manfy wrote:

If yes, you could take one from PCB 7 (bass/treble/balance indicator). They are just indicator lights and they don't fulfill any other function. Actually you could replace those 3 bulbs with LED's without adverse effect!

The three balance/tonecontrol indicator lamps are used to bleed down the 15V supply when going into standby.
If these lamps are burned the Beomaster can be very difficult to get into standby, because the 15V supply isn't bled down fast enough.
It will just click repeatedly as you hold your finger on the standby pad and go back on without any source selected.
I have removed many LEDs in Beomasters coming in here for repairs and put in the correct lamps.

Good quality lamps will last for decades, but if you absolutely must replace with LEDs, you should also introduce a suitable load (power resistor) to imitate the current flow of the original lamps - and then most of the idea of replacing with LEDs would be punctured in my opinion. 

As mentioned earlier, I seem to remember the LDR lamp being an 8,6V type. And yes, it's underrun so most will last a lifetime, they practically
only go bad from rough transport etc.
The lamp is a grain-of-wheat size and you'll be surprised how big a difference a little moving the lamp around makes to the volume etc.
It's just LDRs. yes, but they seem to be matched. You can't always just take an LDR from one case and move it to another without also moving its mate in the other channel.
Probably why this module was not available in separate parts - only as a complete and sealed unit.

I will be happy to dig around in the dungeons for a good used LDR casing if needed.

Martin

The newly acquired bulbs are of the same size as the original burn one. The other is a bit bigger. Since I have two of those PCB’s I have two options.

As soon as I go to my workbench I will go on with  this “project”; but this has to wait till sunset) I am now enjoying the sunshine in my garden, being grounded  because of the threat of the covid-19 virus; luckily I am allowed to keep less than 1 1/2 m distance from my Beo’s, the Beo virus is harmless)

By the way I had already replaced the bulbs in the treble-,  bass- and balance area  of my 1900 and 2400 by LEDs and that looks good.

As usual I am gratefull for the responses, they give some consolation in these hard times.

Aad

Aad Jansse wrote:

By the way I had already replaced the bulbs in the treble-,  bass- and balance area  of my 1900 and 2400 by LEDs and that looks good.

Hmmm....  But when I compare this with Martin's statement:

Dillen wrote:

The three balance/tonecontrol indicator lamps are used to bleed down the 15V supply when going into standby.
If these lamps are burned the Beomaster can be very difficult to get into standby, because the 15V supply isn't bled down fast enough.
It will just click repeatedly as you hold your finger on the standby pad and go back on without any source selected.
I have removed many LEDs in Beomasters coming in here for repairs and put in the correct lamps.

I'm wondering: Isn't the self-powerup exactly what you said happened with your system? So maybe the uP board was less of a problem than this modification?

Did you install power resistors parallel to the LEDS in order to get to the 60-70mA for each indicator light? A normal LED is usually run with 20mA. Even if you have 2 in parallel, you're still short of the current needed to quickly bleed the 15V supply on power off and you could see odd problems. What current does a single LED replacement draw on that PCB 7?

---------------------
[edit} Oops, sorry! Different thread! You're not the one who had the self-powerup issues.

Nevertheless, modifying the LED lights so that they draw some 60-70mA might still be a good idea to avoid future problems!

And here's how you can test the function of your volume control:

1) verify that the LDR's are good:
-) measure the "dark resistance": cover the LDR's and measure the resistance of every LDR. All components should show similar resistance of several hundred kiloohms, maybe even higher.
Pls note that it may take several seconds for the LDR's to reach their "dark resistance" after exposing them to darkness

-) measure the "light resistance": expose the assembly to a bright light source (e.g. 60W light bulb in close vicinity or a flashlight or similar). All components should show a similar resistance of around 300 ohms or below.

2) test the chosen light bulb:
-) mount the bulb and close the cap on the volume control. Apply 6.3 VDC to the bulb (with an external power supply). Now measure the resistance of all LDR's. It should be in the range of 300 ohms.

(The information about 300ohms is taken from this thread: /forum/imported-unmapped/beomaster-1900-optoelectronic-volume-control-repair )
If the light resistance is much higher than 300ohms, the chosen bulb is too dim and you need to use one with higher current rating. If that's not an option, you could also change change the current limit resistor R138 from its original 200ohms to a smaller value, provided you're comfortable with the very basics of electronics (e.g. Ohm's law V=R*I, and similar)

Please let us know the results of the LDR measurements dark resistance and light resistance!

rgds, manfy

First the good news : at this moment I am listening to a radio broadcast produced by the BM1900 in hand!!!!!! 
After a test of the LDRs, with positive result, and subsequently having  mounted the  smallest bulb and having placed this volume control unit I could not suppress a loud “HALLELUAH”.

Despite the advice with regards to the lamp/LED switch it turned out that this LED lighting does not create any disturbance.

Nevertheless I am grateful for all the lessons in this thread.

My newly revived 1900 contributes a little to endure the restrictions of the current Corvid-19 crisis lock-down.

Hopefully we will “ meet “ again because I have more patients waiting for a place on the workbench.

aad

I can supply the correct lamps - both for the front panel and for the LDR casing.
PM or email me.

Martin 

The Beomaster 1900/2400 front panel lamps are not 12V. They run on apprx 14V so 12V lamps wouldn't last long.
And they are not 50mA - it's far too little current for the balanced lights in the volume and tuning indicators to function correctly.
Besides, the wattage is also important for the source indicators, since they also pass a little current when not lit as they form part of the circuit muting briefly while switching source.

The lamps are critical for correct functionality of the Beomaster.

Correct lamps here: