BeePre2 - filament voltage power supply [resolved]

[Yossihaimberg]

When I’m checking the filament voltage power supply, I’m reading only 1.2 volts (supposedly should be 6.3 volts).

What do I do?

[Paul Birkeland]

Can you post some photos of your build so far? Can you measure the AC voltages coming into the board from the power transformer?  Are all the capacitors installed in the correct orientation? (and the rectifier diodes?)

[Yossihaimberg]

Here are the pictures, and the voltage tests.

Thanks

[Paul Birkeland]

The wires that leave that board and connect to the 4 pin socket aren't connected to the correct places on that filament board (they do not connect to the DC pads on the front side of the board, those should be left empty).

To the naked eye, I do not believe you have the correct resistor values in the R1 and R2 holes on this PC board.  It is extremely important to double check resistor values with your meter if you aren't 100% sure that the colors are correct, or if they are too hard to see.  I think (at minimum) that they are switched in the place where I am looking, but the 1K resistor I see has some unexpected colors, so this needs to be double checked.

If you have 1-2V coming off the front pads on that PC board, then I'd want to see what the soldering looks like on the bottom of the board, as it should be more like 8V (especially if there are no 300Bs plugged in).

[Yossihaimberg]

Hi, I corrected the filament problems, and I think it is now as it should be. HOWEVER...  I'm measuring 120VAC at the power source (plug), but I get no output from the transformer. I checked the voltage at 7 and 8 and it is 0....  The same at 11-14 (should be 6.3V) and 12-13.

Please advise.

[Doc B.]

Make sure the cord is plugged in all the way at the amp and check the fuse.

[Yossihaimberg]

I double-checked the plug/fuse. All good.

I think that while replacing the resistors (especially the 237 ohms) I damaged the board while trying to remove the soldering. The attached pictures show the possible damage. I'm reading 6.3VDC on the left side of the board, but only 1.2 VDC on the left side.

I'll appreciate your thoughts, and if I did damage the eyelet where the 273 ohm goes, is there a way to fix it?

Thanks!!!!

[Yossihaimberg]

I mean 6.3VDC on the RIGHT side, and 1.2 VDC on the LEFT side. Sorry

[Paul Birkeland]

What DC voltage to you get across the pads we don't use on the front side of the board for that side of the filament regulator board?

What value do you get if you try to use your meter to measure that 237 ohm resistor?

[Yossihaimberg]

1.2 VDC and 237 ohms

[Paul Birkeland]

I would reflow all of the solder joints on that side of the filament regulator board.

[Yossihaimberg]

I did check all soldering points and they seem to be OK.  Here is a summary of the measurements (as I think I misinformed you earlier, sorry...0:

Right side - 6.3VDC coming out of the right side of the board, and 7.2 VDC coming from the right/bottom side of the board

Left side - 1.2 VDC coming out from the left side, and 7.3 VDC from the left/bottom side of the board.

Is it possible that the LT1764 regulator is bad?

[Paul Birkeland]

Oh so you have good voltage out of the front DC pads, good to know!

Can you try disconnecting the green wires leaving the faulty side of the board to see if that voltage pops up?

[Yossihaimberg]

No change. Still reading 1.2 VDC

[Paul Birkeland]

On the bottom side of the PC board, the 1K and 237 ohm resistors poke through and there's a trace that connects them together.  If you set your meter to beep for continuity and touch one probe to each of those solder joints, do you have continuity between them? 

I'm thinking the regulator is totally fine but the traces on the PC board may not have survived the rework that was done.