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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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ALF
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not pretty, but it is what it is - a mess !


ALF
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more of the same


ALF
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ALF replied on Thu, Feb 16 2017 6:02 AM

if you would like to see pictures of a special location - please feel free to tell me

in the end it could only be beneficial !

cheers

ALF

ALF
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hello once again,

the pic I uploaded shows two of the old TIP141 darlingtons on the left side - also visible are the plastic washers

to isolate the TIP from the heatsink

on the right side two of the new ones installed without the plastic washer as I believe they are unneccessary due to integrated

plastic housing !!

am I correct with that assumption - a thought came up that the newly installed TIPs without plastic washers may cause the short

triggering the fault switch and RL1 ??

still have not yet discovered any other reason for the persisting problem !

let me know if those washers are still required ?!

ALF


sonavor
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The plastic mounting washer/grommet on the original transistors prevent the metal mounting screw from touching the metal plate of the transistor. On the new version of the transistors it looks like the plastic case has the plastic fit through the hole of the metal so it has a built in isolator for the mounting screw. The new ones don't need the washer/grommet.

ALF
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ALF replied on Fri, Feb 17 2017 10:14 AM

thanks John,

that is what I thought but then......simple oversights and the damage is done.

being so involved, one often doesn't see the trees in the forrest and I keep checking now for some time

with very little luck !

cheers

ALF

sonavor
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No problem and keep posting pictures with your questions like that. It makes it much easier to see what your question is when we can view the problem.

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

 


ALF
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ALF replied on Tue, Feb 21 2017 3:30 AM

hi lonnie,

thanks for that - incredible eye for detail !!!

this goes for each channel - I had two crossed for each side :-((

question is would those TIPs been damaged by the cross-wiring as my fault-switch

still activates the RL1 after I corrected the connections ??

ALF

Lonnie
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Lonnie replied on Tue, Feb 21 2017 6:40 AM

Hi ALF,

You may just want to confirm with your multimeter on the output device leads that you have continuity between:

Emitter of 0IC100 and Collector of 0IC101

Collector of 0IC102 and Emmitter of 0IC103

and repeat for other channel.

That should confirm that you have them wired up correctly.

 

I'd say you may have shorted one or a couple which would allow DC at the speaker which would trigger the fault signal.

Best way to check is disconnect the leads and test them.

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.


ALF
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ALF replied on Tue, Feb 21 2017 9:12 AM

Hello Craig,

Thanks for that !!

I have crossovers on both 0TR100/200 because they are fitted face-up !!!!!

Looking at the diagram 5-1 of the SM I would need a cross-over at. 0IC203/103 in order to realise connectivity to Pin4.....

Pin4 at P11 and P12 are connected to C of 0IC203 and to C of 0IC103 respectively.

am I wrong  or is it 'either crossover at 202 or 203'  ???

The connectivity check that Lonnie mentioned is ok !

Your thoughts ????

ALF

Craig
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Alf

I mounted my OTR100/200 face down so didn't need to crossover, this was how the originals where mounted so I went with what I knew, take a look at this picture from my basket case thead, I will take mine apart this evening and post some detailed pictures of all the darlingtons for you to compare your own connections......


ALF
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thanks Craig, that's most helpful :-)

please take a look at pic 1010197 from the SM 5-1

as Lonnie explained, you turn this over and compare the B C E marking from left to right at the top of the board at 0IC202 which is the next picture

you will see B E C from left to right.

I connected 0IC202 according to the ' B C E ' marking, meaning I do not have to cross-over wires......or am I completely nuts ?????


ALF
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have a look at pic 1010196

that is how I wired 0IC202 and also look at the marking on the board, which is different from the SM diagram 5-1


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