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, there was another member that had the same problem as this, and it was corrected with the adjustment of the detector lamp.
unfortunately, this does not fix my problem.
i attempted a lot of diagnosis, and I am currently at a loss.
i have disconnected the detector, to make sure it’s not causing the problem. And it’s not..
‘I have replaced all the tantalum caps (There were quite a few out of spec, so did them all).
i can make this behaviour go away (as in the tonearm goes all the way across), if I disconnect the sensor lamp (whether the detector is connected or not). Obviously you need this lamp connected to get the right voltages around tr5 and 6.
all the voltages around Tr5 and 6 measure correctly.. not sure what else could cause this behaviour.
is there any other path in the schematic that can cause this travel to stop at 12” marker?/
The tonearm will be lowered, if the sensor doesn't see the platters radial streaks.Hover the sensorarm above the rotating platter. Put a scope to the output from the opto cell in the sensorarm andarrange the sensor arm lamp to give the best possible signal (highest pulse amplitude).Still no luck even with good pulses - work your way through the filtering etc. to see where the sensor signal gets lost.If you have an anti-static mat or similar on the platter, the deck will think it's a record.
NEVER use antistatic mats with Beograms.They are not necessary and they will cause a wrong needle tracking angle.
The sensorarm height above the platter (lens focus point) is also important. The light spot on the platter must be fairly clearly defined.
Martin
There is no platter mounted... therefore it should not stop.. but it does.
‘That’s the problem..I need to fix that first before I go down the path of the detector itself.
something is telling the circuit that there is a valid record underneath it.
And I have disconnected the detector. If all was good, it should not stop with the detector disconnected?
No platter = no streaks passing by under the sensor = no pulses from the sensor = Beogram thinks there is a record.
No sensor = no pulses from the sensor = Beogram thinks there is a record.
All normal!
Try with the platter and belt etc. all fitted.
Let me start by thanking you for that description.. it works as you have now described.
my previous 4002 didn’t work like that, but still behaved correctly when the platter was on and rotating.
that one, when the platter was removed, would not stop at all, unless the beam was broken, by hand.. naturally, I thought all 4002 worked that way..
‘all good in the end. Many thanks.