Woelke ME106E Wow And Flutter Meter ('Tonhöhenschwankungs-Meßgerät')
Woelke ME106E
This is a high-quality wow and flutter meter from around 1978, built by WOELKE MAGNETBANDTECHNIK, Munich, Germany. It can measure drift(wow) up to 5%, flutter up to 3%. The smallest scale in both measurements is 0.1%. It can use NAB or DIN type of measurements, based on 3150 Hz test frequency. An external filter can also be looped into the signal path. It offers several outputs for feeding the resulting signal into some recorders or other devices. Finally, it offers calibration signals for 5% wow and 0.1% flutter. It detects a valid signal on input connection by showing a green light if there is a signal.
My device was broken and I had to do a small repairment.
Images from inside
On this PCB the multivibrator transistors for creating 3150 Hz (2xBC107) can be seen on the upper left. There is also a Z-diode on the top, which creates a highly stable 6.2V voltage for that multivibrator from the +18 volts regulated rail.
Another small PCB, I guess for input processing:
Input processing area. We find two FETs 2N4391 here:
The device is more complex that I thought, using in total 16 OpAmps (13xLM307, 3xLM301) to implement its functions:
Solder side of PCB. A few design afterthought elements are manually soldered there:
Repair
The device did not work on arrival. The power cord was cut off, I replaced it. Then it shows maximum drift value and zero flutter, independent of input signal.
I found that the 3150 Hz signal was not generated. A multivibrator consisting of 2 BC107 transistors and one OpAmp are generating that frequency.
The multivibrator is powered by 6.2 volts, created by a zener diode from 18 volts rail. I found that no voltage was there. Candidates for failure could be a shortened diode or a shortened 100µF capacitor. I found that the capacitor was shortened. I replaced that capacitor, and the device starts working. There was no other fault inside.