SR-52A rebuild project (SR-52A 942058 LTA4176)

[albertofenini]

Card reader works, reads and writes

Hello Everyone, the card reader is now working

First we disconnected the card reader and checked the resistance for every channel
Yellow with Black : 681 Ohm
Green with Black : 675 Ohm
Orange with Black : 700 Ohm
White with Black : 718 Ohm

we do not have (yet) an Impedance Meter so we couldn't check those values as well
but never mind, the head looked ok, we polished the face of the magnetic head with
a Dremel and a cotton tool, is less aggressive than using the cleaning card which is
abrasive and has the same effect as for removing the dirty patina

one thing we learned todays is that rather then putting oil in order to lubricate
the card reader motor (we were using WD-40) is way better to use a contact
cleaner (we uses Deoxit D5)

we think this is because probably the reason for a noisy and slow motor is that the electric brushes
that can be seen from the bottom removing the small black cover are oxidized and the contact cleaner
makes miracles, now the motor is fast and way more silent than before

Then we removed the TMC0595 (our is a version D, it was printed on the bottom)
We cleaned underneath and we also removed and checked all the capacitors C12,C2, C3, C4, C5
checked the nominal value and in the end we used those from the other spare unit as they were .004 microF
which was closer than the original ones to the nominal value of .005 microF

Meanwhile we discovered and fixed (again) the keyboard that had a loose joint for the fifth column which made
Impossible to do any calculation being that the column with the operation keys and the equal key

Re mounted everything and ... voila

It reads all of the BA Libray and we have also been successfully copying the card BA-1
Diagnostic cards also produce the expected result

Next step : check the faceplate and close everything ....

We may as well try the same operation on the other spare unit, but first we need to find a good
SN27882 because we took one from that unit to repair this ...
It's available new on line or it can be found on all of the SR-50 models

Picture and video updated here : SR-52A rebuild project (SR-52A 942058 LTA4176)