Laney TT50H No Outout

[ca7922303]

Ok. I'll default to 120V AC line settings unless otherwise noted. On the midi board the is an IC called U2 that is a 74HCT08. If it is smaller surface mount type you will have to be extremely careful not to short any pins together. Measure DC volts at each pin and post results.

U2 has 14 legs. 12@2.7vdc, 1@18mv, 1@1.5mv. The 18mv is nearest to R50, 1.5mv is directly across from the 18mv, the 12-

[Enzo]

Oh my... ca, do you know how to count IC pins? Each pin does a specific job, and it isn't so useful just to know that several pins measure X volts. I'll try to explain, but really, just google "counting IC pins" and bunches of them show up. You start at the pin 1 corner. The IC might have a dot or a notch at the pin 1 end. Hold it so pin 1 is upper left corner. Now we count down that side and up the other. Look at your photo, U2 has a small white dot near the upper right corner. That is pin 1. Hard to see on that IC, but if you look to the left at U3, it also has the little dot for pin 1. Look close at that IC, and beneath the part you can see part of an outlne drawn on the board. Right next to the 3 number you can see a notch in the white outline. That notch also means pin 1 end.

SO look at U2. Pin 1 is upper right in the photo. Then we count along that side - going left in the photo - 2-3-4-5-6-7. Then on the lower side of the IC, we start at the lower left corner and count back up towards the pin 1 end. SO left to right we have 8-9-10-11-12-13-14

On a 74xxx series logic IC like that we usually find the negative power (or ground) connection at pin 7 and the positive supply at pin 14.

[ca7922303]

Oh my... ca, do you know how to count IC pins? Each pin does a specific job, and it isn't so useful just to know that several pins measure X volts. I'll try to explain, but really, just google "counting IC pins" and bunches of them show up. You start at the pin 1 corner. The IC might have a dot or a notch at the pin 1 end. Hold it so pin 1 is upper left corner. Now we count down that side and up the other. Look at your photo, U2 has a small white dot near the upper right corner. That is pin 1. Hard to see on that IC, but if you look to the left at U3, it also has the little dot for pin 1. Look close at that IC, and beneath the part you can see part of an outlne drawn on the board. Right next to the 3 number you can see a notch in the white outline. That notch also means pin 1 end.

SO look at U2. Pin 1 is upper right in the photo. Then we count along that side - going left in the photo - 2-3-4-5-6-7. Then on the lower side of the IC, we start at the lower left corner and count back up towards the pin 1 end. SO left to right we have 8-9-10-11-12-13-14

On a 74xxx series logic IC like that we usually find the negative power (or ground) connection at pin 7 and the positive supply at pin 14.

Didn't notice the dots on board. Used to seeing a notch on IC.
#1-2.7vdc
#2-2.7vdc
#3-2.7vdc
#4-2.7vdc
#5-2.7vdc
#6-2.7vdc
#7-1.5mvdc
#8-18mvdc
#9-2.7vdc
#10-2.7vdc
#11-2.7vdc
#12-2.7vdc
#13-2.7vdc
#14-2.7vdc

[g1]

Doesn't look like there are any power supply voltages there. Schematic shows pin7 grounded and pin14 should get +5V supply.

[ca7922303]

Doesn't look like there are any power supply voltages there. Schematic shows pin7 grounded and pin14 should get +5V supply.

Think I could disconnect that board or jump something to bypass midi board?

[g1]

Think I could disconnect that board or jump something to bypass midi board?

No. It's not just for midi. All the switching is controlled by that board.
But those measurements are not right. Maybe you were not getting a good ground with the black probe or something. Try and get to where you can measure 0 and +5 at pins 7 and 14.
I'm fairly sure that chip is at least partly working because you are able to switch between the master volumes at the left of the front panel. But to track down the problem we have to get good measurements at that chip.

[Enzo]

And leave us not assume there is continuity between pin 7 and whatever he is using as a ground for the meter.

[g1]

U6 is a 7805 regulator. See what you get for DC on it's pins.

[ca7922303]

U6 is a 7805 regulator. See what you get for DC on it's pins.

U6(4.6v/0.4mv/102mv)
currently no lights @ power on U2 pin#7 to ground is 0.0 ohms
U2 now is as follows:
#1(101.3mv)
#2(100.5mv)
#3(3.6mv)
#4(0.3mv)
#5(1.0mv)
#6(2.7mv)
#7(0.4mv)
#8(1.7mv)
#9(101.3mv)
#10(9.1mv)
#11(3.6mv)
#12(0.3mv)
#13(4.5mv)
#14(100.9 mv)

[ca7922303]

U6(4.6v/0.4mv/102mv)
currently no lights @ power on U2 pin#7 to ground is 0.0 ohms
U2 now is as follows:
#1(101.3mv)
#2(100.5mv)
#3(3.6mv)
#4(0.3mv)
#5(1.0mv)
#6(2.7mv)
#7(0.4mv)
#8(1.7mv)
#9(101.3mv)
#10(9.1mv)
#11(3.6mv)
#12(0.3mv)
#13(4.5mv)
#14(100.9 mv)

Correction: pin #7(-1.2mv)

[The Dude]

U2 voltages won't be right without the regulated 5V supply. You first need to figure out what's happening with your 5V. I'd first check resistance of the output leg of the regulator to ground and see if you have a short or near short on that rail.

[ca7922303]

U2 voltages won't be right without the regulated 5V supply. You first need to figure out what's happening with your 5V. I'd first check resistance of the output leg of the regulator to ground and see if you have a short or near short on that rail.

U2 pin#14 to ground (4.1 ohms)

[g1]

What happened? You must have had the 5V supply before when you could switch between vol.1 and vol.2 at left end, I guess that is not possible anymore?

[ca7922303]

What happened? You must have had the 5V supply before when you could switch between vol.1 and vol.2 at left end, I guess that is not possible anymore?

No lights lit up now. Don't know if there was ever 5v@ pin#8?What do you make of pin#8 to ground @ 4.1 ohms? Does that mean a short-U2?

[The Dude]

There is obviously a short (or near short) somewhere on the 5V line. You'll have to track it down. Since the supply side of the regulator is also quite low, my first suspect would be the regulator itself. I'd remove the regulator and see if the resistance reading on the rail is still low resistance.