This article, the third in a series about restoring a Beocord 9000’s peak program meters (PPM), focuses on installing and calibrating the rebuilt PPM.

The initial step involved switching the original current limiting resistors with values suitable for modern SMD LEDs. These LEDs are more efficient and brighter, requiring significantly larger resistors to match the original brightness. Testing showed that 470 Ohm and 330 Ohm resistors for red and green LEDs, respectively, produced slightly brighter output compared to the original 180 Ohm and 120 Ohm resistors. This resulted in approximately 10 mA current compared to the original LEDs’ 40 mA, despite the older LEDs having lower intensity.

A photo highlights the original resistor bank (the eight resistors on the left).

The next image displays the newly installed resistors. Although the PPM uses 16 LEDs, it only has eight resistors because the left and right PPMs are multiplexed at 60 Hz, meaning only eight LEDs are active simultaneously. This is evident in the signals of the two common anodes (pins 1 and 2 on the display board) which each power one PPM:

Here’s an image of the installed new resistors:

The rebuilt PPM after installation:

And finally, the PPM in action:

It proved beneficial to fix the display boards sequentially, leaving one installed as a reference point for alignment. Marking the insertion depth of the displays on their headers ensured the correct slant within the plastic bezel.

The next step involves replacing the scale illumination bulb with a red/green SMD LED.