics have been replaced incl the two big ones.

Both output trimmers have been replaced with 25-turn new ones

All output amp TIPs have been replaced with TIP142/147 and The BD-165 with BD-139

And YES,  they were all conected the correct way - even with some of the short brown wires crossed :-)

All TO-92 transistors in the power-amp section have been replaced together with D101,102, 103, 104

IC3 together with TR15-16 and D22 in the fault switch have also been replaced.

TR1 and TR2 have been replaced

A long list of resistors - as suggested by Martin and Menahem - has been replaced as well.

Turning on the unit via, the DBT shows as follows:

Without P11/12 connected the DBT briefly illuminates, goes out, overload bulb does not illuminate, RL1 does not engage.

With P11 or P12 or both connected the DBT briefly illuminates, the RL1 engages, DBT goes out.

What am I missing here ? 

The PCB has been inspected with a strong magnifier for cracks, but 'negative' - no cracks to be visible !!

Is it likely that the RL1 is faulty ??

Replacing so many components was not only easier but in my opinion sensible, as desoldering, testing and

putting them back in would have reintroduced worn-out parts.

Is it worth taking out the RL1 ??

Any help/suggestions is more than welcome :-)

ALF

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Dillen
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Verified by ALF

Any DC on the output rails?

Martin

Lonnie
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Hi ALF,

I noticed in your picture P1010148 that you may have crossed over the C&E leads from the board to the TIP147 - 0IC202.

The manual shows the layout from the bottom view which has ECB from left to right. When you flip it over to get the top view perspective you will have BCE from left to right. You have B going to B, C going to E and E going to C???? You may need to double check this as the manual may be wrong but also the printed boards are often wrong. If the manual is correct then the leads should not be crossed over. I don't have a BM4400 so I can't do a physical check for you. Maybe someone else can?

Regards

Lonnie

 


Craig
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Alf

As lonnie quite rightly points out....the printed boards and circuit diagrams can contain some inconsistencies and therefore its always best to replace components in the same orientation as they came out, after all they worked  that way for forty years or so, have a look at the picture of one of mine, it shows from left to right OIC201/OIC202/OTR200/OIC203.....unfortunately OIC200 is out of shot, however the important thing to note is the clearly visable crossover of connections on OIC202.


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Craig
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Alf

I know you have changed out all of the transistors on your 4400 more than once, they cant all be shot. Get yourself one of these magnifying lamps and have a really close look on the solder side of your amp section, the more times you remove and solder a component the greater the chance of causing damage to the tracks, blobs of solder shorting etc.......


ALF
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ALF replied on Thu, Jul 27 2017 8:16 AM

Nice suggestion 😳

I could not have done what I did without a magnifier 😁

Infact I have two 😸

Sadly to get affordable ones with a decent lence diameter one is limited in the magnification as you

Perhaps remember from your physics classes ?!

ALF

ALF
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ALF replied on Thu, Jul 27 2017 8:16 AM

Nice suggestion 😳

I could not have done what I did without a magnifier 😁

Infact I have two 😸

Sadly to get affordable ones with a decent lence diameter one is limited in the magnification as you

Perhaps remember from your physics classes ?!

ALF

ALF
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ALF replied on Thu, Jul 27 2017 8:17 AM

Nice suggestion 😳

I could not have done what I did without a magnifier 😁

Infact I have two 😸

Sadly to get affordable ones with a decent lence diameter one is limited in the magnification as you

Perhaps remember from your physics classes ?!

ALF

ALF
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ALF replied on Thu, Jul 27 2017 8:17 AM

Nice suggestion 😳

I could not have done what I did without a magnifier 😁

Infact I have two 😸

Sadly to get affordable ones with a decent lence diameter one is limited in the magnification as you

Perhaps remember from your physics classes ?!

ALF

ALF
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ALF replied on Thu, Jul 27 2017 8:38 AM

Sorry Craig,

there was only one reply intented !

i do understand your concerns about multiple replacements of the same - I did inspect the board

several times for bridges with my illuminated 8-times magnifier......very exhausting but no bridge has been discovered !

the devil sits somehwere else ??!

ALF

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