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This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
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
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
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.
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
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.
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
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.
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.
this is the item that shows the (tiny) lamp I am talking about.
As you know this is the lamp that sets the light-dependant resistors to work.
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.
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, becausethe circuit was made to mute the Beomaster in case the LDR housing lamp burns.
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.
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?
I found this on the internet: is it worth trying?
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.
The circuit diagram and part list doesn't show what bulb is used in the volume control circuit, but since all other bulbs in that unit are 12V, 1W (i.e. 80mA), I'd guess that B&O used the same in the volume control.
Go with the one closest to 12V/1W. If the 50mA bulb does cause problems, you could just take one of the original ones from the other buttons and replace it with the 50mA version. Those button bulbs don't have LDR's that expect a certain light intensity.Or even simpler, you could contact Martin. From other threads I know that he's offering sets of original replacement bulbs!
The LDR lamp is a difficult beast.It's much smaller than the front panel lamps, and I seem to remember it being an 8,6V type.It rarely burns, I think I have seen only two in all my time, and I'm afraid I only have a few used original lamps in the dungeons.
Part# 8002293 (as mentioned above) is the complete LDR module.The lamp was not available separately.
I ordered these lamps, they arrived today: besides that the lamps may burn, would these 50 mA's do any harm to the LDR's?: the 35 mA's are bigger and can only be mounted, bunched up as on the first picture. the second picture shows how the 50 mA goes in. Before I go on I hope that someone has good advice.
placing the bigger lamp gives problem wthe height of the aluminium cover.
The lamp has to sit right in the middle.An equal amount of direct light on all LDRs is essential.
Dillen: The lamp has to sit right in the middle.An equal amount of direct light on all LDRs is essential. Martin
True! Ideally the bulb should sit right in the middle and radiate the same amount of energy onto each LDR. However, I find it hard to believe that this will have to be precision work. LDR's are not really hypersensitive and since an incandescant light source radiates the same amount of energy in all directions (except maybe for the base, which might create a shadow effect), it shouldn't be too much of a problem. If the light sensors were photo transistors with high gain, the placement of the bulb might be more critical.
I checked the circuit diagram: This volume control bulb is driven by +15V, regulated by a transistor, and it has a series resistor of 200ohm. When the transistor is fully closed you'd get a bulb voltage of 6.3V. That explains why this bulb rarely burns out; a 12V bulb run on 6V should normally have a long lifetime. (AND you shouldn't have to worry about the heat created by the incandescant because it actually only runs on 0.25W and not the full 1W as rated!)
Regarding size of the bulb, of course it must fit into the casing or else you have a problem. What is the size of the other 12V, 1W bulbs?? Is it the same as the original volume control bulb?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!If you don't want to do that, you could replace those 3 bulbs from PCB7 with the 12V, 50mA version so that you get identical light levels from all 3, and then you have 2 more original spare lamps in case the volume control bulb burns out again in future.
You can test how well your replacement bulb works before closing it up and putting it back where it was installed. But more about that later.
rgds, manfy.
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PS: Your description of bulb sizes is a bit confusing. Could you give us the diameter and height of all four of them (std. original 12V/1W bulb, volume control bulb, new 12V/35mA bulb and new 12V/50mA bulb)?
manfy: 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!
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 practicallyonly 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.
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 Jansse: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: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: https://archivedforum2.beoworld.org/forums/t/28521.aspx )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!
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.
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:
https://www.beoparts-shop.com/product/lamp-kit-beomaster-1900-1900-2-2400-2400-2/
Please don't give out wrong information.
Dillen: The Beomaster 1900/2400 front panel lamps are not 12V. They run on apprx 14V so 12V lamps wouldn't last long.
The Beomaster 1900/2400 front panel lamps are not 12V. They run on apprx 14V so 12V lamps wouldn't last long.
I believe that the voltages accros the lamps will not exceed the 11,25V on some lamps and even lower on the other lamps. According to the voltages mentioned in the diagram the maximum current is 0,068 A. With the resistors the voltages across the lamps are reduced to at most 11,25V (for the selection ones). Or I must have overlooked something. Given the voltages across R2 and R3, the current might be different, 68mA or 75mA.
You are welcome to fit 12V lamps and see how long they'll last (and how warm they will be).You could also save yourself the trouble and believe me. The original lamps were part # 8230046 (custom specs).At some point (read: when lamps with the original specs were no longer produced) B&O replaced them with part# 8230067 (12V 83ma = the closets they had) and that's when problems began. (And due to a typo some manuals state 12V 30mA which won't work).You can find many Beomaster 1900/2400s with original lamps still going strong, and you can also find some Beomasters that had some lamps replaced, and the replacement lamps have burned out already whereas their remaining original lamps are still fine. In many cases the replacement lamps will be a T5-wedge-socketed type or the "drop-shaped"-type also found in the Beogram 2200/2400-series, whereas the correct lamps were a T1-3/4 type.
Dillen: You could also save yourself the trouble and believe me.
You could also save yourself the trouble and believe me.
I was just surprised by your statement I quoted. And with a regulated powersupply combined with resistor is series with the lamps, it will not be that much voltage across a lamp.
Often lamps are mentioned in Voltages and powerconsumption. 12 Volts, 1 Watt gives you the 83mA menitioned. But the amount of itensity will always be a surprise. It's obvious that a brighter lamp will have a shorter lifespan than a more dimmed version. The challenge is to use a lamp with enough brightness for which it's used and draws enough current for proper functionality of the master . Often the BM1900-2400 have (replaced) lamps where the red coloured plastic covers are dried out by the (too much) heat the lamps have produced over time and doesn't has the red colour anymore.
I know you have the correct lamps, it saves time and money for the ones who needs them and gives them a reliable solution for the years they want to use their with less bothering about the lamps. I see a similarity with cheap capacitors often used when recapping is done without concerning about the quality of them.
The most exciting moment for a lamp will always the moment when it will be switched on..
Dillen: and the replacement lamps have burned out already whereas their remaining original lamps are still fine.
and the replacement lamps have burned out already whereas their remaining original lamps are still fine.
The ones remaining are mostly the ones less and not to it's limit used. And of course the build quality of the replaced lamps will certainly have infuence on that.