First time #183 Build

[MusicMaker]

You can only see the static current when setting idle bias, and being within a few mA is close enough. I would swap V4 and V7 to get the total current on each side a little closer to matching, set the average current to ~37 mA and call it good. You have the ability to adjust the dynamic balance with the PI trimmer pot, which you can play with later.

Swapped

Did anything change when you added the missing jumpers to the switches (I assume Mid-Boost and Rock/Jazz)? Which controls are working or not working now?

No change.

See if the resistance from the volume pot wiper to ground varies as you turn the volume knob.]/quote]
Yes. It goes from zero to 868 ohms. (0-10 respectively).

Confirm that the relays are working by measuring resistance across the common and NO or NC pins with the back panel switches in both positions (foot switch not connected). The pins along each side are coil, common, NC, NO. You only need main power on to do this.

I think we found the problem!

PAB does not change from 12vdc, though you can hear the relay click when lightly lifting the switch.

I did swap them out a few days ago to see if the PAB would work, but it did not.

That's the same board where, if you flipped the amp over it would fall out! I flashed the leads with some solder to tighten it up, but apparently the socket is bad.

Fortunately, I have a spare socket to dump in there. Kind of a PITA to do, but I've done it before for IC's....

I shall return to let you know the results!

[martin manning]

It goes from zero to 868 ohms. (0-10 respectively).

Seems low... maybe it's 868k ohms (almost 1Meg)?

[MusicMaker]

Swapped out the socket to be sure.

Volume or switches still don't do anything... crap!

Not sure where to go from here.

[MusicMaker]

It goes from zero to 868 ohms. (0-10 respectively).

Seems low... maybe it's 868k ohms (almost 1Meg)?

Yeah, forgot the "K"

Going to be out of town this weekend. Revisit on Monday...

[rogb]

Swapped out the socket to be sure.

Volume or switches still don't do anything... crap!

Not sure where to go from here.

You need to start at the input jacks and sweep right across the front panel, checking ALL wiring and grounds, jumpers etc to all sockets, jacks,, switches and pots. When you have double-checked them, tick it on your layout. Do the same for the relays.
Then do the same for the back panel. switches and send/return sockets.

[norburybrook]

Have you got your diode's the right way round on the relay boards? Mine were confusing as the actual graphics on the top of the relay said 'as seen from below' which mean everything was actually the reverse of the what it looked like..... if you see what I mean..... so my diodes were the wrong way round.



Just a thought


Martin helped me sort through this one too.


Marcus

[martin manning]

Looks like the relay coils are non-polarized, and the diodes are oriented correctly. I would hope so, since these boards were pre-assembled in the kit! However, the relay PCB's are not the same as the boards shown in the layout drawing. I can't see where the contact traces connect in the photos above so I can't tell if they are wired properly or not.

Do you have any additional documentation that shows the relay PCB connections?

[MusicMaker]

Looks like the relay coils are non-polarized, and the diodes are oriented correctly. I would hope so, since these boards were pre-assembled in the kit!
However, the relay PCB's are not the same as the boards shown in the layout drawing. I can't see where the contact traces connect in the photos above so I can't tell if they are wired properly or not.

Do you have any additional documentation that shows the relay PCB connections?

Finally got some time to dig into the amp again. You are correct about the boards not being the same!

See pics. However, the scheme isn't what the relay board does.
I pinned them out and the red arrows go to the same locations.

If I were to wire it as shown in the scheme w red wire in lower right corner it would go to the lower right pin and NOT to the 3rd from left on the back row.
That's why I wired the red wire where I did.

All the rest of the pinouts go to where indicated.

[martin manning]

What about this jumper?

[MusicMaker]

Swapped out the socket to be sure.

Volume or switches still don't do anything... crap!

Not sure where to go from here.

You need to start at the input jacks and sweep right across the front panel, checking ALL wiring and grounds, jumpers etc to all sockets, jacks,, switches and pots. When you have double-checked them, tick it on your layout. Do the same for the relays.
Then do the same for the back panel. switches and send/return sockets.

Pretty much have been through all that. Even rewired the OD & PAD switches.

If my understanding is correct... volume (first knob) controls V1p7.
(NOTE it's actually pin2, Nik's layout is backwards to the "100W in the style of #183" scheme - see pic)
When the 1M pot is at zero it takes pin7 (grid) to ground. No sound should get through after that point, yet it does.

I measured ohms with volume at zero to chassis and it indeed is zero.

I also checked from volume knob (center pin) to V1p7 and there is 220K ohms.
Which makes sense being there's a 220K ohm resistor in line.

Turning the volume pot to 10, I get 886K ohms (not quite a 1M ohm pot, though before installing I measured 899K ohms).

Why sending V1p7 to ground has no effect on the sound when it really should is a mystery. It's acting as if the pot wasn't in the ckt...

It also takes out the Bass, Mid, Treble which are all located in the general area.

The PAB relay is right in the middle of all this. I swapped relays to test them and the same result. Assumption is both relays are good.

I could burn some relay boards ala TAlbany's layout. I have some acid etch from several years ago and I could find some copper clad at the junkyard, but I'd like to understand what the problem is before doing that.

[MusicMaker]

What about this jumper?

That has continuity - from the red wire through both points.

Also this is the clean/OD relay no? I have OD.

I would think it was before it gets out of V1??


Here's the schematic I'm referring to so we're on the same page.
V1 is actually flipped on Nik's. See pic

So,
pin8 = pin3
pin7 = pin2
pin6 = pin1

[martin manning]

So you have both clean and OD now, meaning the back panel or foot switch noticeably changes the tone, and the OD trim, ratio, and level controls all work in OD? But in either mode the volume pot does nothing?

You should be able to silence the amp with the volume pot in clean or OD mode, and all that is required there is that the pot wiper can ground the clean 2 input.

[MusicMaker]

So you have both clean and OD now, meaning the back panel or foot switch noticeably changes the tone, and the OD trim, ratio, and level controls all work in OD? But in either mode the volume pot does nothing?

You should be able to silence the amp with the volume pot in clean or OD mode, and all that is required there is that the pot wiper can ground the clean 2 input.

Yes, I get OD and when I turn it off there is 'clean', but no volume, treble, mids, nor bass controls. No PAB w switch or stomp box, but relay clicks.

[martin manning]

Volume should work in OD too, and doesn't depend on the tone controls. Maybe solve that first.