My Beomaster 2200 with Beogram 3000 has horrible sound quality on phono. Treble sounds rough, bass is distorted and choppy and the volume is low (needs to be at 8 to be reasonably audible but previously 3 was fine). On FM the sound quality is perfect so I suspect the phono preamp. If anyone can shed light on where to look for this fault I would be very appreciative. Thanks  

The service manual is on site. However check the record player first - more likely the stylus is shot than anything. If it plays well though another amplifier, the BM2200 service manual is on site but you will need to be a silver member to access it and be competent with circuit diagrams and have the right equipment!

I agree with Peter, the cartridge could be the sole reason.

Having said that, the phono input is the most sensitive in the Beomaster, so is
usually the first to be affected by f.e. an unstable power supply.
I would grab a capacitor kit and replace the lot. Aging caps are the cause
for the majority of faults in these wonderful machines.
I'm sure that, if the caps in your Beomaster hasn't been renewed yet, the ones
on the power supply module (at the bottom center of the Beomaster) will be
visibly cracked. Probably others as well. Those red cylindrical ones are horrible.
Replacing caps is a job for a person with electronic knowledge and soldering skills.

If you take the Beomaster apart, note the little spring for the aluminum lid. It sits on
the horizontal black rear metal plate under the black top aluminum cover.
Of course, it would be worth upgrading your membership and get the whole servicemanual.

Martin

Thanks Martin, I have the original documentation for the BM2200 which includes good circuit diagrams - will the service manual offer much additional information?. In a previous life I was a computer engineer so I'm comfortable with electronics (less so with analogue!) and soldering etc.

I notice the 35V supply to the phono circuit is down to 32.4V but I haven't yet had time to trace much further. You mention a capacitor kit - do you know of a stockist who has a kit for this machine?

Thanks to you and Peter for your help.

Gordon 

Gordon,

The voltage is not the huge problem, it's essential that it's clean and free from ripple and noise.

You have a message regarding capacitor kit, check your inbox in the top right corner.

Martin

Thanks Martin. I have now replaced all of the electrolytic caps and noticed C3 in the power supply had been leaking so I thought I had found the culprit but unfortunately the problem remains.

I have also just repaired my Tektronix 465 oscilloscope wich I haven't used for about 5 years (also a cap problem!) so now I can monitor the BM2200 properly.

I see about 50mV of quite noisy ripple on the +35V supply line and the waveform looks sawtooth. Is that what you'd expect? 

Good job on the caps. Now we know that that part is alright.

The amount of ripple is no problem. The sawtooth waveform is to be expected and not a problem either.
You will have to connect a signal generator to the phono input (or play a test-record on a turntable) and use the scope
to find where the signal gets distorted.

Martin

Thanks Martin. Whilst I'm waiting trying to find a test record, I measured around the power supply and here's what I found, I'd be grateful for your comments:

P31-1, -31.53V, 250mVpp sawtooth ripple

P31-2, +31.15V, 580mVpp sawtooth ripple (note I swapped over 5000UF caps and this stayed on the +30 supply)

P31-3, +33.0V, 50mVpp noisy ripple

P31-4, +14.8V, 20mVpp noisy ripple

P31-5, 6.21V, 1Vpp 50Hz sine wave

P31-6, 21.8mV

P31-7, -26.3mV

P31-8, GND

P31-9, GND

With the new caps installed, if the problem is limited to the phono input, I think we
can rule out the power supply.

Did you try using a different needle/cartridge or turntable ?

You could also check inside the DIN plug on the turntable signal cable. Especially the ground connections.

Martin

Thanks Martin

Unfortunately I don't have access to another turntable or cartridge so I'm just going to have to try to debug this the hard way. I have been in touch with the previous owner of the 3000 who is very trustworthy and says the turntable and cartridge are both good. Unfortunately, he now lives about 500 miles away so I can't use his components to isolate/test.

I'm trying to find a test record so I can check the path from the stylus all the way through the phono amp. 

A test record can be expensive to find but the correct way to go.
In the mean time, open the DIN plug and check the solder joints inside. Especially the ground connections.

Martin

Thanks. I opened the DIN plug and the connections looked OK - no sign of solder splashes or flux. I re-soldered anyway but it made no difference. I also tried with/without the ground wire on the DIN shell. I ran a separate ground wire between turntable and amp but no change either.

I will be getting an old B&O system to play with in the next few days so that may assist fault isolation. Don't know which model yet. 

So now I also have a Beocentre 7000 with working turntable and good sound on S-45 speakers to continue the faultfinding. The cassette deck is not working but I'll look into that later. My plan is to rig a connection from the 3000 DIN plug into the phono preamp board input on the 7000 so that I can verify that the 3000 and its MMC4 are OK. I'll post the results when that's done.  

If you have already replaced the caps, take a good look at the resistors.

I recently had a BM1600 come in for repair, where I had to replace all the resistors in the signal path. All of the resistors were out of spec by at least 10%, and a couple were out by 80%. That was after I'd already replaced all the caps.

Those old carbon resistors do not hold their stability as the years go on.

I used Vishay Dale CMF55 and CMF60 to replace them.

Menahem

Problem solved! I rigged a  temporary cable from the Beocentre 7000 cartridge output to the DIN phono input on the BM2200 and got good sound on both channels confirming the 2200 was OK. I then traced the problem on the 3000 to a dry joint on the signal cable ground connection at the small pcb inside the turntable.

So in summary, my problem was a poor phono signal from the 3000 turntable but it was definitely worthwhile replacing the caps in the BM2200 since I found one cracked and another leaking.

Grateful thanks to all for your help.

PS The Beocentre 7000 I have recently acquired has a problem with the tape drive and also the tone arm returning but not lifting off the record when pressing STOP. I will open a separate post for this once I have cleaned the unit up and made some checks.

Thanks again. 

Hi Pete

Tape deck issues will usually be:

No tape playback - broken belts, see member Dillen (named Martin) for replacement belt kit.

No fast forward but okay rewind and playback - this means the jockey wheel which controls fast forward has sized, it needs relubricating.

I recently fixed both issues on my BC5000, see my post here for details:

http://forum.beoworld.org/forums/t/25412.aspx  filed under Beocenter 5000 cassette deck in Workbench.

In addition, I believe your turntable issues can be either 1 of 2 things:

1. there is a small grub screw on the arm used for controlling lift height, its up the back of the arm, check for missing screws or incorrectly adjusted - service manual provides this info and is available on this site

2. I think there is some fluid used to dampen the movement of the tonearm, this may have dried up or leaked out and might need replacing, you can search on this site for that info. Note the Beocenter 7000 7002 and 7007 are essentially the same units in terms of mechanics (save some minor differences in the TT arm) so you can search for problems, most people around here have the 7 series units, not the 5000 such as you and I have.

Hope this helps,

Andrew

Thanks Andrew

Careful cleaning and a tiny amount of sewing machine oil fixed both tape drive and turntable. Everything works fine now.

By the way, does anyone know what the sticky material is that is used on the plastic linkage to damp the top cover movement on the BM2200?

Yes, it's kilopoise grease. (The prefix kilo- here suggesting a very low grade of viscosity).
Don't use automotive grease, most types will attack the (oil-rich) plastic !

Martin