Laney TT50H No Outout

[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.

[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]

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

[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

[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]

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-

[g1]

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.

[ca7922303]

Is there any time that the channel select buttons work?
Has this switching problem always been there or did it start up some time during the repair?

Got it like this, and no they have never functioned. The only thing I've observed is that depending on what voltage the Variac is set at, will light up the switches but they do not work. I way say that the two volume switches to the left that you asked about has a volume 1/volume 2 switch that does switch between those two at full power. I realize that the half power doesn't tell you anything, but trying to make any observations I can to pass on. Thanks.

[Enzo]

Running the amp at 60v really doesn't tell us anything useful.

[g1]

Turned Variac to 60v and channel 3 light goes out and number 1 & 2 light up. Have signal on channel 1 with fx mix @ zero, channel 2 has a hum which increases as volume and gain controls are turned up. Channel 3, which now light will not come on when pushed is non functional. Only signal I can get at full power, is thru return fx.

Is there any time that the channel select buttons work?
Has this switching problem always been there or did it start up some time during the repair?

[ca7922303]

One of the two volumes near the left end of amp.

The two volumes near left end both work when at full power and plugged into return fx jack. Can switch between the two. Channel 1 at left end works with channel 1 volume on right end of amp at 60v with signal plugged into instrument jack. Channel 3 does not work at all and channel two has a hum which increases with gain and volume controls turned up while at 60v with signal into instrument jack.

[ca7922303]

Do you mean one of the 2 volumes near the left end of the amp? Or do you mean Ch.3 master?

One of the two volumes near the left end of amp.

[ca7922303]

When you are using the instrument input (not FX return) you have to turn the FX mix down to zero. Have you tried that?

Tried fx mix @ zero with amp at full power and has no effect. Turned Variac to 60v and channel 3 light goes out and number 1 & 2 light up. Have signal on channel 1 with fx mix @ zero, channel 2 has a hum which increases as volume and gain controls are turned up. Channel 3, which now light will not come on when pushed is non functional. Only signal I can get at full power, is thru return fx.

[g1]

Channel 3 volume works on signal when signal is run into return fx.

Do you mean one of the 2 volumes near the left end of the amp? Or do you mean Ch.3 master?

[ca7922303]

When you are using the instrument input (not FX return) you have to turn the FX mix down to zero. Have you tried that?

Tried fx mix @ zero with amp at full power and has no effect. Turned Variac to 60v and channel 3 light goes out and number 1 & 2 light up. Have signal on channel 1 with fx mix @ zero, channel 2 has a hum which increases as volume and gain controls are turned up. Channel 3, which now light will not come on when pushed is non functional. Only signal I can get at full power, is thru return fx.