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
I have had this unit for years but don't know how long I have had the fault as I usually have a record on the platter, so no problem.
However, after moving house, I noticed..
Press "Start" with no record on the platter, it goes to the 30cm position and sets down. Press start again; the arm lifts, goes to the end, changing to 45 RPM at the right place without setting down, then gracefully returns and switches off.
With a 17 cm record on the platter and repeating the process, the same thing happens (it does not set down at 17cm)
Where should I start to look to fix this?
Thank you.
Welcome to Beoworld!By now most of these decks will be found in need of a more thorough restoration rather than discrete repairs.Is the sensorarm lamp lit?Check the output from the sensorarm, on the scope you should be able to see the pattern from theradial streaks on the platter as it rotates while the sensorarm hovers above it.Martin
Hi Thanks for the reply.
I don't have a scope. Is there anything else I can do? The sensor arm is lit with the red B&O and I can see the 'image' on the platter but of course that is no guarantee of an output.
I tried "start"ing repeatedly to confirm what is going on and occasionally (1/10) it will work properly if that offers any clue.
Thank you
Decreased lamp light output (degraded lamp)Wrong placement of lamp in relation to the lens system.Bad filtering of the sensor output signal.
Martin
Edit:Third attempt at posting this message.
I'll investigate when time allows and report back..
I am pleased to say after cleaning the lens under the detector arm with a spectacle cloth, the machine is back to working order.
Thank you for pointing me in the right direction.
Well a couple of years on and the same fault has occurred except the arm always lowers when no record is present.
I believe one of the pots on the board changes the sensitivity of the detector arm? Before I start changing other things I would like to try that. But which pot is the correct one to alter? The board I have is in the attached photo. I have tried altering the position of the bulb in the detector arm - no difference
Thanks Peter
I think the pot your thinking of was fitted to allow the playing of semi transparent albums which came into fashion at one point, dont think I have ever seen one, the pot was to reduce the sensitivity of the detector so it would ignore the partially visible ribs of the platter that could be seen through the semi transparent album. Your problem seems more like the detector is already ignoring the ribs. I would be more inclined to suspect the photocell....to be sure you need a scope to take measurements, and the circuit diagram along with some confidence to have a go....
Craig
It might be an obvious question but is your belt OK and in good condition?
As the belts age and stretch, the turntable can take longer to spin up to speed. If it's not spinning fast enough by the time the sensor arm reaches the platter edge, this can be fooled into thinking that one of the black ribs passing by too slowly is actually a record, so the arm drops.
AdamS
Thats a very good question actually ;¬)
It drops even if there is no turntable present. I took the turntable off to take the board out to photograph it, testing before I did so. I too think it might be the photocell. Is there a continuity test that can be done? If so, what reading should I get? I don't have an oscilloscope but may see if my meter can detect low AC
It would be nice to know what the other 3 pots do (and which is which) The manuals I have don't refer to that board. I believe 2 are for forward and reverse speed.
Thanks
Thinking about the information you gave an changing the capacitors, I have tested again withthe turntable in place and it works! Clearly one of the capacitors was faulty, plus I misunderstood that the the deck needs to 'see' the stripes in order not to drop.
Thank you all again for your help. The old girl is up and running again.
As an aside, reading another thread about balancing the tonearm, I can confirm the weight adjustment knob does get stuck and needs to be freed up in order to be able to set the arm to floating weight without fouling the arm.