Tuesday, April 17, 2012

More Marantz 2130 pictures

Well, as I expected, the underside of the Marantz 2130 is covered with circuit boards.  Combined with the RF and IF circuitry on top, there is quite a lot of stuff in this tuner.  I started examining underneath the tuner on Saturday night.

The power supply in middle center looks about as big as in a Kenwood 600T, however it should be noted this one here also supplies power for the scope.  There are some nice looking large Nippon Chem Con capacitors in that power supply, and nothing looks underrated, no sign of cooking (as with the undersized resistor in the Sansui 9900).  The MPX board is on the middle right. The board in left front is the buffer board which includes features such as high blend and the oscillator.  Somewhere the quartz lock board is tucked in.

Above is a closeup of the MPX board.  In there is a Hitachi HA11223 mpx chip with external switching transistors.  The big modules on left are 38Khz subcarrier filters...those need to filter down to 22Khz.  The MPX board uses a pilot canceler implemented with discrete circuitry to remove the 19Khz pilot from the output.

Above is a closeup of the power supply board.  There are 3 heatsinked semiconductors on the right, and one in a larger heatsink on the left.  In addition to the fuses on this board, there is a fuse on the case.

Above is a closeup of the buffer board.  Both the mpx and the buffer feature single 4558 output IC's and relatively large electrolytic capacitors.  I worried a lot about the black dot on the large capacitor near the center of the photo.  I wondered if it had been painted on and in fact it's hard to tell as there is no other sign of leakage than the back mark and a slight depression where it is.  If it was caused by having a leak once, it appears to be completely sealed now.  It turns out to be a capacitor in the oscillator circuit, so I'm not too concerned about it.  However, the entire tuner did have what I often consider the "bad capacitor" smell.  I doubt that it all came from the one above, but it might have.  I washed and dried the entire exterior case over the weekend, allowing each piece ample time to completely dry.  I wiped bare chassis metal, and transformers, and accessible parts of the scope.  Everywhere I wiped in picked up some brown, perhaps some previous owner was a smoker though it doesn't small like smoke as such, it smells like bad capacitors.  All the cleaning reduced but did not eliminate the smell.

At first, I had some trouble getting the bottom cover back on.  It's held in place with screws around the perimeter, and only goes on one way, but one of the screws, toward the backright corner near the RF connections, is extra long, and apparently intended to make contact with the metal of the RF shield.  It has to be jammed in just so or the cover cannot be screwed on as it bulges near that corner.  The bottom cover itself is rather thin metal to be supporting such a heavy unit--or even a light unit.  It flexes easily.  This appears to be another design feature.  When the unit is put down, the bottom metal panel flexes enough so that unless your surface is very uneven, all 4 hard plastic feet will touch the surface underneath them.  But don't pile too much equipment on top!  When I push down on the top of the tuner, I can feel the metal plate underneath giving slightly.  This could also be a cultish audio feature in the sense that the bottom metal panel is undamped and therefore "live".

I washed the bottom panel first, then let it dry overnight because I was going to bed anyway.  The next day I put the bottom back on, and then took the top off for washing.  At that point, I noticed a serious fault in the tuner.  The wire going to the tuner position indicator light is sagging down onto the IF board.  As you tune from low to high and then back down again, it catches on various parts on the circuit board, including the very critical and valuable SAW filters.  Over time, this could cause misalignment or serious and possibly unrepairable damage to the IF board, which is the very heart of this fine tuner and the key to its above average performance.

I was unable to find in the manual how this is supposed to be done.  Perhaps the wire originally was stiff enough that it didn's sag in the middle, or perhaps (and most likely) the wire was surrounded by a piece of heat shrink either from the dial side or the other side (the wire was originally attached to a wire clip on the cover of the RF unit).

Heat shrink might be the best solution, but it would require at minimum unsoldering the lamp without damagin the plastic, a very tricky operation.  That might have been why Marantz Service didn't fix this.  Perhaps the original heat shrink got damaged and was jamming the dial, so they just removed it, and didn't bother to replace, not realizing that the above problem could occur.

I came up with a fix that did not require any soldering.  I cut a nylon wire tie and placed it across the valley of the inside of the tuner from RF cover, where the now unused clip for the lamp wire is, over to the dial, where it is jammed between the circuit board and the dial plastic.  As the indicator moves across the dial, the wire tie supports it in the center about an inch from the circuit board at worst case (shown in picture).  Most of the time, it is much higher than this.  It took about an hour of tweaking to get it this good.  I still worry about a number of things, including the possibility that over time the vinyl covering on the lamp wire will wear off rubbing against the nylon tie.  But I suspect that won't happen fast, if at all, and hopefully just disable the lamp or blow a fuse.

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