So, on R101 to u2 pin 13 i have:
298.7k from the top leg
205.9k from the bottom leg
R101 measures 4.575k on circuit its supposed to be 4.7k
298.7k from the top leg
205.9k from the bottom leg
R101 measures 4.575k on circuit its supposed to be 4.7k
Doesn't pin 13 connect to the Q101 base with R101 directly?
The resistor value isn't an issue here if that's what it reads.
The resistor value isn't an issue here if that's what it reads.
Yes, it goes to the other side of the board tru diode 211 that sits by the 339. In series to this at the diode is r248 that connects to pin8 of u2.
I had another question. I’ve read most of the mtx treads that i can find, and rear something about an issue that is the lose ground, they could try to ground tru the rca. I’m thinking about this, because i traced the remote line, and as far as i can tell it goes up tru variyos diodes and transistors to near the u1 339, but then branches down to the rca shields. But it stops at d1 by the rca’s. R6 is no there to complete this line, and there’s solder on the pads, which leads me to think that it was there at some point. Is this the circuit that checks for dc at the rca’s that i’m looking at? Or am i losing my mind probing things. I do this quite often, i’ll start probing, and once i get to the other side of the board, i don’t even know why i was probing that.
Any tips on dealing with undocumented circuits like this for the first time? Should i draw the schematic as i uncover it?
Any tips on dealing with undocumented circuits like this for the first time? Should i draw the schematic as i uncover it?
Recheck. There should be no diode in the path between an output/control pin of either LM339 and the base of Q101. There should be only a resistor. Maybe pin 13 of U2 isn't the control terminal.
Ok, so i double checked, and the base of q 101 goes to r102, also goes to the emitter. On the base side of r102 i have r 101 that goes to a via and from there it is connected to pins 13 and 13 of u203. That is the other 339, closer to the rail caps. I have no idea why i was calling them u1 and u2.
Yes 13 and 14.
Here are the voltages for u203
339 (u1)
Pin 1: 0.496
Pin 2: 4.769
Pin 3: 10.420
Pin 4: 0.570
Pin 5: 3.19
Pin 6: 0.945
Pin 7: 3.191
Pin 8: 3.281
Pin 9: 5.00
Pin 10: 5.00
Pin 11: 6.562
Pin 12: 0.003
Pin 13: 0.670
Pin 14: 0.683
Here are the voltages for u203
339 (u1)
Pin 1: 0.496
Pin 2: 4.769
Pin 3: 10.420
Pin 4: 0.570
Pin 5: 3.19
Pin 6: 0.945
Pin 7: 3.191
Pin 8: 3.281
Pin 9: 5.00
Pin 10: 5.00
Pin 11: 6.562
Pin 12: 0.003
Pin 13: 0.670
Pin 14: 0.683
The amp is likely in protect.
Why is the inductor out of the amp?
Does the LED go green with it in the circuit?
Why is the inductor out of the amp?
Does the LED go green with it in the circuit?
I pulled the inductor due to there was a burned area on one of the legs. And there’s a blown cap right by it. I pulled it to check the burned section of the board for conductivity. The protect part, i’ve been considering it. The light right now is kind of greenish looking, but i can’t call it a solid green. I had the inductor in there last night(not soldered) and still the same. I checked the thermistors and the little inductors by the transformer and the output inductor and i got 5v on one side and 1.2v on the other of all of them. I shorted them to see uf i could get the amp to go into protect with the red light and no luck. I was able to get the red light to come on by removing diode d2. I’ll go ahead and get that inductor and that capacitor in there to see if anything changes. That was the only physical damage that i saw on the amp when i got it.
Is is possible for the light to be both red and green at the same time? Because this one looks green to orange depending the angle you look at it. I measured it and both cathodes(outside legs) are giving me 9.5v. The led leaking voltage? Let me take it off and see what it says.
It's possible for both to be lit. It's odd to have 9v on the terminals unless the other terminal is well above ground or unless the LED isn't a pure LED and has series resistors in the body of the resistor housing.
So i took the led off and put it at the top of the board and got a solid green connected like it came off, and solid red if i inverted it. I put it back on the other side if the board and it looks mainly green, but has some orange to it. Maybe my eyes are failing me.
Maybe a prior owner flipped the led to sell it so it shows green when is in protect. Seen it before. Lol. This one is going to be a tough one.
Maybe a prior owner flipped the led to sell it so it shows green when is in protect. Seen it before. Lol. This one is going to be a tough one.
I ment rotate the led so the green terminal is in place of the red and vice versa. It is possible for the damaged via, since the led is the only thing pocking out on the back side of the board. I’ve been sitting the board on a roll of tape so i don’t crush the led.
Mr perry, i have been doing research on different mtx amps. I’m still iffy about the missing components on my board. Mainly the transistor Q214 and some components around it. My other amps have it, and i came across this thread were q214 is responsible for switching the 494 and other op amps. Do you have any pictures of similar mtx amps?
Here is that thread.
MTX TA7801/TE1501D power supply issues.
Thank you for your time.
Here is that thread.
MTX TA7801/TE1501D power supply issues.
Thank you for your time.
The 494 is controlled by the voltage on the DT terminal. It always has power in some of the MTX amps. Didn't your start producing drive when you removed Q101?
Here’s one pic i found on this forum from another mtx and i noticed that the same components seem to be missing, except the ones i mentioned above. I do have another 2 amps that i can borrow parts from if this circuit is necessary. What do you think?
