Adcom GFA-5802 User manual

ADCOM Service Bulletin
Date: August 12, 1998
Ordering Matched FETs and Service Manual Corrections
Model #: GFA-5802
Bulletin #: GFA-5802-1
The GFA-5802 Service Manual notes on page 4that a number of the MOSFETs in the
amplifier are matched to ensure proper
performance~ For repairs requiring replacement of
these parts, equivalently matched parts must be used. In ordering these parts, these
procedures must be followed.
Failure of 0169, 0171, 0176, 0178, 063 or 073
For repairs requiring replacement of anyone of the transistors in input pair 0169 and
0171, cascade pair 0176 and 0178 or second differential pair 063 and 073, both
transistors
in the pair must be replaced. That is, if 0169 fails, both 0169 and 0171 need
to be replaced. Order both and specify
Matched with the part number.
Failure of any of the IRF244 output transistors
The category of the output transistors is identified by aletter written on the bottom of the
transistor. The markings will appear
in one of two ways.
1) As asingle or double repeated letter. (Example M or BB. Note: Band BB are different
categories).
2) As asequence of letters separated by adash. (Example AD-AA or TB-O).
When ordering replacements, indicate Matched with the part number and the exact letter
code written on the transistor. The replacement parts will be of the same category.
Note: there is no quality difference between transistors of different letter categories.
Transistors of category CC are not better than those of category
D. It is only important that
the output transistors are of the same category
for proper operation.
GFA-5802 Service Manual Corrections
1) On page 1, change step 4of the BIAS ALIGNMENT procedure from
"The reading across these resistors should average
33mV and all should be between
23mV and 43mV." to
"The reading across these resistors should be a
maximum of 33mV and all should
range between 18mV and 33mV."
2) On page 3, change the 062, 63, 73 part description from "*Matched IRF961 0" to
"*Matched IRF9622" and the part number from 33009610 to 33009622. IRF9610s will be
replaced with IRF9622s. These will be provided
in matched pairs as described above.
ES 8/98