Restoring Bruel & Kjaer 1023 Sine Generator = Help!
This is my all time favorite sine generator. In fact, it is not doing this equipment justice, just to call it sine generator. For example, the compressor (feedback) function is super handy if you want to compensate the irregularities in the driving transducer and measure the frequency response of an -say- accelerometer.
Anyways, it was in total dark, cold, non-working state when I received it. Fixed the power supply to generate the needed voltages without any ripples and discovered that, it is working in a narrower frequency band than the usual 20Hz to 20kHz. The sweep cuts early in the low frequency direction (nothing below 80Hz) and at high frequency region, there is nothing above 15kHz. The digital display goes dark at both directions and it cuts out the output. In between frequencies, everything works perfect. Frequency is spot on, output voltage is exact.
The only service manual which is on the web has the signal generation schematic blurred, I can not make out anything from the values or component IDs. Also, there is a mechanical switch that stops the generator when the dial is turned outside the scale limits. I have checked that and there is nothing wrong with its' operation.
Any idea, on where to start troubleshooting this problem, would be very much appreciated. Needless to say, I have already replaced the electrolytic and tantalum capacitors.
Thanks in advance,