HP (Hewlett-Packard) HP 85660B ユーザーズマニュアル

Table 1 correlates CRT phase-lock error messages with the probable faulty phase-lock loop
and associated assemblies. This is especially helpful in determining the faulty loop when more
than one phase-lock error message is displayed.

Table 1. Troubleshooting Using CRT Unlock Messages

Message

Probable Faulty Loop Associated Assemblies

(UNLOCK)

Phase Lock Loop 1

 to 

PL2

Phase Lock Loop 2

 to 

REF

Reference Loop

 

 A22

YTO

YTO Loop

 A20, A21, All

M/N Loop

 

HET

Heterodyne Loop

 

 PL2

Phase Lock Loop 2

 to 

 YTO

Phase Lock Loop 1

 to 

 PL2, YTO

Phase Lock Loop 2

 to 

REF, 

 PL2

Reference Loop

 

 A22

REF, M/N, YTO Reference Loop

 

 A22

M/N, YTO

M/N Loop

 

HET, REF

Reference Loop

 

 A22

Phase-lock loop troubleshooting is much easier if it is understood how the start frequency

is derived. The Diagnostic Functions of the spectrum analyzer can also be used to simplify

troubleshooting of the phase-lock loop.

The simplified block diagram at the back of this chapter shows the assemblies involved in
setting the start frequency. The HP 8566B has two tuning modes. For frequency spans

greater than 5 MHz, a method called lock and roll is used. This basically involves phase
locking the analyzer start frequency during the retrace period prior to the beginning of a new
scan. For frequency spans of 5 MHz and less, the YTO Loop is phase-locked during all of a
sweep, and the stable 

 Loop PLL2 is swept.

4 Analog Troubleshooting