This is the upper drum used in the
The drum shown above has a solid brass mounting plate and was prone to wear causing a sticking noise on rewind. Sony produced a replacement version made of a hard alloy identified by the absence of the brass mounting plate.
A common symptom experienced on these machines is a thumping noise
during tape rewind. Another symptom on some machines is that the tape
'sticks' to the drum. These are both due to wear on the upper drum
All models will produce poor pictures when the video heads wear out. The upper drum wears at about the same rate of the video heads. So whilst the heads are being worn down, the drum is also wearing down. This in effect, extends the lifetime of the video heads as the end result is that they remain in closer contact with the tape. When a new head is put into the machine, without replacing the upper drum, it protrudes more than normal from the drum. This causes slightly more wear to the tapes but more importantly causes the head to wear at a slightly increased rate. By replacing the upper drum at the same time, this eliminates this problem.
A second reason for replacing the upper drum at the same time as head replacement is that if the drum is worn, it can make aligning the new head more difficult (i.e. the output off the head pre-amplifier cannot be made 'square'). Using a new upper drum can help this situation.
The lower drum wears less than the upper drum and will probably only needs replacing after a second replacement upper drum is needed.
First examine the drum to see if it is excessively worn. Looking
closely, you should be able to see the wear pattern of the tape across the
drum. If you feel this with your finger and there is a significant
ridge between where the tape passes and where it doesn't, then a new
upper drum is needed.
N.B. If the video heads are worn, it will probably be necessary to change them at the same time, even if picture quality is currently ok. Replacing the drum without replacing the heads will mean they no longer protrude or protrude less from the drum resulting in a sudden drop in quality. It is probably best to first try without replacing the head as video heads are not cheap.
Remember to record a tape and play it back, as this is where tape head quality can best be determined (i.e. with recordings).
Accessories required: Centering jig.
N.B. Keep it carefully after replacing the upper drum, as it will be used again when replacing the guide arm assembly. (It does not accompany the guide arm assembly).
Adjusting AGM rotary transformer gap
Thanks to Mark Perry for supplying this information