Jerry's TV
Active Member
Did you check the lamp continuty when removed from the receiver? They need to be out of circuit or you will measure continuty of the other lamps and the transformer winding.
Pictorial how to: LED tuner bulbs in SX-x2x (727 used)
- Thread starter Johnny_Law
- Start date
jc339
Active Member
Hello Super Member Ivandezande, Thanks for sending the diagram above. I'm still working on it as I have very basic knowledge and want to be careful not to damage anything more important than radio dial back-light bulbs. Please add any ideas you may like to.
Jerry's TV also sent me some info and I replied to him here...http://audiokarma.org/forums/index....dial-lights-5-fuse-type-bulbs-mystery.926422/
Jerry's TV also sent me some info and I replied to him here...http://audiokarma.org/forums/index....dial-lights-5-fuse-type-bulbs-mystery.926422/
There is something that fools many people, the "sneak" current paths. Like back through the transformer!!
In the above diagram F2 can be blown, and everything will LOOK good on an ohmmeter. INCLUDING F2!!
You need to remove each component and test it out of circuit.
IF a new F2 blows immediately, one of the lamp filaments that burned out could have welded itself across the lamp contacts somehow - it has happened.
Measure the VOLTAGE at each lamp (8v AC), and across the fuse (ok = very low voltage, bad = 8v AC)
The OHMS of your ohm readings are very important.
You CAN, using the 10 AMP CURRENT scale and connections of a meter, connect to either side of a fuse that may be blown, and read the current that now flows through the meter's resistive shunt substituted for the missing or blown fuse. NEVER try to take a voltage reading with the CURRENT setting still engaged in the meter - things will BLOW UP/
In the above diagram F2 can be blown, and everything will LOOK good on an ohmmeter. INCLUDING F2!!
You need to remove each component and test it out of circuit.
IF a new F2 blows immediately, one of the lamp filaments that burned out could have welded itself across the lamp contacts somehow - it has happened.
Measure the VOLTAGE at each lamp (8v AC), and across the fuse (ok = very low voltage, bad = 8v AC)
The OHMS of your ohm readings are very important.
You CAN, using the 10 AMP CURRENT scale and connections of a meter, connect to either side of a fuse that may be blown, and read the current that now flows through the meter's resistive shunt substituted for the missing or blown fuse. NEVER try to take a voltage reading with the CURRENT setting still engaged in the meter - things will BLOW UP/
jc339
Active Member
Thanks markthefixer for your comments and help. Your warnings are very profound but I think over my head a bit. Jerry's TV helped me by showing me how to measure the ac volts on the PCB and then once we determined we indeed had 7 v AC I removed each dial light bulb, all 5 were blown, with no continuity across any of the old bulbs when removed and tested out of the SX-727. Actually Jerry's TV suggested that I remove the bulbs from the tuner first and check them out of the unit. I didn't do it in that exact order but removed them after we tested got the 7 v AC on the PCB. (I think I wondered that all 5 bulbs would be blown out, but I later thought that some of the bulbs might have burned out at different times and the remaining bulb or two were giving enough dial back light and I probably didn't notice it until they all eventually burned out. I know I sound dense and that's not a false assumption.) At the top of this post, Jerry's TV says, "Did you check the lamp continuty when removed from the receiver? They need to be out of circuit or you will measure continuity of the other lamps and the transformer winding." You guys are awesome! I ordered all new bulbs from Dwojo.com - dial light warm white LED's and installed them and they work great. I also ordered and installed one burned out AUX function bulb. I soldered that in to the board. Here is where I am so far on the SX-727 (I purchased it in 11/1973 for $419.95 - 45 years ago 
) The bulbs are the only things known to me that have gone bad in all that time...
) The bulbs are the only things known to me that have gone bad in all that time... GeraldGarner
New Member
What happened to all the pictures on page 1?
GeraldGarner
New Member
Well thank you for the reply. I myself just purchased some warm white LEDs from eBay due to this post's recommended bulbs reviews saying they are too bright. I also went into my SX 828 looking for the meter bulbs and ended up taking off the black metal piece that holds the tuner dial, dimmer, and FM muting buttons as well as those parts. However, I found out that the bulbs were held in the metal piece that is near the Tuner thread tensioners on the left and I didn't have to remove the black metal piece. I was able to put it all back together well but I want to do some more intricate work on this thing and 828s don't have a lot of visual media to show how to do this. I wish the professionals would do some more youtube videos or take pictures so those who want to DIY to save some money can follow along. It makes me want to buy a GoPro esque camera and a head mount to document it for people like myself.
