Laney TT50H No Outout

[g1]

Post 3 contains the link to the service manual. Everything except a picture is included, even those connectors that is the main issue with most problems.

From what I can see there is no schematic showing any power tubes (EL34) or the power amp section in that service manual.

[Jon Snell]

As Loud Tech do not pass too much information on and produce Chinesium schematics, the TT50 manual is a cross between schematics and layout drawings. It is fairly easy to see what is missing from the two clips attached and work out how the output section and transformer is wired.
Hope that helps.

[ca7922303]

So, i've replaced R43, it was burnt and had to epoxy the hole in the board undernearth it. Using variac up to about 60 volts, I get about 200v & 60v on R43. Still only able to get a very faint signal only when plugged into return Jack. All ribbon cables are good, can't find any resistors not reading correct. Any ideas on this one? Thanks.

[Jazz P Bass]

You need to narrow down what is what.
Where does the signal fail?
Here is the block diagram.
Do the Record & Line out jacks work in to another amp?

[ca7922303]

Yes, have good clean signal record out/line out to another amp previously mentioned before finding R43/board burnt. Have not checked since replacing R43. Trying to find bad parts under main board be before putting back together.

[ca7922303]

You said here is the block diagram? I don't see it. I've got the service manual if your referring to it.

[g1]

You said here is the block diagram? I don't see it.

Go to your 'user settings' and click on the 'account' tab. Scroll down to 'conversation details' and select 'posts' instead of 'latest activity'.
That way you will be able to see all of the attachments.

[Jazz P Bass]

If the Line Out is good then that leads you to the output section.
It goes into the phase inverter tube,
At the output tubes check the Volts ac signal at the grids (pin 5).

Note: unfortunately the output section schematic is drawn strange.
But it IS all there.

The Line Out (I assume) can be used as a Power Amp in if need be.

[ca7922303]

-15v on V7 & V8 pin#5 @ 60v on variac. R43 is 210v & 70v.

[ca7922303]

Went to 100v on variac, V7/V8 @ -25v, smell epoxy and see smoke, R43 @ 337v & 0v. R43 now OL resistance.

[Enzo]

You really shouldn't variac til it smokes. That is counter to the point. One should monitor mains current, and as we dial up the variac, watch the current, and if it starts to rise, STOP right there.

[Jon Snell]

If R43 fails then there is an issue with just that part of the power supply.
There is only one component that can fail and that is C37. There are no other components that can draw enough current to ground.
V3 may have an issue but I would have thought it would have been obvious.
Of course it could be fiddling error causing a short circuit on a fixing point ... can't physically see the amp so just a guess. (Must get a new crystal ball).
Keep logical and think about the voltage path.

[ca7922303]

I'm going to remove the board and pull R43 this evening after I get off work and get readings on C37, V3.. Thanks for your help

[ca7922303]

C37 will charge to 013 @ 2000k ohms and then @ 0.3 - 0.0 @ 200mv. R43 is of course OL. C23 charges to OL and discharges from 195 to 0, r35,36,37,38 all good, C17 is 184 @ 2000k ohms, C18 is 352 @ 2000k ohms, R39&41 good, R40&42 read 010 @ 2000k ohms, C21 charges to OL @ 2000k ohms, discharges to 0.0 @ 200mv, C20 stays at 048 @ 2000k ohms, no discharge @ 200mv. Not finding C19? Are R43, C37, C20, R40, and ,R42 possibly bad? I checked everything in the schematic that is connected to R43. Appreciate any help.

[ca7922303]

C19 is 375 @ 2000k ohms.