[Vintage Pete]

Originally Posted by altbrewer

At least it's a mystery to me. Maybe somebody can help.

I just got an MR78 (can't believe how good FM can sound). It is in fantastic condition, but the lettering above the knobs doesn't light up. I can see a dim glow in the lettering when I look at it from above, but from straight on I can't even tell there is any lighting at all. The dial and meter lights are fine, although dimmer than my newer gear.

I thought it was the bulbs, but when I opened it up, all the panel lights were good and lit up when turned on. I do see a clear plastic panel with holes for the panel lights to fit into, attached to the inside of the faceplate. I assume this is some sort of light guide to light up the lettering, but I don't think it is working. However, I do not see anything obviously wrong with it.

Any ideas? Or, is it normal for the lighting to be so dim? I will try to post pictures, but this is a busy weekend for me; my son is getting married.

Thanks,
Mike

I had the same issue with my MR78. The dial lighting was fine but the lighting across the lower portion of the panel was extremely dim. I puzzled over it for some time. Then, once I acquired a service manual I figured out the reason. In series with the panel filiment circuit is a 2 ohm, 5 watt resistor that prevents the filiment circuit (which is comprised of type 1866 bayonet style bulbs) from receiving the full 6.3 volts from the secondary winding of the power transformer that powers the circuit. You need to remove this resistor, as I did, and replace it with a jumper wire to complete the circuit and optimize the brightness. The resistor is designated as R508, and is located in the underside of the tuner chassis near the rear of the unit. As I recall it is soldered onto a stand-up, hard-wired terminal strip.

I'm not sure what the reasoning was here, with having this resistor in the filiment circuit in the first place-all it does is give you a very dim bank of lights. Perhaps it was intended to extend lamp life-but I removed (bypassed) this resistor over 8 years ago, and have not expreienced any issues with a shortened lamp life. You may also want to check to be sure that the correct lamps are installed in the sockets across the lower panel-they should be type 1866 bayonet lamps.

I seem to remember taking some photos of the area of the tuner where the resistor is located. I'm not finding them right off the but but I'll keep looking.


I hope this helps-enjoy your MR78. It'san awesome and beautiful tuner.


Pete