ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
When Peter dropped off his BM5000 for me to run some comparison checks he also left this monster with me, never had to lift anything so heavy! In an industrial setting one would need a lifting plan, risk assessment and method statement to move this from one room to another.....
Peter tells me it runs fine for a while and then gives out a "clicking noise" so I powered up and connected a turntable and speakers to it and gave it a whirl.....works fine, sounds very good....tried FM radio and that's all good too. Left the radio running and took a shower, came back and still all good....only one thing was unusual...the left channel side of the cooling tower was warm to the touch, the right side was quite cold.
I think I will take a look inside...maybe check the quiet current setting on the left side amplifier...probably check them both.
Opened up and put the primary panel into the service position....lots of accumulated dust and dead skin, removed the glass panel and there was even more, im surprised the tuning LED's could be seen through the covering ;¬)
Will give it a good clean before it goes back together, meanwhile lifted the secondary operating panel into the service position and exposed the left channel output amplifier board....someone has been in here before me and replaced a component or two....I can see two newish Panasonic caps and a replaced emitter current trimpot
The service manual sats connect a multimeter across the two emitter resistors 5R236 and 5R237 and adjust the pot 5R226 for a reading of 18mV....this was what I found....little wonder the left side of the cooling tower was running a little warm...…..
The major issue sounds like a relay clicking on and off once the thing warms up. Still plays but very annoying noise!!
Peter
Personally, I wouldn't trust that a bias pot alone throws out the idle current, there must be something else... and I see a lot of those red devil capacitors waiting to explode... maybe more...
You may well be right Charles.....however this pot is very sensitive, slightest movement deflects the mV level by a huge amount...got it close enough.
Got her powered up right now and have been listening to the radio tuner for around 30mins, both sides of the cooling tower are quite cold with the volume at 30%...….going to give it a good long soak
had the unit going for a good three hours, not stressing it however...just around 30% volume and on the tuner, and no signs of any errant relay activity...everything stayed really cool. Had a closer look at the left output board and the previous repair has indeed included most of the ROE caps, left one out oddly....I have a replacement to hand and also a 100 ohm 25 turn pot....so I will have a go at getting it out, as I have it so close its the right thing to do.
My previous BM8000 had been serviced under my ownership and I was presented with a huge back of old capacitors! This one came from another Beoworld member and had been serviced elsewhere. I should have videoed the errant behaviour of course!
No worries Peter....these things have an annoying habit of hiding in the shadows ;¬)
Removed the control panel to get at the amp board and take some pictures....mostly to ensure I know how to re assemble it!
Removed the heatsink
pulled out the six off spade connectors......
pic is always useful..
This all gave enough play to unclip the circuit board from its retaining fingers....and turn it over. I did have a go at removing it completely but the effort put a lot of stress on the soldered connections that would have came out along with the Darlington pairs and heat sink....so as I didn't need to I left it in place, this is what was hiding underneath....
The emitter current pot which should be 100 ohms had been replaced with a 220 ohm component, the resistor soldered onto the back of the board was also 220 ohms....giving a weird sort of 100 ohm result, thing is the wiper will only be tracking across one side....and at best it was increased to 110 ohms, I'm not sure how all this will have been working out...but it now has a 100 ohm 25 turn pot along with the emitter current pot, and its mostly back together without misshap…..
Sorry...along with the "offset output pot"
Replaced the control panel and all the plug in connectors......hooked up my multimeter, poured a glass of wine and powered up......the new pot enabled a very smooth adjustment to 17.9mV. Now it only remains to finish the glass and sit back with a little Crosby Stills Nash and Young
Craig: This all gave enough play to unclip the circuit board from its retaining fingers....and turn it over. I did have a go at removing it completely but the effort put a lot of stress on the soldered connections that would have came out along with the Darlington pairs and heat sink....so as I didn't need to I left it in place, this is what was hiding underneath....
This is how the service manual describes removing the left channel Beomaster 8000 output amplifier. I have been adjusting my technique for some time and I think I have gotten it down pretty good now (for both removal and reinstallation). I like having the output amplifier assembly alone, outside the cabinet to work on and test it. I feel I get more thorough and reliable results that way. There is a better sequence of photos that show maneuvering the output amplifier assembly in and out of the cabinet about halfway down in this post. On a couple of my early Beomaster 8000 renovations I used to remove the components from the heatsink assembly, then reattach them with the board back in the cabinet. Either way it is a pain. One time I even desoldered and resoldered the heatsink component wiring on the circuit board to get the circuit board out. The service manual method is the best way I believe. Especially since I now do all of my no-load current and DC offset adjustments outside the Beomaster. Once everything is tested nothing is disconnected for re-installation.
After a good restoration and adjustment the Beomaster 8000 should run nice and cool for normal listening and only getting a little warm when operated at full output. -sonavor
Sonavor
Thank you....those are tremendous threads, I looked on Beolovers blogs and didn't see those. So helpful and informative, I will be going after the right channel today...don't see any profit in revisiting the left as there only remains to adjust the offset....but I will remove the right side.
Craig
The right channel output board exposed.....looks like the same work has been done to this side.
I haven't seen dust that thick on one of these before.
-sonavor
The emitter current setting is a little high but nowhere near that of the left channel...….
The power supply and remote receiver come out easily enough...….
Right output board and heat sink are a lot easier to remove than the Left....or maybe I'm a little more confident having read Sonavors Thread
This wasn't helped by the fact that the speaker socket had been repaired using epoxy resin, making it a permanent fixture of the housing, bit of manoeuvring got it out however.
Nice work as always.A pleasure to follow.
In most cases when replacing components on the amplifier boards, you don't have to touch the cooling fins.There are stands provided in the Beomasters bottom to keep the board standing up, solder side facing forward, and the leads out the back are just long enough.
Martin
Thank you for the encouragement....always a pleasure to receive, and of course looking inside the case I can now see the two slots designed to do exactly as you say.....I completely missed those. I still have a couple of caps to replace on the left channel so will use the slots on that side when I go back in, meanwhile I'm awaiting some components to be delivered so will concentrate on a bit of cleaning...as can be seen there's a bit to do.
Moving on a little......right output amp complete, looks a lot happier now.
And the power supply and remote receiver complete...….
Reservoir caps of course are going to pose a challenge, Rudy provides a set of sleeves to overcome this issue however he's traveling the world right now until 10th May....at which point I will be off to Greece windsurfing and taking some sun and wine....I do have a plan which involves small sections of UPVC 40mm OD 16bar pipe....
Pre Amplifier next up.....some one has been here already and replaced a cap....
Looking underneath a repair to the track beneath the new capacitor can be seen
More of a concern is the bite someone has taken from what I think is C229 a 220pf capacitor....I know people say these can take a lot of stick and still function....but this looks a bit too much, a replacement will have to be sourced.
Yikes!
I hope you are planning on a nice recapping of these boards. They need it. While doing each board reflow the connector solder joints. On that preamplifier board those six trimmers for the source input levels (PH, TP1 & TP2) are not sealed and can get corroded inside. I try to clean them up with Deoxit and work each trimmer a bunch to clean them up. Once in a while you will come across one that is just a bad actor. There are replacements still available for those and the replacements work with the knobs from the original ones.
The old caps will certainly be headed for the waste disposal...….made a start on the reservoir caps this morning, acquired a length of 40mm pipe and a length of 32mm pipe.....cut to size the 32mm fits nicely inside the 40mm.....new caps have an outside diameter of 36mm, just right for the 40mm pipe ID.
slightly longer than the original....but can be cut back if required......
Right side installed....I don't like replacing these big caps, always too many wires for the posts to accommodate, finished off with some heat shrink sleeve
Yes, these reservoir capacitor replacements on the Beomaster 8000 are always a pain but you did a good job solving it. I like that you installed some attachment terminals on the new capacitor posts before installing them.