Owner`s manual

5
typically high input impedance of most tube circuits, simply leaving the inputs open will
probably cause stray signals to mislead your investigation. FYI – the output should be
connected as it would be normally (e.g. in a power amplifiers the speakers are
connected).
The steps are as follows:
1. Power Off
2. Starting at the power amplifier, remove the connections at the input and place the
RCA shorting plugs into the inputs.
3. Apply power and observe. It is important to make note of any changes that have
surfaced as a result of the test. For example, did the hum or hiss change? Changes
indicate that the problem may be interactive and not solely the result of one
defective component.
4. If the problem has been eliminated, it is reasonable to conclude that the isolated
component you are evaluating and all components downstream (towards the
loudspeakers) are not defective and that the defective component has yet to be
identified.
5. Power Off.
6. Reconnect the interconnects from preamp to power amplifier and remove all of
the inputs from the preamplifier. Place the RCA shorting plugs into one of the line
inputs of the preamplifier (for example, the tuner input) and select that input.
Power up the system and observe. If the problem is eliminated, place the RCA
shorting plugs in the phono inputs and select the phono (to determine if the phono
amplifier is the source).
Now that you have confirmed that the problem is with your Stereo 70, review the
remainder of this document and consult the section that most accurately defines the
symptoms observed.
IV. Digging In
If your amplifier that simply won’t power up, there is obviously no need to isolate it from
the other components. The first thing you should check is the fuse. If the fuse has
tripped it is possible but not probable that it was a fluke. More likely is that something in
the power supply is defective and has caused an over current condition causing the fuse
to trip. Replace the fuse with another of identical rating.
It is critical that you do not
increase the size of the fuse. Remember the fuse is a sacrificial device. If you increase the
rating of the fuse above the value specified, you reverse the sacrifice – in other words,
you sacrifice the amplifier to save your fuse! During all the tests that follow it is very
important to observe the time required for the fuse to trip. Note if the fuse trips
immediately or is delayed until after the amplifier “warms up” for a few seconds.