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BM1900 testing signal throughput

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Aad Jansse
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Aad Jansse posted on Thu, Mar 19 2020 10:12 AM

Apart from questions in other threads pertaining to the various issues I have with a couple of BM1900s, I would like to know if it is possible, without using a signal generator, to see any activity on a scope, e.g. the signal from a connected tape or record player?

Aad

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Dillen
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Answered (Verified) Dillen replied on Sat, Mar 21 2020 3:56 PM
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What John just said, 

- And the tuning discriminator lights won't work correctly with LEDs instead of the correct lamps (they will just light up instead of varying their light to help tuning in on a station).
- And the bleed-down of the 15V supply work correctly with LEDs fitted to the tonecontrol illuminations, causing intermittent (or permanent) problems going into standby
- And the muting at source-switching won't work correctly with LEDs fitted at the source indicators (often causing permanent muting).

As John just said, I can supply a kit with the correct lamps.

Martin 

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Dillen
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Dillen replied on Thu, Mar 19 2020 10:39 AM

Yes, you should be able to see any signal.
The good thing about using a signal generator is that you can expect a constant available signal in both channels at a constant frequency and amplitude.
Good for finding level problems by f.e. comparing left and right channels.
Music from a tape or a record can vary a lot in amplitude and content but would still be fine for finding where a signal gets lost.

Martin

Aad Jansse
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Nice to know now: I could borrow this "old school", Russian, scope from a friend who inherited this thing from his father but has no idea how to use it, neither do I; would you be so kind as to show me what the position should be, for doing the above mentioned measurement, of the various knobs and buttons.
Meanwhile i would like to get some advice as to the problem with the volume control, part nr 8002293, it appears that the lamp in it is faulty.
Is there a possibility to fix this (a new lamp or a white LED)? I may be able to close the housing light-tight again.


manfy
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manfy replied on Sat, Mar 21 2020 2:26 PM

Are you asking this because you can't read the labels on the buttons and knobs or because you've never used a scope before?

Regarding signal generator, you can find some fairly good free signal generator software on the net. If you have a high quality soundchip on your notebook it works quite well, albeit only for audio frequencies from 20Hz to 20kHz

rgds, manfy

sonavor
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Aad Jansse:

Meanwhile i would like to get some advice as to the problem with the volume control, part nr 8002293, it appears that the lamp in it is faulty.
Is there a possibility to fix this (a new lamp or a white LED)? I may be able to close the housing light-tight again.

No LED substitute for the volume lamps. The incandescent lamps are part of the volume circuit and affect its function. You can contact Martin (Dillen here on the forum) for new lamps for the Beomaster.

-sonavor

 

Dillen
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Answered (Verified) Dillen replied on Sat, Mar 21 2020 3:56 PM
Verified by Aad Jansse

What John just said, 

- And the tuning discriminator lights won't work correctly with LEDs instead of the correct lamps (they will just light up instead of varying their light to help tuning in on a station).
- And the bleed-down of the 15V supply work correctly with LEDs fitted to the tonecontrol illuminations, causing intermittent (or permanent) problems going into standby
- And the muting at source-switching won't work correctly with LEDs fitted at the source indicators (often causing permanent muting).

As John just said, I can supply a kit with the correct lamps.

Martin 

Aad Jansse
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Wonderfull to get all this advice.
As to the lamp issue : Dillen told me some posts ago what to do and not. what my question about the lamp replacement by a LED can be clarified by a picture that missed my previous post; here it is now.

As to the scope:I used once, a century ago, a scope, but my borrowed one has an usermanual in German which language  is much les than my English.
What I actually want to know:  could I do any harm to the circuits when I put the probe on whatever place in a pcb and then start pushing and turning knobs and buttons.

 


Aad Jansse
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this is the item that shows the (tiny) lamp I am talking about.

Aad


Aad Jansse
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As you know this is the lamp that sets the light-dependant resistors to work.

manfy
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manfy replied on Sat, Mar 21 2020 7:15 PM

Aad Jansse:

As to the scope:I used once, a century ago, a scope, but my borrowed one has an usermanual in German which language  is much les than my English.
What I actually want to know:  could I do any harm to the circuits when I put the probe on whatever place in a pcb and then start pushing and turning knobs and buttons.

No worries. Provided that the oscilloscope still works as it should, you can't damage anything on the circuit.

One important thing you have to keep in mind:
The ground terminal on the probe is usually earthed !!! So, if you carelessly attach it to the wrong part on the 240V side, you'd trip the RCCB (ground fault protector) in your house.
Just steer clear of the 240V side of your device. You'd need a 1:20 probe or bigger to measure anything on the grid side of the circuit anyway.

If I were you, I'd familiarize myself with the scope function on some other signal before starting on the BM1900 (e.g. the signal from headphone connector of your PC/notebook that will supply the signal from the signal generator software). Google translate will help with translating the labels on the scope and you should be able to find quick tutorials on how to use a scope on the net.

 

Dillen
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Dillen replied on Sat, Mar 21 2020 7:57 PM

LEDs cannot always replace incandescent lamps.
Keep in mind that, where incandescent lamps have a certain lag in the form of glowing metal, making them provide a pretty constant amount of light output, LEDs are (hard-working) diodes flashing at at very high frequency. They are not emitting a constant light.
Not all LDRs and other light sensors - and their respective circuits - are built for this, and electronics can get confused by the constant on/off switching.

My advice; Take that LED out of the LCD housing and fit the lamp (or a new lamp) back.
Not everything modern is necessarily better.
LEDs are not always smart, and LEDs do no necessarily last longer.

BTW; Did you change the lamp current monitor circuit to suit the current draw of the LED?
If not, you will have a problem with the muting circuit, because
the circuit was made to mute the Beomaster in case the LDR housing lamp burns.

Martin

Dillen
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Dillen replied on Sat, Mar 21 2020 8:01 PM

Aad Jansse:

As you know this is the lamp that sets the light-dependant resistors to work.

The lamp is controlled by the volume control circuit.
More light = lower volume (2x LDR).
More light = more Loudness (the other 2x LDR).

Throw that LED away.
LEDs and lamps are not the same type of component.

Martin

Aad Jansse
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I am overwhelmed by all the information, thank you for this lesson, however, I am sorry for not mentioning that I have not already actually replaced the lamp by the LED., I just wanted to make sure that I would not make a ignorant move; therefore the remaining question is now: can I acquire somewhere such  a tiny lamp and restore this unit 8002293?

Aad

Aad Jansse
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I found this on the internet: is it worth trying?

Aad


Aad Jansse
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There are also lamps available, 12V/ 50 mA, which one will suit best? As to the size, this one looks better, however the mA’s differ.

 

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