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
Hi everyone.
As I mentioned in another thread, one of my acquaintances has a BeoMaster 5500 and a MCP5500 that are acting up a bit, so he asked me, if I wanted to take a look at it. I told him about the usual problems with dried out electrolytic caps and bad trimmers, so we agreed that it was probably best to give it a complete overhaul.
He had told me, that there was a humming sound in the speakers and that the BM would turn off by itself quite often. After he had dropped the BM and MCP off at my place, I hooked a pair of speakers up to the BM and fired it up. There was clearly some humming, and it sounded like the humming from the BM was being amplified through the speakers. I unplugged the speakers to listen to the BM, and it was indeed humming by itself. I turned the BM off again and unplugged it from the mains. It was here I realised how hot the heatsink had gotten. I only had the BM turned on for a couple of minutes, but the heatsink was very hot, so something was clearly wrong!
I had made some initial research on the BM5500, and at some point I found this page on Beocentral describing that high frequency noise in the preamplifier could make the power amplifier overheat badly, so that was definitely something I wanted to look at, as I had a feeling the overheating wasn’t just caused by a pair of trimmers that had gone out of spec.
I got the BM on the workbench today to make some measurements and tests to give me an idea of what was going on. I took the cover off first, as I wanted to measure the idle current. I noticed that the screws for the tuner board were loose, so it could seem someone has been in here before.
I slowly increased the voltage on the variac until it reached 220V. Everything was looking fine, so I turned the BM on. Idle current and power consumption raised quite a bit, but since the idle current must be measured with the volume at 00, I turned it down to that. With the volume at 00 the I got a measuring of 21 mV between TP200 and TP201, which is 10mV more than specified which isn't all too bad.
Power consumption at this point was 220V x 0.17A ~ 40W. Heatsink was staying cold.
I then increased the volume to 02 which more than doubled the power consumption (220V x 0.42A ~ 90W)!
I then looked at the idle current. I had to press the '1000' button to get a useful reading. The idle current had tenfolded so it was 200mV now!
The heatsink was getting hot quite fast when the volume was more than 00. I noticed a strange thing when playing with the volume. At 08 it would use 120W but at 10 it would drop to 80W. This was in fact the case for the whole volume scale; power consumption would increase and then drop again for every few steps. I could hear a slight change in the hum when the power consumption dropped. I turned the BM off again and cut the power.
Next step was to try with 3P22 disconnected. Power consumption dropped to 35W with that disconnected and idle current was measured to 18mV. Naturally changing the volume wouldn't change anything now, as the power amp wasn't getting any signal from the preamp.
Since the power amp seems to be OK, the next step will be to see, if adding a 100nF 63V cap to the B-E junction of 2TR8 as described on Beocentral will cure this problem.
/Dennis
Dennis:With the volume at 00 the I got a measuring of 21 mV between TP200 and TP201, which is 10mV more than specified which isn't all too bad.
It's more than double the specified value. I'd suggest you rectify that before adding extra caps anywhere.
--mika
The 10 extra mV across the two emitter resistors clearly isn't the source of the overheating problem as I ruled that out by disconnecting 3P22. The heatsink was cold as long as the volume was at zero with 3P22 connected and all the time with it disconnected. Besides that, Martin wrote here that he sets the idle current to 8mV across one of the emitter resistors, so it really isn't that far off.
The Beocentral page was actually linked from a blog owned by a Danish guy who also repairs old B&O equipment, and he had the same problem with a BM5500 and solved it by adding the 100nF cap, so I think it's a general BM5500 problem.
More will come when I've ruled out the overheating problem. If adding the 100nF cap doesn't solve the problem, I'll have to dig out my dads old oscilloscope from the back of closet.
Double post.
Replace the small (10uF and 22uF) caps near the voltage regulators.They lose their filter properties, introducing noise on the voltage rails to the preamplfier.In severe cases the noise is easily audible, often "digital"-sounding and changing in characterdepending on the volume and tonecontrol setting (and at a volume unrelated to the volume setting).
Martin
@Martin; Thanks, will change them first then when I get back to it later this evening. Do you think, that it would be a good idea still to add the 100nF like the four 220nF capacitors C215, C216, C415 and C416 were added by B&O to stabilize the power amp? And do you know, if there were made other corrections in the circuits during production?
I almost have all parts needed for this project now. I have chosen to use the following caps for this project:
- Radial electrolytic caps over and including 4.7uF will be replaced with Panasonic FC-series except for the big reservoir caps which will be replaced by a pair of Nichicon GU-series.
- Lower value radial electrolytic caps will be replaced by WIMA MKS2 film caps.
- The axial electrolytic caps will be replaced with Nichicon VX-series except for C6 on the fan regulation board, as I couldn’t find that value in the VX-series. I will use a Vishay for that instead.
Besides that I will change the backup battery, the mute relay and the trimmers for the idle current where I will use Piher PT10s. Most of the parts have been bought at Mouser. I have saved the BM5500 as a project there, so if someone wants to use the same parts, I can send you the list. Mouser can’t deliver 1uF 50V WIMAs before April though and the 2.2uF 63V WIMAs I had bought turned out to be too big to fit on the boards, so I bought some 1uF and 2.2uF 50V WIMAs elsewhere.
B&O added the four polyester caps to prevent self-oscillation.Since this is a Beomaster 5500, I would expect to find them already fitted (though they may not show in the schematics).If not, you could choose to do it - but if the problem relates to the input signal, they will not fix anything and I think I would leave it as-is.
Are the two large cans defective? Are yours the golden or blue type?These are usually in suprisingly fine condition and of a very good quality. I wouldn't replace them unlessI really have to - and in that case I'd gladly fit good used ones from a donor Beomaster.The same goes for the two large ones in Beomaster 6000. I've always found them exceptionally good and they practically only fail ifphysically damaged.Also - what made you choose FC, VX and GU series?
Yes, the 4 220nFs are there - C215 and C415 seem to be different though as seen on the picture below... And they didn't spare on the thermal paste!
I think I'll try to see first, if the 100nF fixes the problem and then maybe leave it there if it does to prevent it from happening again in the future. They new electrolytics will age as well as the old ones - the 100nF won't.
According to the owner, the BM has turned off by itself quite a lot of times, and I can only imagine that was due to overheating, so the two large cans will probably have seen quite a lot of heat, which is why I've decided to change them. And besides that they are 30 years old after all.
Regarding choice of caps; I wanted caps from reputable brands and other people seems to have had good experience with those.
You didn't tell me, if those "bad, ancient, well-cooked and heavily overdue" large cans are golden or blue?
@Martin; Golden Roederstein as seen on the picture below.
I got board 2 (output and powersupply) out of the BM.
I considered mounting the 100nF cap on the underside of the board, but following the traces I could see, that it was also possible to mount it in the holes of J36 and R16 as shown on the picture below and thereby get it on the component side instead.
Here's how it looks mounted in place:
So, I got the board back in the BM for a test. I was very pleased to see, that the idle current and power consumption would now stay at the same level no matter how far I turned up the volume and the hum is gone as well. Will try it with a pair of speakers tomorrow as it's getting late now. A thank you to the guys at Beocentral is in order!
Next step will be to recap the board and get the trimmers replaced and idle current adjusted.
Got a little further yesterday. Started off by playing some music at mid to high volume though a pair of MC120.2 for about 15 minutes. Heatsink only got lukewarm, so that was a good sign compared to how it looked when I first got it. After that I pulled board 2 out again to get started on the recapping. Here it is with the new components next to it:
And this is how far I had gotten as I called it a day:
:
I still need to replace the 3 largest caps, so that'll probably be the next step. I received the new muting relay today, so I can get started on board 3 (preamplifier) once I've installed board 2 again and had it powered up to make sure everything still is as it should and to get the idle current adjusted. Only parts missing now for this project is the 33uF axial cap and backup battery.
Got board 2 back in the BM this weekend and adjusted the idle current. I had set the new trimmers to roughly the same position as the old ones when installing them and the idle current was only of by about 2 mV in each channel as I powered it up. Adjusted it to 11mV for now. Will measure it again later and will probably also have to adjust it again, as I'm thinking of rewiring the transformer to 240V instead of 220V as we have 230V here in Denmark.
Board 3 (preamplifier) is coming along as well.
Got most of the caps replaced. 16 of them are 1uFs, which are replaced by WIMA film caps - using WIMAs for the 2.2uFs and the 0.47uF as well.
Will continue with board 3 tomorrow.
Only need to replace the 2.2uFs on board 3 now. The reason why I haven't replaced them yet is that my wire cutter is to big to access the legs, so I've ordered some different ones that hopefully will be able to get in there.The copper traces on these kinds of boards lift quite easily if one isn't careful, so I prefer to cut one of the legs on the old caps on the component side so they just fall out when desoldering. Beware that bending the caps to gain access to the legs should be avoided, as it could lift the traces as well. If the new wire cutters are to big, I'm sure my old man has one that will do the trick.
Do you remove components by bending and pulling them while heating the joints?Yes, that WILL destroy the board.Instead, remove the solder and then pull out the component.No cutting.This way the board will not suffer (and neither will the component, which is important if it is to be reused).And if the copper traces lift when you work on the board, your soldering iron is far too hot.Around 280 degC is usually fine for this type of board.
I actually believe I wrote the opposite...
I cut one leg of the components (if they are to be scrapped anyway if that isn't obvious...), so they just fall out by themselves when removing the solder - I'm not even touching the components if I can avoid it cause if there is just a little bit of unmelted solder left between the component and the trace, you can be almost certiain, that the trace will lift. And since I don't have a fancy desoldering gun with vacuum but mostly use desoldering braid, I find this the best way to do it.
Oh yes, I read it different now...;-)
Received my new tools - two cutters and two pliers! The total price for the 4 was £35, but that was by using a £5 voucher - normal price is around £10 each.
That meant I was able to finish up the preamplifier. Got it back in the BM5500 this evening and enjoyed some music afterwards. Source was mainly Spotify through my iPhone, so not the greatest. I'm exited to get a proper source connected - could be fun to compare it to my unrestored BM5500 as well!
Plan is to get the tuner done tomorrow, convert it to 240V followed by another idle current adjustment and then a proper listen!
Managed to get the tuner board recapped today!
Back in place.
Decided to rewire it to 240V before powering it up again. Replaced the 1000uF axial cap at the same time.
Took it into my room and hooked my MS150.2s up to it. My first impression was, that it was sounding very crisp and clear which I also had expected. I have been using a refurbished JVC JA-S77 (nice amp btw.) for the past 6 months or so, and compared to that, the BM seemed to sound crisper and have more low end. I turned the volume up a bit and soon noticed, that the BM was very harsh sounding actually. It didn't strike me as that harsh when listening to it though my MC120.2s yesterday, but since I was sitting only 1 meter away from them yesterday naturally they would sound a bit more "in your face". I wondered if the film capacitors could make it sound this way and actually began to consider, if it was a mistake to use them, cause it was very tiring to listen to.
After about 10 minutes I grabbed the MCP5500 to turn off loudness. Hmm.. wonder what the bass setting is set to... Hmm... 3+! What about treble then? Doh! 6+ I usually always have it all at 0 on my own equipment, so I hadn't thought about checking those settings before now. Set it all to 0 but enabled loudness again - muuuuch better! The rest of the house is sleeping now, so will have to wait till tomorrow before I can turn the volume up again, but even at low volume it seems to play as intended now.
Nice clean job Dennis, I had the same experience with my 5000 stack when my son was here last time, I rigged the stack with Bvox 3702 in his room, after he left I played a record, sound way off, and yes full treble and bass, playing loud total distortion in the highs and a boooooming bass, but he played mostly from his Iphone, maybe they need that or young people like it that way, the music he plays sound distorted all over
Collecting Vintage B&O is not a hobby, its a lifestyle.
Thanks Søren!
Well, at just short of 20 years of age, I would describe myself as young, but that kind of sound is definitely not for me! But yes, sadly the majority of the young people don't seem to care much about sound quality...
Was able to turn the volume further up today and it sounds good! And the heat sink doesn't get more than lukewarm even after playing at high volume for a while, so everything seems to be as it should. Getting good radio reception as well.
Display board has been recapped and the IR LEDs cleaned. Gave the backside of the front panel a clean as well.
Only boards left to recap now is the fan regulation board and the microprocessor board - 2 caps on each. Still waiting for the last parts for the microprocessor board to turn up.
As this thread is pretty recent & resplendent with pictures I have some comments & questions. Clearly I am dillusional thinking that I can do these repairs myself. That is my comment. My question is this; does a list of qualified technicians exist, hopefully sorted geographically? I am in Toledo, Ohio and need help. Beomaster 5500, Beogram 5500, Beocord 5500, Beogram CD50, MCP5500, Beocenter 3500 & S45-2 speakers all have some issues. Most have been in storage for a long time & are cosmetically near perfect. But it all functions less than perfect. Thanks for any advice!
Dom
2x BeoSystem 3, BeoSystem 5000, BeoSystem 6500, 2x BeoMaster 7000, 2 pair of BeoLab Penta mk2, AV 7000, Beolab 4000, BeoSound 4000, Playmaker, BeoLab 2500, S-45, S-45.2, RL-140, CX-50, C-75, 3x CX-100, 3x MCL2 link rooms, 3x Beolab 2000, M3, P2, Earset, A8 earphones, A3, 2x 4001 relay, H3, H3 ANC, H6, 2014 Audi S5 with B&O sound, and ambio
Call your nearest B&O store (Cincinnati?) and ask them if there's a local repair facility that you can drive to.
'Hope you have deep pockets.. B&O is expensive to buy and expensive to repair.
Hi Denis,
The trimmers which you used above are those one:
https://pl.mouser.com/ProductDetail/531-PTC10V-100 ? I know the parameters but I cannot check the hole spacing in the PCB, if you remember could you please confirm?
Thanks;