Bias lights not working on LP70S

[smodtactical]

I took the side top panels, side panels and bottom panel off on my LP70S because I just wanted to take a look at the internals of the amplifier. I wasn't able to get the central top portion off. After I looked I reassembled everything but I noticed when I inserted tubes the board was a lot more floppy. I also noticed the bias lights no longer work and its almost like they are gone and I can't even see them in the hole.

The amp still works and sounds fine. I inspected all the panels and it seems the screws are in place.

Appreciate any help, thanks very much.

[admin]

Any chance this is a wire wedged somewhere that is deforming the circuit board? I would probably start by simply removing all the panels again, and putting them back on carefully. I know it sounds simple but I have fixed alignment problems on other gear just by going through the assembly/disassembly.

As for the bias lights, the first thing you have to figure out is are they functioning or you just can't see them due to the physical misalignment. LEDs like that rarely fail in my experience and it could be another potential component problem so we have to differentiate between the light failure or an issue that is causing the voltage to be out of the bias on/off sensitivity range.

[Big Dog RJ]

Mmm... this is another typical example of curiosity killed the cat! First of all:

1. Why on earth did you want to take a look inside?
2. What's there to look?
3. Are you some sort of technician?
4. If not then refer point 1.

Now that you've opened it up and can't "un-ring" the bell. There are a few things that may have happened. As far as I can remember when my "highly skilled and highly qualified" techie was servicing these amps, there's a very critical second board that's isolated on a sort of suspension system. This board is where all the tube sockets are located on. If and when removing this board, side panels... or any damn panel, you have to be very careful as not to mis-alingn these panels when installing back. It has to be done in perfection and only someone who knows what they're doing will know!

Now, trying to be more positive here... OTOH perhaps the bias lights weren't working properly earlier? Any idea on when they were working last and any signs of Output tube failures...? When was the last time you checked bias?

Usually check the bias at least once in 6 months, just to make sure bias/ idle current on each Ouput tube is upto spec. Then again, these bias LEDs are extremely robust, they last for decades! So far, I've never come across any of CJ's bias LEDs going out or failing, especially all of them.
I've come across cases where either one bias LED didn't work, and that happened on one of my monoblocks. It was a small resistor that needed changing, that's all. After which, the LEDs worked fine!

So basically looks like... whiles putting Humpty back together again, you've mis-alingned something. Oh just great mate... referring to point 1 above.

Truly hope someone can help you.
Best, RJ

[Big Dog RJ]

BTW, there's a great chap here who took apart his Premier 5's I think it was. Fully refurbed and sounding tops! He carefully looked after his amps and restored them like brand new! Only thing is Premier 5 era vs LP series... different planets but nonetheless he may know.

Try to get in touch with him, I'm sure he'll figure it out and can properly explain and guide you. Rather than having to take these to a qualified techie, putting them back together again the proper way... and charging you a bill.

Best of luck, RJ

[roberto]

Hola smodtactical,

You don't see the LEDs into their hole because they are not in the right position.
The first thing that you have to do is to take the whole PCB (print circuit board) apart again. Then straiten again the LED pins back again with much care. Before you put the screws back that secures the PCB, you must have the four LEDs into their position, and fully inserted into their hole. Yes, it is a difficult task, but it is the only way. With tons of patience you can do it. I use a waxed dental floss as a tool to have them in the right position. Perhaps you might find another easy way to do this task. You could make a hook with a cloth pin, and the pin secured into a long thin screwdriver or similar. Insert the hook into the top LED and address it to the hole. This is for all four LEDs. Then wiggling a little bit the whole PCB, they finally will get fully into their hole. Now it is time to put back the screws that secures the PCB in its position. Remember: don't tighten the screws that secures the PCB until the last screw is into its place.

Please excuse my bad English...I hope that you can do it!
Happy listening!

[Big Dog RJ]

Ah! Brilliant advice from our Robbo mate.

I may add, this also involves a very steady hand, must be absolutely focused and fully sober!
Definitely not for me, I'd probably break the pcb board in half. In which case, not only LEDs but nothing would work!

I'm sure with a steady state of affairs, you'll be able to get Humpty back together again. Let us know how it goes.

Cheers, RJ

[roberto]

Well, the trick is to have the four LEDs into their position, wiggling a little bit the PCB and then their screws. If you have unsteady PCB, this means that the secured screws are loose and need a retighten all of them. NEVER USE FORCE TO PUT THE LEDS BACK INTO THEIR POSITION.

[smodtactical]

Thanks so much guys. I stupidly installed the top plates the wrong way and covered the lights. Its ok now. Facepalm.

[smodtactical]

The pcb does seem a bit loose though.

[roberto]

The posts where the screws of the PCB are screwed, must be retighten at the chassis.

[admin]

Thanks so much guys. I stupidly installed the top plates the wrong way and covered the lights. Its ok now. Facepalm.

Glad it's fixed. Don't worry about it, we've all been there!

The pcb does seem a bit loose though.

Go back and makes sure everything is appropriately tightened down and aligned. If it was snug before all this started, it means it can be snug again. Sometimes the screw tightening order can cause these kinds of things to happen. I will usually keep screws loose at first with all them in the thread, and then only do final tightening when they are all in place.

[smodtactical]

Thank you sir