Beogram 4002 arm no longer lowers

[david winter]

Hi,

I've been working on a 4002 type 5511 which played records fine until the arm lowering stoped.
Since, the Up/Down button no longer acts on the arm.
The main board is recaped, trimmers replaced, carbon resistors checked etc. I have 20.8V after 1IC1.
While checking the arm switches, I noticed that if I very quickly pushed the arm's "end of return" switch, the arm would sometimes lower.
In this case, pressing the Up/Down button will lift it, but the arm won't lower.
As the issue is clearly not on the keyboard side, it's somewhere in the circuit which enables the solenoid when the pulse is detected, but probably not in the part which disables the solenoid.
Any hint appreciated. Thanks.

 

[big2bird]

Is it "clicking" the command or not? The audible click they make.

 

[david winter]

You mean the click the solenoid does when energized ? No. Pressing the button doesn’t produce any click (except when doing the trick with the end-of-return switch).

 

[big2bird]

Sounds like it could be the photocell/lamp source detection circuit.

 

[david winter]

I replaced the lamp (OIL1) by a bright LED. The photocell outputs up to 200mV when light reflects properly.
Else I'll need to know the characteristics of the original light bulb.
Also, the arm lowers and lifts without trouble when removing 1TR6 (which tests good in my DCA75).

 

[big2bird]

I am out of ideas. Removing 1TR6 enables solenoid is a mystery.

 

[david winter]

Removing 1TR6 does not enable the solenoid, but causes the Up/Down key to lower/lift the arm.
Something drives TR6 such that the Up/Down key presses are ignored.

 

[big2bird]

The solenoid is what actuates the up/down motion, so Im lost.

 

[david winter]

Of course, but the problem is in the sensor signal circuit, which enables or disables the Up/Down key.
Luckily I disoldered one leg of the 1C2 cap to measure the DC offset without the photocell voltage applied, and measured 3.3V, a bit low.
After soldering the leg back, the problem disappeared.
As I did all solders sometime ago, I can only think that the problem was due to a weak contact with the leg, or some invisible cold joint under the shiny solder. Or maybe an intermittent contact in the cap (I've seen this one with a NOS cap a long time ago).
I contacted BeoLover who very kindly helped and gave helpful hints.

 

[big2bird]

Very good. Be sure to clean and lube that solenoid plunger.

 

[david winter]

Of course, I did that in the begining.