Mullard radio MAS231 (Algemeen)

door Pandu Rajan , 09.04.2018, 09:39 (2421 dagen geleden) @ Pandu Rajan

Dear friends
In continuation of my earlier message I am giving the other jobs done on the above set. As there were some limitation on the length of the msg I am giving the remaining jobs done in this msg.
25. Replaced 5Y3 with the original rectifier valve AZ31.
26. Switched ON the set and measured all the voltages and found them nearly O.K.
27.Replaced R53 and R54 which were out of tolerance.
28. MW , LW and SW3 bands Started working. SW2 and all the band spread bands were not working.
29. One of the connection of the coil S33 was open. Repaired the same and SW2 became O.K.
30. Volume control was defective. Replaced the same by value 200K + 650K as the original value of 500K was not available.
31. Tone Control found O.K.
32. Somebody had put Valve 6K8 in place of ECH35 in position B2. Replaced with a new ECH35.
33. All the band spread bands were not working. Checked thoroughly and found the ferrite cores of all the 8 oscillator coils damaged. I am attaching a photo which shows the different types of damages to the cores.

a. The ferrite core was cut. It was Glued with super glue. This was for the bands 16m,19m and 31m.
b. The core was cut and the remaining part of the core attached to the brass screw was damaged and not repairable. Fixed a small Brass/Nylon tube to the core with super glue and inserted the brass screw into the tube and fixed with the super glue. This was for bands 25m, 41m and 49m.
c. the third type of damage was that the core itself was missing and only the brass screw was there. Luckily I had spare cores and adopted the same procedure as in ‘c’ and was able to repair the core of 13m band and the coil S107/S108.
e. I was unable to repair the coil for the 11m band as no further cores were available.
34. Aligned all the bands of the set as per the service manual except the 11m band.
35. All the 11 bands working correctly.
36. Band indication pulley was broken and was repaired.
37. As the separator plate between the transformer and the output valves EL33 was missing, provided a new one.
38. Made a new Dial. I am very thankful to Mr. John Pearson who was kind enough to provide the original scan of the dial and also the clear photo of the four clamps which keep the dial in position. As all the four clamps were missing it had to be made new.
39. The cabinet was completely restored.
40. Fitted the chasis into the cabinet and completed the restoration.

Regards
P.Rajan