Beogram 8000: Electrical Work Checkout and Forward/Reverse Voltage Adjustment

After testing some basic Beogram 8000 control functions I am satisfied that the electrical work is done. It is time to bundle up the microcomputer board box so I can move on to the service manual adjustments.

The microcomputer box lid contains a heatsink for the processor device. I had cleaned off the old thermal compound and applied new compound.

The lid attached securely and I can peak in the end and see the thermal compound is sandwiched nicely between the heatsink and processor.

While the main Beogram components are still out of the chassis this is a good time to do some of the service manual adjustments. There is still one that is related to possible electrical tasks and that is the adjustment of the forward and reverse voltages for the tangential arm transport.

There is a common lamp with two photo resistors on either side in the Beogram control panel. One photo resistor (R9) is for forward movement and the other (R10) is for reverse movement. The voltages on those two resistors should be 650mV when the Beogram 8000 has been on for at least five minutes and the Play button is activated (with the tangential arm assembly stationary).

I initially measured around 600mV for the reverse photo resistor (P5-6, R10) and 300mV for the forward photo resistor (P5-4, R9). Here are the measurements after the adjustment.

Here is what the related connector, P5 looks like on the Beogram 8000 control panel.

This picture shows the final position of the forward/reverse adjustment screws.

The relative positions are a little unbalanced to say the least. I will recheck those forward/reverse arm motor voltages again before wrapping up this project to verify the settings are stable.

Beogram 4000 Arrives From UK! Solenoid Oscillates!

I just received another Beogram 4000. This time from the UK. The unit is in decent condition, at least it has the MMC cartridge mount intact and the sensor arm insert is still there. The cueing/tonearm lift control panel came loose during transport. A great idea to tape them down. Luckily, the seller had the deck covered with a heavy duty plastic foil under the hood, so nothing bad happened. It will be straight forward to re-attach the panel.

Inside it seems everything is present:

But of course, like most units of this age it passed through some less-inclined hands and suffered a bit. I am not sure what attracts people to cutting off power cords, but this one, like the one I just obtained locally, had its power cord severed. So I bought a power plug and attached it to the cord:

Then it was time to plug it in. The first thing I usually do with a Beogram of unknown provenance, I measure if the voltage rails are present. At C1 one can measure the rectifier output for the 6V rail that drives the control system. It should be somewhere around 12V:

And on C2 one can measure the regulated 6V rail:

This looked pretty reasonable, so I went on to the 24V rail that is responsible for the power side of things. First I went for the rectifier output at C3:

And then for the regulated 24V rail at C4:

This seemed within spec, so these capacitors seem to have some remaining life left in them. I will exchange them anyway, but this was good enough for an initial turn-on of the deck.

I pressed the start button. Happy moment: The strobe lamp still works:

The carriage was also set in motion (good!), but then at the point where the tone arm should have been lowered into the lead-in groove of a 30 cm vinyl, a strange phenomenon occurred: The solenoid emitted a loud noise and its plunger oscillated rapidly. A 2 min video is more than a 1000 words, so I made one! Here it is. It demos the issue and shows how I repaired it.

Essentially, all it took to fix this was to reattach the lead that connects the emitter of TR4 to the current limiting resistor that is on PCB #7:

Let's see what else this Beogram has in storage for the Beolover!