Explanation Of Signal Names; Voltage Values In The Circuit Diagrams - Fluke PM3082 Service Manual

3 - 4
3.1.3

Explanation of signal names

Throughout the circuit diagrams signal names are used. These names make it easier to trace a signal
going from one circuit diagram to another. In many cases the signal name and also the component
to which a certain node is connected are given in the circuit diagrams.
For every printed circuit board a signal name list is shown in alphabetical order. It shows:
- The meaning/function of the signal.
- The signal source(s).
- The signal destination(s).
Signal names are chosen up in a logical way. Basically signal names (e.g. MTBPPLEV-HD) consist
of two parts:
- A functional part with a maximum of 10 characters (e.g. MTBPPLEV). The part is arranged such
that recognition is easy.
- An extension with a maximum of 2 characters (e.g. HD). The extension is not always used.
The first characters (e.g. MTB) in the functional part indicate the part of the oscilloscope. Examples
are:
- AT 1, AT2, AT3, AT4: the input attenuators of channel 1,2,3, 4.
- PA1, PA2, PA3, PA4: the preamplifiers of channel 1,2 ,3 , 4.
- FNC1, FNC2, FNC3, FNC4: the function selection parts of channel 1,2,3,4. MTR: main time base
triggering.
- MTB: main time base.
- DTR: delayed time base triggering.
- DTB: delayed time base.
The last set of characters in the functional part (e.g. PPLEV) indicates the function: in this example
Peak-Peak LEVel triggering is switched on/off.
The first character of the extension indicates if the signal is active when high (H), active when low
(L) or that this is not fixed (X, for instance the output of a counter).
The second character of the extension indicates the kind of logic. Possible abbreviations are: T
(TTL), E (ECL), A (analog signal), C (CMOS 12 ... 15V) and D (CMOS 5V).
3.1.4

Voltage values in the circuit diagrams.

Throughout the circuit diagrams voltage values are indicated. This facilitates fault finding in the
vertical channels, triggering, time base and final amplifiers. Most of the voltages consist of an AC
signal superimposed on a DC biasing voltage. Some of the AC voltages are small. They must be
measured with an oscilloscope via a 1:1 probe and AC coupled input. The DC signal component is
bigger and must be measured with the measuring oscilloscope with DC coupled input. The nodes
where a signal can be measured are indicated with a dot on the p.c.b. lay-outs.
The oscilloscope under test must be prepared as follows:
- Connect the CAL voltage via a 10:1 probe with indication ring to the input of the suspected
channel.
- Press the STATUS and TEXT OFF key simultaneously to get a defined starting position.
- Press the AUTOSET key
- Put AMPLA/AR of the active channel to 0.1 V: this should give 6 vertical divisions of signal on the
screen.
DESCRIPTIONS