Strange Voltages

[andrew7667]

No other wiring changes than the NFB and I took out the brightness switch. I currently have it hard-wired so that it's in the bright, but not very-bright setting.

I changed the layout a bit because I drilled wrong. The pots are wired reverse, but they're wired correctly according to the schem. The board is also facing the opposite way. Point x is still going to point y though and the board is the same.

The socket wiring is fine. I've checked all the wiring in the amp and it's checked out. The heater voltage is a bit high (6.9-7v depending on what's coming out of my wall), but the heaters all come on.

Edit: Yes, it's Dan's Rev. 3 layout.

[andrew7667]

I'm currently not with the amp, but I'll be sure to make a chart for you guys tomorrow.

If you guys need anything else (pics of certain spots, voltages at certain spots, etc.), let me know. I appreciate all the help I'm getting and I don't mind helping you help me.

[Schorsch]

Measure the resistance from Pin 3/8 to ground. There should be approx. 22-23k

Have you done this? What's the measured value?

[zaphod_phil]

Since this amp is an AX84 project, I'm wondering why it's being debugged on 18watt.com and not AX84.com. Yeah I know 18watt.com is a friendly crowd, but so is AX84.com, and you're more likely to find people with experience of this amp over there...

[andrew7667]

Phil, I've tried to find help over on AX84 several times. I've gotten one response total from someone telling me they used to live in El Paso. However, when I post over here, my question is almost always answered by people who give me a little more help (well, a lot more help, actually).

[andrew7667]

Measure the resistance from Pin 3/8 to ground. There should be approx. 22-23k

Have you done this? What's the measured value?

I was getting an open circuit and I also managed to get my DMM to read a little over 1m, but I think I was touching pin 7. I wasn't able to get a good, solid reading on the wire that connects pin 8 to the 470ohm resistor so I'm assuming it isn't able to find ground at all. Aha! So I see that there must be going on in the grounding like you all said earlier. I'll double check the wiring on my board in a moment. I apparently missed a wire, corrected...the amp now fires up. It's still reduced output (there's probably another wiring error), but it's tons louder than it was before. I'll go through, with the schematic, and make sure that EVERYTHING is connected properly. I'll also go through and redo my ground scheme to make things a little more quiet.

[Manoteal]

Andrew,
Glad to see you making progress with your amp. I knew that there had to be a ground up somewhere. Take your time and check across parts and then across the wires that connect the parts to make sure they are really connected. Solder is weird sometimes. I had a similar problem where I had no power at all and I looked and checked and looked some more and it turned out to be a bad solder joint on my screen resistor. With no voltage on the screen, I was getting nothing. I finally found it when I measured the far side ot the resistor to the socket itself and came up with an open. The joints looked good, but reheating it fixed it and I got my sound back. So check the parts (it is easy to put 150K instead of 1K5 for example) by measuring them, and you will find the problem when something doesn't measure right. Good luck!