Laney TT50H No Outout

[ca7922303]

Also, see burn marks at HT which reads (-236vdc), left fuse pin reads(-452vdc)right fuse pin(0.0vdc) all three(3) grid pins read(-39vdc)

[ca7922303]

R13 burnt. R13 is a pullup for pin 4 of U2. Pin 4 of U2 also connects to a pin on the 15 pin "switches" connector. SK3 pin 14. I suspect something bad happened in the switches and burnt up that resistor and likely damaged U2.

SInce R13 pulls up to +5 and U2 is powered by +5, that might explain the dead 5v regulator U6. WIth U6 removed, does +12v appear on the input pin connection?

12v does not appear on any of the SK3 pins at this point.

[Enzo]

Schematic does not call for 12v on SK3. I apologize for lack of clarity. I meant with U6 removed, does 12v appear at the input pin of U6? In other words, with the bad part removed, was the 12v supply reaching the point where U6 had been. Look at your schematic. U6 is a 5v regulator. It has 12v coming into it, and it spits out 5v on its other side.

[ca7922303]

Schematic does not call for 12v on SK3. I apologize for lack of clarity. I meant with U6 removed, does 12v appear at the input pin of U6? In other words, with the bad part removed, was the 12v supply reaching the point where U6 had been. Look at your schematic. U6 is a 5v regulator. It has 12v coming into it, and it spits out 5v on its other side.

U6(4.6vdc/0.4mvdc/102mvdc)

[g1]

U6(4.6vdc/0.4mvdc/102mvdc)

That is at the board pins with the part removed? If not, remove and re-check.
If part was already removed, find R43 on midi board. Measure voltage at each end of it.

[Enzo]

SO with no 12v in, even a good one couldn't produce 5v. Look at your schematic. U6 received +12v through the 5 watt resistor R43. Find it, is there 12v on at least one end? With no U6 there SHOULD be 12v on both ends. If so, then move to D6. Is there 12v on its anode? And if so then on its cathode?

[ca7922303]

That is at the board pins with the part removed? If not, remove and re-check.
If part was already removed, find R43 on midi board. Measure voltage at each end of it.

I was showing R43 on main board, it no longer has +442vdc or any of the preamp tubes pins 1 & 6. But I will check R43 & D6 on midi board and post results.

[ca7922303]

That is at the board pins with the part removed? If not, remove and re-check.
If part was already removed, find R43 on midi board. Measure voltage at each end of it.

R43(0.1/0.1mvdc)
D6(14vdc/0.2mvdc)
R43 resistance(329.8 ohms)

[ca7922303]

That is at the board pins with the part removed? If not, remove and re-check.
If part was already removed, find R43 on midi board. Measure voltage at each end of it.

1st measurements were with U6 reinstalled, these are with U6 removed:
R43(14/14vdc)
D6(14/14vdc)

[ca7922303]

U6(4.6vdc/0.4mvdc/102mvdc)

Also, with U6 removed14vdc/0.0mvdc/0.0mvdc)

[g1]

Those are good results, means resistor and diode are ok.
Leave U6 removed. Measure resistance from U6 pin 3 pad on board to ground.

[ca7922303]

Those are good results, means resistor and diode are ok.
Leave U6 removed. Measure resistance from U6 pin 3 pad on board to ground.

U6 removed, pin#3 pad on board to ground (51 ohms)

[g1]

See if you can de-solder pin14 of U2, til the pin moves freely and is no longer touching the pad. Be careful as the traces can be easily damaged and are thru-hole because it is double sided board. Then re-check that resistance of U6 pin3 pad to ground.
If you have very fine side cutters, I would just sacrifice U2 anyway. It's a lot easier to remove the pins if you snip them all and then desolder them one at a time pulling them out with needlenose. We know U2 took a hit because that resistor R15 is fried. And you also need to replace that regulator U6.
So that's U2, U6, and R15 to replace.

[ca7922303]

See if you can de-solder pin14 of U2, til the pin moves freely and is no longer touching the pad. Be careful as the traces can be easily damaged and are thru-hole because it is double sided board. Then re-check that resistance of U6 pin3 pad to ground.
If you have very fine side cutters, I would just sacrifice U2 anyway. It's a lot easier to remove the pins if you snip them all and then desolder them one at a time pulling them out with needlenose. We know U2 took a hit because that resistor R15 is fried. And you also need to replace that regulator U6.
So that's U2, U6, and R15 to replace.

Is it R15 or R13 that is burnt, I was thinking from looking at the board that it went from left to right 11,13,15,17?

[ca7922303]

See if you can de-solder pin14 of U2, til the pin moves freely and is no longer touching the pad. Be careful as the traces can be easily damaged and are thru-hole because it is double sided board. Then re-check that resistance of U6 pin3 pad to ground.
If you have very fine side cutters, I would just sacrifice U2 anyway. It's a lot easier to remove the pins if you snip them all and then desolder them one at a time pulling them out with needlenose. We know U2 took a hit because that resistor R15 is fried. And you also need to replace that regulator U6.
So that's U2, U6, and R15 to replace.

With U2 pin #14 cut from touching board, U6 pin#3 pad to ground is (37.5 ohms).