During the restoration of the Pioneer P-D70 I found myself in front of the pcb smeared with a strange tar, at first glance it seemed that someone had accidentally poured it on the board. Instead during the desoldering of the VTF 056-0 filter the strange substance came out of its container.

Obviously the channel with this filter was without an output signal, surely the filter is faulty given its pitiful conditions. I immediately start looking online for the component and discover that it is unobtainable, nothing to do.

All that remains is to see how it is made..., draw the scheme and make a new one.

After several attempts I manage to cliff the black and sticky substance with the lifeguard in the acetone. Finally the module is free, I proceed by analyzing the circuit and drawing the scheme. What a mysterious filter, even eight operational!

However, these are four active and distinct filters connected to the mass; therefore, even if it had failed, the signal should still pass. All that remains is to try immediately, with great surprise the "faulty" filter without the copper casing and the resin works perfectly.

Wow! So the various problems of this component are due to the deterioration of the resin, which certainly shorts the circuit causing various cracks during listening or in the worst case the total interruption of the signal.