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
My Beocenter 1800 seems to be working fine apart from a very low output on the right hand channel. It's not completely dead but the audio is quite faint and much reduced, compared to the left channel.
I'm looking for some advice on what to check. The output transistors seem to read okay, with voltages the same on the faulty channel as the fully working channel. I'm also fairly certain that there are no dry joints either. There is some evidence of a new capacitor having been fitted, probably some time ago, on the PCB that holds the rear heat sink.
To give some background on this, this fault hasn't just occurred. The unit has been stored unused for a while and the fault was there already. So I haven't used it at all but I'm now keen to get it back up and running.
Thanks.
Could be many reasons but the Beocenter 1800 seems particularly prone to kill the signal path series tantal capacitors. I've replaced countless andif one is found bad, you'd better do them all.As said, there could be many other reasons (defective balance or volume potentiometer) , but a scope to the signal path should giveyou an idea where to focus.
Martin
Hello oblongdot. I'm in a similar position and I'm just about to start dismantling the device. Dillen's answer looked good. Did you find the cause and a solution to this ?
OP hasn't visited this forum since then and I never heard back from him.
Thanks Martin I'll proceed as is and advise any useful findings
And we're right here, if you need advice or parts.
What are the exact symptoms?Is a channel missing from the turntable?What about the other sources (Tape/FM)?
My issue seems to be no sound on the left channel from the record deck.
I can do some basic testing using my separate amp (Harman Kardon) controls :
- volume
- balance
- stereo/mono switch
A) If I select STEREO, the left channel problem is evident. More volume does NOT indicate some small signal that can be amplified, it just doesn't seem to be there. Adjusting balance fully to the left produces NO sound
B) If I select MONO, the left channel problem then disappears. Volume works as expected. Adjusting balance to the left produces sound to the left speaker and vica verca.
C) If I select a completely different source, Radio/Tape etc, then all the functions on the AMP side work as expected
I've just realised and do apologise: Beocentre 1800 is not the same thing as Beogram 1800 turn table. Can we move this thread ?
If you have a Beogram 1800 with one of the MMC1-5 range cartridges, it could be a bad cartridge (broken internal coil connection).That's not too uncommon.
Put the deck in play mode (to eliminate the muting shorts) without the cartridge and put an ohmmeter to the signalpath, from the cartridge socket to the amplifier plug.
Martin, I see your logic, thanks.
GOOD NEWS
After doing your tests, I believe the problem has been corrected. In short, I suspect some dirt had got into the cartridge socket and this has now been dislodged.
The process was interesting however as it confounded my expectations. Perhaps I'm still incorrect but it may be useful for others for me to document the process I went through here.
FIRST
I thought that connecting the ohmmeter between the cartridge sockets and the amplifier plug side would show :
- low resistance for R(cartridge) to R(amp plug) for example
- infinite resistance for R(cartridge) to LG/RG/L(amp plug)
However, I saw that the resistance was apparently the same in each case, approx 2 Ohms
The only explanation I could come up with is that the copper like wires from all elements of the cartridge actually act as a single conductor, certainly at the level of fidelity of my meter. Then it's the amplifier's job to detect the very small AC signals on each of the individual wires and possibly eliminate any cross talk etc.
Either way, the expected exception, was of course the L(cartridge) to L/LG/RG/R(amp plug) tests which all showed infinite resistance.
SECOND
After testing and re-testing, I then get the second surprise result. The, L(cartridge) to L/LG/RG/R(amp plug) tests all showed the same result as the R(cartridge) tests. I short, the dirt in the cartridge has been cleared.
THIRD
Testing the record deck to the Harmon Kardon amp then produced all the right results. L and R channels both clear and balance control working fine.
Note I actually connected to the L/LR/RG/R solder lugs on the muting circuit. It was too tricky for me to set up a test system to the amp plug pins per se.
FINALLY
I do seem to have a slow motor problem and will check the other forum pages for this. Do you have any links to advice on motor maintenance ?Suspect graphite grease might be better than oil if the bearings actually need lubrication.
I also see that the BEOGRAM PDF section 5-1 shows how to use the variable resistors for fine tuning.
Can you tell us the 4-digit type number found on the serialnumber label?
5811
Speed settings are accessible from underneath the Beogram, right side near the front.Place the Beogram with the front right corner sticking out over the table edge, you can then go up from below using a 2mm wide flatbladed screwdriver and set the speeds.
Graphite what? No.It's sinter bronze bearings, so a suitable oil will have to be pressed into the material, but the speed is servo controlled, so I would check the settings mentioned above before suspecting anything else.
Much obliged. That's sorted the speed out.
In the process of investigation, I believe I've slightly stretched the turntable belt. Are you able to supply another ?
Yes, I have correct belts for most of the older models.Email or PM me.
New belt has resulted in a vast improvement in turntable. It was approx 1.5inches shorter and still rubbery unlike the old dried out one.
Unfortunately, the improved performance from the cartridge / socket / arm / wire assembly hasn't lasted. It may well be dirt or some other problem, not sure, it did disappear once more with some very fine wire poking but that was short lived....... Overall it seems unlikely to me it's an electrical component problem on one of the circuit boards I may be wrong.
Obviously not keen on replacing the entire arm even if available, would you be able to advise on any further lines of investigation / options here ?
The most likely culprit in cases of a missing channel is the cartridge itself (broken coil connection inside the cartridge).I take it we can rule that out here.
Next: Broken signal leads. Also quite common.In decks with RCA plugs they break unnoticed INSIDE the pvc sheathing, apprx 1-2cm outside of the RCA plugs. A wiggle here can sometimes confirm the diagnose. Remedy is to short the cables by 5-8cm and fit new RCA plugs (or fit a new cable altogether).In decks with a DIN plug, the leads break off inside the plug where they are soldered to the plug pins.
Last, broken tonearm wires. They typically break off at the back of the cartridge socket or just a milimeter or two from there.It's rare, but it does happen.
There are no electronics in the signal path in these decks, so the above is pretty much what can go wrong.
That's good stuff. It surely must be broken tonearm wires. The cartridge socket is still responding to pokes with a thin wire.
Are there any options for replacing these wires ?
Hello Martin, just wanted to follow up on your earlier advice: are there any options for replacing the tone arm wires or is a whole arm assembly that's likely required ?
It's possible - but not particularly easy - to replace the thin wires.
Have you diagnosed the problem to be inside the tonearm?
I believe so yes. The DIN plug seems fine. Wiggles of the cartridge and especially a gentle prod into the socket of the dodgy channel can produce a temporary resolution
And t's not a fault in the cartridge?That's about as common as faults inside the tonearm.
No I don't think it is the cartridge. In some ways I wish it was. Earlier tests connecting from the L(cartridge) socket to L;LG;RG;R muting circuit wires all showed infinite resistance. Originally I thought this was due to dirt, but jiggling it seems to temporarily solve the problem - resistance wise and channel wise. That it comes back seems to suggest the work of gravity and vibration in the arm.
Is there a way of testing the cartridge that's exclusive to the tonearm wire scenario ?
Often, the cartridge socket will come out of the tonearm tube when dipped into boiling water and then pulled carefully and gently.It may take a couple of dips - and make sure the wires are free to move at the other end.
You can check the cartridge coils with an ohmmeter.
BEOGRAM 1800 record deck / removing the cartridge socket from the tonearm tube ...
The time has finally come for me to try the boiling water process you previously kindly suggested.
The signal has now failed on both R and L channels.
Two silly questions if you able to give some further help :
- did you remove the entire tonearm before dipping the end in water or is it a matter of rotating the entire deck with it still attached ? Do-able if unexpected.
If this all looks too much, I was wondering if a hair dryer might do the trick but probably not hot enough.
many thanks in anticipation