Hi everyone,
Here we go starting the final physical phase of the overhaul. This time I am re-capping the Playback Amplifier board. The two Head Amplifiers were done in the previous installment. Now to do the main Playback board itself.
The circuit diagrams in the Service Manual describe the Playback Amp as RWF-069, whilst in my machine this is actually an RWF-078. Some differences to be found no doubt. One that is immediately obvious is that the original RWF-069 supported a third daughter board, the RWX-155. This was the driver board for the VU meters, but this has now been incorporated into the main Playback Amp itself.
Due to these differences it is very important to proceed with this re-cap carefully. I basically did it one capacitor at a time so that I could verify the actual part against the Foil Side diagram from the manual. In doing this I found that the physical board held 4 more capacitors than indicated by the diagrams, 1 capacitor on the diagram did not exist on the board, and 1 capacitor had a different value than was indicated on the diagram.
So, without further ado, lets get on with it.
First I found it helpful to stand the machine on one end, with the Playback Amp at the top. I then dismounted the Control Assembly and it's alloy heat sink, moving them carefully out of they way. This gave a lot more clearance to the Playback Amp.
Here you can see the Control Assembly moved out of the way and loosely held by a cable tie.
Here is the Foil side of the Playback Amp. Complete with plenty of that goo that these boards seem to be sealed with.
And of course the component side, with the Head Amps still removed but all the capacitors replaced.
(This was supposed to be a shot with the original components still in place
)
This board does have a pair of 2SC1344 transistors, and according to the diagrams, a pair of 2SA672 transistors. I had intended
to replace these as a matter of course, but discovered that the 2SA672 were actually 2SA721's. Based on this I re-installed the
2SC1344's and the 2SA721's and left well enough alone. (Thanks to GPS16 for help with this)
After working through all of the capacitors, one at a time, I remounted the RWF-070 daughter boards. Here is the Foil side with them soldered back in.
And of course the component side with everything replaced. If you look carefully you will see that I have used WIMA film caps
for the smaller value ceramics and there are also two Murata C0G ceramics as well (the little blue drops). All in all this was a
slightly fiddly process as some of the components, caps and transistors are quite closely packed. I did make a few mistakes
unsoldering component legs that should not have been
But in the end it all came together nicely.
The left overs. (Although my notes on the top of the diagram say 3 extra caps, there were actually 4. You can see 3 of them,
1 x 22uF 35V (originally 10V) and 2 x 22uF 50V (originally 35V), on the far left of the diagram where I have noted their
approximate locations. Also, one ceramic was noted on the diagram as a .01uF but was in fact a .047uF)
The acid test. It still works! Sounds great too!
Next step will be to replace the very finicky VR's for Bourns multi-turn units. That should make re-calibrating the machine a LOT easier.
For now though, here are the parts used on the Playback Amp:
1 x Nichicon FG 220uF 50V:
https://www.mouser.com/ProductDetail/Nichicon/UFG1H221MHM
5 x Nichicon FG 22uF 50V:
https://www.mouser.com/ProductDetail/Nichicon/UFG1H220MEM
4 x Nichicon FG 10uF 50V:
https://www.mouser.com/ProductDetail/Nichicon/UFG1H100MDM
2 x Nichicon FG 2.2uF 50V:
https://www.mouser.com/ProductDetail/Nichicon/UFG1H2R2MDM
13 x Nichicon FG 4.7uF 50V:
https://www.mouser.com/ProductDetail/Nichicon/UFG1H4R7MDM
1 x Nichicon FG 1uF 50V:
https://www.mouser.com/ProductDetail/Nichicon/UFG1H010MDM
3 x WIMA .047uF 100V:
http://mouser.com/ProductDetail/WIMA/MKP2D024701C00JA00
2 x Murata 22pF 100V:
https://www.mouser.com/ProductDetail/Murata/RDE5C2A220J0P1H03B
And here are the measured values of the old electrolytics etc:
220uF 35V -- 252
22uF 35V -- 29, 27, 29
22uF 10V -- 29, 30
10uF 16V -- 14
10uF 35V -- 13, 15, 14
4.7uF 35V -- 5.99, 5.87, 5.85, 5.77, 6.05, 5.89, 5.78, 5.68, 5.26, 5.87, 5.73, 5.82, 5.78
2.2uF 50V -- 2.82, 2.72
1uF 50V -- 1.60, 1.45
.047uF Ceramic -- .040, .045, .052
22pF Ceramic -- 22, 23
That's it for this installment