MR 78 Panel Bulb Replacement

crmoudry

New Member
I would like to know the procedure for replacing the panel (above knobs) bulbs on a MR 78. I replaced the meter lights, wondering if I just remove the faceplate on the MR78 to access the bulbs? Also on the 7270 does anyone know the procedure to replace the meter bulbs with LED's?

Thanks
 
I would like to know the procedure for replacing the panel (above knobs) bulbs on a MR 78. I replaced the meter lights, wondering if I just remove the faceplate on the MR78 to access the bulbs? Also on the 7270 does anyone know the procedure to replace the meter bulbs with LED's?

Thanks
An easier way is to flip over the unit and remove the bottom cover. The bulb sockets are held in by V shaped spring steel clips. Squeeze them and retract the socket. When replacing it, put one side in first and then squeeze to get the other side in.
 
I would like to know the procedure for replacing the panel (above knobs) bulbs on a MR 78. I replaced the meter lights, wondering if I just remove the faceplate on the MR78 to access the bulbs? Also on the 7270 does anyone know the procedure to replace the meter bulbs with LED's?

Thanks

As far as the 7270, I just bought some LEDs that are replacements for the GE259 lamps in the 7270. The procedure to replace the lamps is to first remove the top cover held in by four screws, then carefully pry up the PCB that has the lamp holders soldered to it. You can then simply replace the lamps and pop the PCB back in. The LEDs I bought were too wide and I couldn't fit them back through the openings on the plastic lamp holder casing, so I just put in new GE259 lamps instead.

Replacing the meter lamps with LEDs is a bit tricky because you're going to change the color of the meters by doing so. They usually end up looking more purple. I've simply stuck with the original lamps in both my MC2205 and my MC7270.
 
lbcgav noted: *** Replacing the meter lamps with LEDs is a bit tricky because you're going to change the color of the meters by doing so. They usually end up looking more purple. I've simply stuck with the original lamps in both my MC2205 and my MC7270. ***

Personally, I agree with this, and not just because of the possibility of changing the color. LEDs are DC devices, and on older equipment like this, the lamp supplies are often AC. LEDs can create electrical noise as they switch on and off. To make matters more complicated, on later Mac amps, the engineers designed regulated AC supplies to keep the meter lamp intensity constant regardless of line voltage variations, supplies which assumed standard AC incandescent lamps were what they were driving.

Granted that this varies with the individual, but one other reason I dislike LEDs on AC supplies is that they flicker, like a computer monitor set at too low a refresh rate. This literally gives me a headache after staring at a component's front panel for more than a few minutes.

#259 lamps are still readily available at reasonable prices-- I'd go with them for your 7270.
 
There is an employee of a LED supplier who posts here every once in a while tooting his own horn about LED " upgrades".

Fussing with fit issues with the 18xx bulbs and color issues have soured me to LEDs.

Except for the MC2125 and MC 2155 with their small light boxes. Since the color in most cases has already yellowed, replacing with cooler running LEDs makes sense, you already need to change the blue filters inside the meter light box.
 
There also a large resistor on the MR-78 that can be removed to brighten the bulbs to match Mac pre's and amps better.
 
An easier way is to flip over the unit and remove the bottom cover. The bulb sockets are held in by V shaped spring steel clips. Squeeze them and retract the socket. When replacing it, put one side in first and then squeeze to get the other side in.
How do u get to the meter bulb for signal strength?
 
How do u get to the meter bulb for signal strength?
That is NOT easy. I haven't done it in years and I don't even own an MR78 anymore. If I remember, you have to remove the front glass AND remove or loosen the front steel plate behind the front inner glass that the meters are mounted to. You have to be careful regarding the dial stringing. They are vertically mounted with a blue plastic sleeve put over them. Please, someone correct me if I am wrong. I would definitely put LEDs in there.
 
There also a large resistor on the MR-78 that can be removed to brighten the bulbs to match Mac pre's and amps better.
Does anybody have a picture of this resistor?
Iam wondering why the MR-78s panel brightness is not the same as on the rest of the family (C32+MC2205)

Cheers Max
 
Does anybody have a picture of this resistor?
Iam wondering why the MR-78s panel brightness is not the same as on the rest of the family (C32+MC2205)

Cheers Max
I'll take some pics this weekend and post here, or in a new thread.
 
@Max2205 Remove the bottom panel and this is the resistor that needs to be removed, or simply jumpered for an MR-78 to be a bit brighter, matching other Mac components
MR-78 lamps.jpg
 
Hey again, thank you very much i will think about doing it myself. But maybe ill let a shop do it, since iam very untalented at soldering etc. :)
 
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