Pioneer QX-949 Scope Lamp Replacement with LEDs

[Brivan]

I've got a nice Pioneer QX-949 that I replaced scope lamps with 4mm LEDs but, due to the 90-degree angle the LEDs are at with the holes in the back of the scope, very little light is getting through to the display. What's everyone been doing to get around this?

Thanks!

 

[audiojones]

I replaced mine with incandescent bulbs of the same voltage and diameter as the originals. IIRC I think I tried LEDs and ran into the same problem.

 

[Brivan]

I replaced mine with incandescent bulbs of the same voltage and diameter as the originals. IIRC I think I tried LEDs and ran into the same problem.

Thanks for the quick reply. I considered replacing the lamps with standard incandescent, but I wanted to stick with LEDs, if at all possible. I ended up using bare lead 4mm clear LEDs without the silicone lamp holder. I bent the LED pins at 90 degrees right next to the LED globe, then fitted the leads to the PC board. It worked out pretty well:

 

[Brivan]

Now, I'm onto replacing the function indicator lamps. My standard long lead 4mm LEDs won't fit in the holder, so I'm looking at using 3mm, instead. Wondering what most folks have done here, as well?

 

[markthefixer]

Well, in other models I used standard 5mm LEDS that I chucked up in a drill and used a file to turn down the rim to the body diameter or slightly smaller.

edit: Body Diam 5mm, rim dia 5.8mm

Had to use care to not hit the pins. Then it would fit in where the incandescent function leds came out of, all the way up to the SX-3900.

I have not heard of 4mm leds as an established size. I am researching it now.

edit: mouser gets 22,000 hits for 5mm leds, and 26 for 4mm leds. and they are oval.

The 3mm LEDS I used in the past were too small for the function indicator lamp holder, thus the turned down 5mm.

 

[Brivan]

Well, in other models I used standard 5mm LEDS that I chucked up in a drill and used a file to turn down the rim to the body diameter or slightly smaller.

edit: Body Diam 5mm, rim dia 5.8mm

Had to use care to not hit the pins. Then it would fit in where the incandescent function leds came out of, all the way up to the SX-3900.

I have not heard of 4mm leds as an established size. I am researching it now.

edit: mouser gets 22,000 hits for 5mm leds, and 26 for 4mm leds. and they are oval.

The 3mm LEDS I used in the past were too small for the function indicator lamp holder, thus the turned down 5mm.

Hi, Mark

Nice to hear from you, again. I've used mainly 4mm long-lead LEDs from Dave Wojnarowski for quite awhile. I just measured the body of the most-common type I use from him and it's right at 4mm.

I considered using a drill on the rim of the sleeve in the lamp holder to allow for a larger LED, but was afraid the sleeve would either just spin or it would grip enough that it cracked the brittle old lamp holder. I've only pushed out one of the sleeves, so far, and I may encounter trouble with the others, so drilling might be my only option.

With the lamp sleeve removed I can get a 4mm long-lead LED assembly inserted into the holder so the body protrudes through about the same distance as the original lamp. A 5mm LED will only go in far enough for the body to clear the hole, but the rim catches on the edge. Either type would work here, I guess - maybe using the backed-off 5mm LED would help to eliminate spotlighting on the back of the dial scale.

As always, thanks for your years of wisdom here on AK!

 

[Brivan]

All lamps on the QX-949 have now been replaced with LEDs. Some notes about the 4CH-CD4 indicator:
4CH CD4 (pins 9 & 10) (red dot) lamp will only illuminate when function selector is set to phono, mode selector is set to 4CH-CD4 and a ~30kHz carrier signal is fed to the appropriate phono input. When <>30kHz signal is fed to the phono input, ~8v will be measured at pins 9 & 10 with the lamp disconnected, but only ~2v with the lamp connected – supply current isn’t increased until the input frequency is ~30kHz.

 

[Brivan]

A final note on the QX-949: After allowing it to play for a couple days, I started to get the classic "snap, crackle, pop" noise in the front left channel. I ended up pulling both power amp boards and replacing the notorious crappy transistors - 2SA726 & 2SC1451. Problem solved. I made detailed notes of the wires going to power amps, since there's 51 that need to be removed. Since it took a fair amount of time to draw out, I thought it might save someone time if they have to remove the power amp boards like I did. I'm assuming all QX-949 receiver power amps use the same color wires, but it would be a good idea to verify your receiver with the list below before proceeding. Wires are smaller-gauge unless noted.