Line 6 HD-147

[Enzo]

Forget this 50% stuff. If a 40v supply is sitting at 5mv or 10mv is irrelevant, it is not at 40. SOme tiny residual voltage doesn't matter if it changes by "50%."

If a SMPS tries to start but can't, there is often a small spike, which is enough to put a few millivolts or whatever into the filter caps.

Imagine you all come out to your car, and the tire is flat. Really flat. Now the rest of your family goes ahead and gets into the car. Your flat tire is now even 50% flatter. The important fact is that there is no air in the tire, not the dimension of the squished rubber.

[ricach]

Forget this 50% stuff. If a 40v supply is sitting at 5mv or 10mv is irrelevant, it is not at 40. SOme tiny residual voltage doesn't matter if it changes by "50%."

If a SMPS tries to start but can't, there is often a small spike, which is enough to put a few millivolts or whatever into the filter caps.

Imagine you all come out to your car, and the tire is flat. Really flat. Now the rest of your family goes ahead and gets into the car. Your flat tire is now even 50% flatter. The important fact is that there is no air in the tire, not the dimension of the squished rubber.

Enzo, I'm sure you'll agree that there are many circumstances where such 'little' things can help indicate where the problem might lie.

Patient: Doctor, it hurts worse when I do this....
Doctor: Then don't do that.

[Enzo]

Yes, of course, there are many times when tiny details matter. Not faulting you for being thorough. Just urging to put the data into the larger context.

[km6xz]

I am not happy working on Line 6 since I usually can't get parts and they are so flimsy that mechanical parts are often needed. I am not familiar with this amp because it was built soon after we stopped working on Line 6, being the first outside warranty station for them when the company started.
This is a case where many of the symptoms are good signs or bad, but telling the difference takes studying the schematic a bit. This amp has 2 independent power supplies as has been discussed. The high current power supply is either shut down, or not starting but the low level supply is working fine. When first turning it on, is there a pulsing in mains current, a small regular peak and drop of current draw?
For the complex fault detection circuit to run, it needs at least a short duration presence of supply voltage before it decides to shut down the power supply or shut off the gate drive to the output section. If there is a short in the secondary of T5 there will be a pulsing but a bit higher current. You should be able to see that with the scope on any point in on the secondary of T5. If there is no spike in current from cold start or pulsing while on, the inverter is not firing up at all so the problem is early in the primary of the larger power supply. There are shut down lines that give the signal to stop the power supply, pin 6 of Header 3. There is also a Sense pair coming from the Secondary of T6 going to Header 3 pins 1 and 2 that samples current through the primary of T5. readings of those points will tell you a lot, if it is trying to fire up or if the primary of T5 is just dead. If if it is just dead, there are only a few things that would prevent any current flow and those can checked with it unplugged from the wall and an ohm meter such as the primary of T5 being open, the power MOSFet driver bad etc. If you are seeing activity on pin6 of the header connector, the supply is being shut down for safety reasons. The power supply control circuit monitors all sorts of parameters and any one of them can trigger a fault: high temp, DC offset, high current in several different circuits, excess voltage in the secondary....
Try those listed first steps, all on the secondary side of T5 so you can measure with your scope ground clip on ground without blowing it up.

If it appears that the main supply is being shut down, it is not terribly difficult to figure out the sense trigger that is disliking what it sees.
If it is simply a shorted diode as Enzo pointed out, on the secondary of T5(very common, they lead a hard life) expect to see some pulsing of primary current.
Good luck.
By the way....did I mention that I HATE Line 6? When you buy one of their systems that connects to a computer, anything, they remotely control when and if you can use it, how many items at a time you can use, on which computer it can be used etc. I recommend everyone avoid Line 6 and buy real equipment.

[ricach]

Thanks for the suggestions. Unfortunately I have other pressing problems but will get back to this Line 6 soon. I really appreciate the time and thought that has been put into this issue by all. Thanks again.

[lbaudio]

Line 6 schematics

I downloaded the Elektrotanya one, I guess it's the same as yours.
You posted the "secondary power section" on page 11.
Just to its left is "primary power section" which turns 120VAC into +/-170V rails for the switcher (Q3/4/5/6) which are transformer driven through T3b/c secondaries.
Find where T3a sits and who's driving it (I got tired searching).
Anyway I still find it a little too much for home repair.
Even official service shops find them tough .

Hi Juan,
Any chance of getting a copy of the schematics? They're not available on Elektrotanya any longer.

Thanks,
Ken

[J M Fahey]

I'll check, *maybe* it's on my other computer.
If so, it's yours

EDIT: sorry, it's not there.
I generally download >>SS<< guitar amp schematics, much harder to find than the ubiquitous tube ones, but I must have erased this one since the switching PSU and digital preamp made it useless for me.
Sorry.

[lbaudio]

I'll check, *maybe* it's on my other computer.
If so, it's yours

EDIT: sorry, it's not there.
I generally download >>SS<< guitar amp schematics, much harder to find than the ubiquitous tube ones, but I must have erased this one since the switching PSU and digital preamp made it useless for me.
Sorry.

OK, thanks, anyway.