In servicing this amp, Im not finding proper +-15vDC on preamp components. im unable to determine where to start actually. What components are responsible for housekeeping voltages?
The amp powers on and idles at 1.5A. No passing audio. Looks like the Class-D section and PS is ok
Thank you
The amp powers on and idles at 1.5A. No passing audio. Looks like the Class-D section and PS is ok
Thank you
I may have an issue with the yellow transformer near FET471. Its shorted across 3x pins per row not sure if that is right.
Those 0.22 ohm resistors seem to be ok. I removed that transformer and thats how I noticed legs 2-3-4 shorted and 6-7-8 shorted together.
That's normal. There should be two more shorted terminals. One is connected to B+. The other is connected to FET471. Those are the primary winding.
Did you see the MTX 81000 page?
repair_tutorial/miscellaneousstuff/mtx/mtx81000d/mtx81000dwaveformsandnotes.htm
That FET drives the yellow transformer. Feedback from the output of that transformer does allow it to regulate but it doesn't act like FET260 next to it (which is part of the regulator circuit for one of the optocouplers).
repair_tutorial/miscellaneousstuff/mtx/mtx81000d/mtx81000dwaveformsandnotes.htm
That FET drives the yellow transformer. Feedback from the output of that transformer does allow it to regulate but it doesn't act like FET260 next to it (which is part of the regulator circuit for one of the optocouplers).
Back looking at this and the MTX81000 page. Im finding the diodes just above the transformer are not regulating +-15vDC. Im getting +6vDC to the right of the right set, and -1vDC on the left of the left set. Most other readings with my scope are showing correctly from what I can tell to the 81000D page.
The 100uf SMD caps to the left of those diodes are getting quite warm, as is the 33ohm resistor to the left of the transformer.
D475 and D472 are acting 'shorted' or so as they appear to be connected to the 0.22ohm resistors south of the transformer.
Head scratcher
The 100uf SMD caps to the left of those diodes are getting quite warm, as is the 33ohm resistor to the left of the transformer.
D475 and D472 are acting 'shorted' or so as they appear to be connected to the 0.22ohm resistors south of the transformer.
Head scratcher
Did you remove the two diodes and the two capacitors to check them off of the board?
Is the inductor there open?
Are any op-amps heating up?
Is the inductor there open?
Are any op-amps heating up?
I've found D472 shorted. I replaced it with HER106 and the amp passes audio. Is this a suitable long term replacement?
It's definitely not ideal (lower current, higher forward voltage, slower). Unless this is your amp and you don't intend to sell it, I'd order the exact replacement.
Not out of the woods yet. I found a like rectifier on a parts MTX and installed it for further bench testing.
Under load, the amp immediately goes crazy with any kind of increased signal I cant even get the amp to pull more than 3.5A current before it goes berserk. Its not stable at all.
With no load, I can tell the output has a real problem. Heres a photo of my scope at 20v/Div, 1ms with a high voltage 75hz inputted sign wave. The bottom half of the output is messed up.
Under load, the amp immediately goes crazy with any kind of increased signal I cant even get the amp to pull more than 3.5A current before it goes berserk. Its not stable at all.
With no load, I can tell the output has a real problem. Heres a photo of my scope at 20v/Div, 1ms with a high voltage 75hz inputted sign wave. The bottom half of the output is messed up.
If you set the crossover to the highest frequency, does that make a difference?
DCV on the gate of the muting transistor?
Do you have clean audio on the input (pin 5) of the 5532 drive op-amp?
Do you have ~18v across the PS terminals of both optocouplers?
You may be the first person in history to see that page.
DCV on the gate of the muting transistor?
Do you have clean audio on the input (pin 5) of the 5532 drive op-amp?
Do you have ~18v across the PS terminals of both optocouplers?
You may be the first person in history to see that page.
Where is the muting transistor? What board denomination?
Yes clean audio on pin 5 of the 5532.
I have ~19v and ~21v on each Optocoupler power terminals.
Yes clean audio on pin 5 of the 5532.
I have ~19v and ~21v on each Optocoupler power terminals.