Building a VU meter for you multimedia PC

Step 2 Repairing and preparing the vu meter

First of all you need to find out if the vu meter works. Therefore you need to have 3 voltages. +15V, -15V and +5V. I did some research on the connections but I could not find out about every connector on the board. The function of some pins are still unknown to me.

XS1 (Analog)

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1 - Analog in right channel
2 - Analog in left channel
3 - Up/Down Counter Select (open=down, +15V=up)
4 - GND
5 - nc
6 - VCC (+15V)
7 - GND
8 - nc
9 - VDD (-15V)
10 - Heater 6.3V ac
11 - Heater 6.3V ac

- 8 is not connected. It is marked as 22V but not used. Maybe this comes from an old release of the pcb
- 10 and 11 are the heater connection. I used 5V dc here and it works very well.

XS2 (Counter)

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1 - ?
2 - Discharge (open=count, +15V=counter reset)
3 - ?
4 - nc
5 - Count (Count +15V pulses)
6 - GND

Take a FET transistor like the BF256C or the BF245. The FET is not really critical, because it is needed as a constant current source with rather low current. Solder the transistor onto the pcb. You need to cross the D and S pin to make the fet fit into the holes.

Now you can test the device, if you got a power supply.
You need to put some capacitors into the audio channels because the input of the vu-meter is dc coupled and you amplifier may not like this.

To Test the device you should turn the turn R16 and see if you can adjust the zero point. Every dot but the first one should disappear when the display is adjusted. The first dot is lit permanent.

Next you should power up the music. Use R5 and R6 to find out if the display can be adjusted to show all dots.

If the device is working well and you are satisfied with the brightness you can do the next steps. If it is defect or it looks ugly, take another one and test repeat the tests.

Now you need to prepare the display. The way it is mounted it is a little bit to high to fit into a 5 1/4 case.
You need to cut the pins on the top that are left from production. Then you need to desolder the display and bend the pins 90 degrees to the back of the display. Be VERY, VERY careful doing this! If you aret to forceful the glass of the display could break. If that happens, take another display from another board and try again.
Now solder the display the display back to the pcb, directly on the soldering side. You need to put a plastic strip between the display pins and the pcb.

Remove R1, R2 and VD8 from the pcb. They are not needed when using 5V to power the heater. If you do not remove these parts they will melt, be warned ... :-)

Now the display is ready for mounting and you can concentrate on the psu.