I would suggest to demagnetize and clean the heads before going
farther. Also, use a tape cassette that is not very old. After these
cassettes are a number of years old, the permability of the magnetic
coating may deteriate with age.
When these decks are calibrated, a proper test reference tape is used
to align the playback first. Then for the record section we use a know
standard type fresh high quality recording tape, and an audio
generator to reference the response of the machine. There is a test
reference tape for dolby, and one for no dolby. There are also test
reference tapes for metal, and ones for the different types of oxide
tapes.
For properly setting up an audio tape machine you will need a scope,
audio generator, reference standards tape, a high quality recording
tape if each type that the machine is supposed to use, and a VU meter.
The service manual should have the details of how to set the machine
up.
There is the combination of the capston speed, tape tension, azmuth,
head height, head postion, guide adjustments, pinch roller pressure,
and then the adjusting pots for the EQ's, levels, and Bias settings to
be set up. This is just to mention a few things that can effect the
performance of your audio tape machine.
In the lower cost machines they average out many of the adjustments,
for the different types of tapes to be used.
If the sound is not distorted, or is not out of ballance, and it is
uniform, I would just do a head cleaning and demagnetization. I would
not venture in to the alignment of the unit, unless I was prepared to
go all the way with proper servicing, and the proper checks. You can
probably find a head demagnetizer at most audio HiFi stores. Radio
Shack used to sell them. You can use some rubbing alcohol and a soft
tissue to clean the heads.
Most of the non factory authorized shops may have some type of test
reference tape and an audio generator, and do a simplified alignment
with the scope. This is not going to be a truely accurate alignment.
Considering the age and the value of your machine, is this all worth
it. Also, the performance of the machine may not be very stable unless
it is a very expensive unit, and there are no parts inside that have
become off specs from age.
Before doing any adjustments, it is very important that the
electronics, and the mechanics of the machine are working as best as
possible to specifications. If not, and you start to make adjustments,
the situation can be made worse.
Jerry G.
========
"tempus fugit" wrote in message ...
Hey all;
I've got a Technics tape deck (RS-B18) that is about 20 years old. I had
some problems with intermittent channels (rec and play) and took it apart to
see what I could do. I found a cold solder joint in the signal path and
resoldered it, which (so far, anyway) has fixed the problem.
However, there are a few things I'm wondering about. First, the levels (as
indicated on the meters) are lower in playback than record. IOW, if I record
a cassette with the levels reading around 0, the tape will play back with
the levels at, say -3 or so. It also varies depending on how the noise
reduction and bias is set:
1. No Dolby, CrO2 - levels are pretty much the same
2. Dolby B, Cr02 - levels slightly lower on playback
3. dbx, Cr02 - levels considerably (3 - 6 db) lower on playback
4. any or no noise reduction, Metal - no playback at all (this has been a
problem since I got the deck)
I can post more combinations if need be, but I hope that this will give the
general idea. I also cannot remember if this was the way things were going
before the repair (I think it was though).
Are these type of discrepencies normal, or can/should I adjust things to
equal them out?
I also noticed that the playback was a little dull after the repair (to be
honest, I hadn't used the deck in quite a while, so it may be the way it
always sounded). Would this be a bias setting that I may have inadvertently
moved while repairing? or perhaps it needs some adjustment in another area?
Thanks
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