trinityamps.com

Found another 1 meg pot (measures just under 1 meg) and installed it. Reconnected the VRM.
Back to where I started. Low volume, and the following voltages:

All controls at max. Mains 121.9 VAC. B+ 441
(target voltages in brackets):
C12 (400): 83VDC
V2 pin 8 (29) : 4.8V
C6 (340) : 70V
V1 pin 7 (191) : 40V
V1 pin 1 (203) : 44V
V1 pin 3 (2.3) : 0.3V
V1 pin 8 (1.7) : 0.3V

_________________
This way to the unanswered questions -->
<-- This way to the unquestioned answers

All the resistors measure to spec?

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I'll have to start measuring. If I understand correctly, a resistor must be disconnected from the circuit to test it? Would lifting one leg do it?

_________________
This way to the unanswered questions -->
<-- This way to the unquestioned answers

If would but you might find you don't have to. Measure in place and if they are correct, move to the next one. Solid state are different

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Went ahead and pulled one leg of the resistors around the VRM (R20 to 23). I measure:
R20 (5R) : 5.4R
R21 (100K) : 100.2K
R22 (100K) : 98.9K
R23 (100R) : 98R

Is R20 OK?

Subsequently measured the rest of the resistors in place. The only ones that appear out of spec are:
R18 (22K): 2.4K
R5 (220K): 150K
Both are on the Tweed/Tude switch.
Are either if these likely culprits?

Since bypassing the VRM earlier seemed to restore voltages, does this not point at the MOSFET?

_________________
This way to the unanswered questions -->
<-- This way to the unquestioned answers

R18 is way out, it would not cause the problem but I would pull one leg off and retest, then replace.
You can test the Zener by measuring the resistance in both directions by reversing the test leads. One way should be very high, the other way low. You will probably have to pull on leg as well. If that is all good, then yes, the MOSFET is the prime suspect.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

R18 is OK.

With one leg disconnected, diodes D1 and D2 measure zero resistance in one direction, and with test leads reversed one is 14K and the other 88K (not sure which is which).

I guess I'm going to need a new MOSFET. Does it make sense to replace the diodes as well?
I'll take a control pot too as the one I found locally was pull-on rather than rotate.
What's the cost including shipping?

_________________
This way to the unanswered questions -->
<-- This way to the unquestioned answers

Diode sounds odd. I was expecting low and vey high (Megs or infinite) the opposite direction.
Shoot me an email. Shipping is as expensive as the parts if you want a pot. If just a MOSFET and diode it's cheap. Just the way canada post charges us. A1 sells a switched pot if you are going by. I would have thought you could get the correct pot locally.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

The struggle continues....

Installed the new MOSFET and diode. Volume has returned, but VRM is non functional. Voltage does not change when turning pot.

Here are my voltages now:
All controls at max. Mains 120.7 VAC
(target voltages in brackets):
C13 : 418
C12 (400): 410VDC
V2 pin 8 (29) : 28V
C6 (340) : 342V
V1 pin 7 (191) : 182V
V1 pin 1 (203) : 194V
V1 pin 3 (2.3) : 1.8V
V1 pin 8 (1.7) : 1.6V

_________________
This way to the unanswered questions -->
<-- This way to the unquestioned answers

Diode in the correct way?. All control wires have continuity!

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Any chance of some clear pics of the board and general wiring of the amp, especially around the VRM and Diodes etc? With pics sometimes something will pop out as not right. Or has this been fixed by now? It's always good to wrap these threads up with a documented fix.

Agreed, that's the way it should end!

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

VRM still not functioning.
Here's a pic of the diode
[url][URL=http://s474.photobucket.com/user/jharasympho/media/Trampdiode_zpsd29ca943.jpg.html][/url][/url]

_________________
This way to the unanswered questions -->
<-- This way to the unquestioned answers

Everything seems to be pointing the right way from what the pic shows, have you tried reflowing all the solder joint's and then tested continuity of each as you are working on it? Working from the schematic and cross off each connection as it is attended to and checked as good.

Failing that it looks like you are in Ontario same as Trinity, if it were me at this point after having the amp not working properly for a couple of months after completion I'd consider biting the bullet on some postage and diagnosis/fix and send the amp or drive it over and drop it off to Stephen for some bench time.

Might be an easy fix for kurtlives (Chris) and he is in Toronto. Of course, I would be happy to get it going as well.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps