Beomaster 1900. Standby LED on but nothing else. Lots of work done so far but no progress

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FredFredson Posted: Sat, Sep 14 2019 2:57 PM

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Hi all.

I've a Beomaster 1900 here that only has the standby led lighting up. If I press any touch buttons, the LED flickers (and it constandly flickers if I hold my finger down on any touch buttons)

Nothing works or powers up, no click from the relay, no lamps, nothing.

So far I have:

1. installed full new lamp kit

2. installed full cap kit

3. replaced IC9

4. replaced relay

5. replaced rectifier.

I read about testing TP15 for 15v with a multimeter but mine only measures a few millivolts. Is this because it's in standby mode or should this always measure 15v? 

Any ideas?

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solderon29 replied on Sat, Sep 14 2019 4:03 PM

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TP15 is the output of the electronic switch.It's zero voltage in stand-by,and 15 volt when the unit is on.

You need to investigate whether TR31 is trying to switch on?

It seems to be if the stand-by light is flickering when you keep a finger on any of the touch zones.

Are you confident that you have installed all the cap's correctly,and that there are no solder blob shorts on the pcb anywhere?

There is a fault detector system in the Beomaster which will prevent the electronic switch from working if a fault,particularly in the main amplifier occur's

Nick

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FredFredson replied on Sun, Sep 15 2019 7:54 AM

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I'm 100% on the cap polarity. This was the issue before I started work on it and all the changes made so far have been in an attempt to fix the unit.

Thanks for the tip in the tr31. I've ordered a replacement as well as a replacement for tr27.

Does anyone know where the component d50 is on the pcb? I've read on this forum about people replacing d50 to fix power issues but cant find the component location on pcb...

Also, would anyone have a photo of where on the board is the best point to place the multimeter probe for ground when measuring DC voltage and AC voltage? I'm getting the below readings for tr27 and 31 with the gnd I'm using right now. Can I use the same gnd point to measure AC?

According to Martin tr27 readings are way off so this may well be the culprit.

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solderon29 replied on Sun, Sep 15 2019 10:40 AM

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TR27 collector is certainly low,it should be at least 15 volt in standby and when the unit is on.

You need to investigate TR27,28,29 and C92.Although the supply at the emitter of TR27(23v) is normal,it's worth checking D50,the square bridge rectifier next to C92(2200uf)If this is the rectifier that you refer to earlier,is it fitted in the correct polarity?

D50 is a common failing in these Beomaster's,and if it looks as though it hasn't been changed,ie no fresh soldering since original),it's well worth replaceing it anyway.

I'm still suspicious of the fault switch though too.Not the switch system itself,but that something is triggering it?

Check the main output transistors IC200/201 and IC300/301) for leakage or short circuit?

For voltage checks,connect your meter negative clip to any metalwork,or to the negative connection of C92.

Nick

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Dillen replied on Sun, Sep 15 2019 11:11 AM

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solderon29:

TR27 collector is certainly low,it should be at least 15 volt in standby and when the unit is on.

It was the B-E voltage, that first sprung in my eyes.
R147 is what provides the voltage at the collector then, changing with the load.

Martin

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FredFredson replied on Sun, Sep 15 2019 11:33 AM

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Thanks for all the help guys

TR27 is definitely faulty. I took it out of circuit and tested with the multimeter in diode mode to confirm: I get a small voltage reading measuring from C to B but it's OL for E to B.

I'll try find a D50 to buy onlne. Does anyone sell a "D50 + transistor kit" for the beomaster 1900 series?  I bought the TR27 and TR31 already yesterday from RS online but they are coming in a tube of 20 each as that's the minimum order :D

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FredFredson replied on Sat, Sep 21 2019 1:15 PM

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I replaced the faulty tr27 with new, power it up and now I don't even get the standby light  

Checked the fuses, checked the 2x stiff copper wires attached to the board. Tr27 has 22v on E and B, with 0 on C.  Put back in old tr27 and still no standby light. I've obviously caused something else to fail somehow.

Any more tips from the grand masters here

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Dillen replied on Sat, Sep 21 2019 3:39 PM

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Did you remember to insulate the new transistor?

Martin

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FredFredson replied on Sat, Sep 21 2019 4:50 PM

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Looks like it is but I'll order some new insulation pads and washers just in case.

Cheers Martin for the advice

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FredFredson replied on Sat, Oct 5 2019 2:41 PM

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More work on this this morning.

The nylon washer and pads arrived during the week. Before I took tr27 out I tested continuity with a multimeter and sure enough, the screw on top had continuity with the centre pin on tr27. I scraped a bit of the black paint away from the bottom of the unit and found that it had continuity too. Martin you were 100% correct this was the issue.

Once I swapped the washer and pad there was no longer any continuity with the screw or bottom so all is good.

I also replaced the d50.

Powered it up aaaaand.... I see a little flash at the small 2A glass fuse blowing

I thought maybe the new transistor was bad from the previous session so I swapped that out with a spare one, put in a new fuse and it blows again immediately. I even put back in the original (known faulty) transistor and the fuse still blows.

Any ideas on what would cause this fuse to blow? It's the 2a fuse just above the d50.

Is it possible to install the d50 wrong? It's just a square block but is there a special orientation for it to be installed? One of the corners on the new one has a notch but the original one taken out was a perfect square.

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Dillen replied on Sat, Oct 5 2019 4:31 PM

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FredFredson:

Is it possible to install the d50 wrong? It's just a square block but is there a special orientation for it to be installed? One of the corners on the new one has a notch but the original one taken out was a perfect square.

Yes!
Very much so!
It has two alternating current (AC) inputs
and positive and negative (+/-) outputs.

Martin

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FredFredson replied on Sat, Oct 5 2019 6:29 PM

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Thanks Martin. I didn't see any obvious markings on the pcb to indicate the orientation placement for d50 but found this photo on the forum that shows the notch part is to be placed on the bottom left:

https://archivedforum2.beoworld.org/cfs-filesystemfile.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.50.76/IMG442592510.jpg

Once I did that the unit powers up and all looks good at last

Thanks for all the help