Orion HCCA 2100 no rail voltage.

[Perry Babin]

Is the drive still weak on the hot side?

 

[Chopperbuilder]

Dive has evened out on both sides.

 

[Perry Babin]

When you stated that the PS FETs were 'still' heating. I assumed that it was only one side. Is that still true?

How much current is the amp drawing at idle?

 

[Chopperbuilder]

Yes only the left side is heating up.

Through the choke it was drawing 2.2 amps at idle. Without the choke my meter showed 22 amps before it blew the fuse in my meter. Same thing happened back when I tried doing a current draw test on the HCCA 225.

 

[Perry Babin]

What are you referring to as a 'choke'?

A choke is a coil/inductor.

Have you tried leaving your scope on longer? I seemed to work better after being powered up for a while.

 

[Chopperbuilder]

What I am calling a "choke" is the resistors I am using between the power supply and amp to choke down the power to the amp.


I'll turn on scope and let it run but had it on for a while last night and it didn't make a difference.

 

[Chopperbuilder]

I was wrong about it being only the left side FET's getting hot the upper group on the right side is heating up too. The group of FET's I have outlined in the attached photo is the only set that is NOT heating up.

 

[Perry Babin]

Is the drive for the cool bank the same as the others?

Are the rail voltages all equal? Under a light load and at idle?

 

[Chopperbuilder]

After a while of messing with it this is the best the scope will do... I cannot get rid of the ghost image on the screen as seen in the photos.



Scope set at 2v/div and 20us


I numbered the top right of each photo to the corresponding set of PS FET's


Oddly enough the set of FET's that is the set NOT getting hot(#2 in the photo) is the set with the distorted wave form.

 

[Perry Babin]

They may not be getting hot because they're not being driven hard enough to be driven on.

The first photo looks like the PNP driver's 10 ohm collector resistor may be out of tolerance.

 

[Chopperbuilder]

Will you please point out the 10 Ohm collector resistor you are referring to?

 

[Perry Babin]

I can't tell which one it is on the photos I have. Find the MPSA06/56 driver pair. Measure the resistance from the collector of the A56 to the 3rd leg of the PS FETs. All 4 driver pairs should read 10 ohms between the A56 collector and ground (3rd leg of FETs).

 

[Chopperbuilder]

All are reading exactly 10 ohms.

 

[Perry Babin]

It doesn't look like it's going as close to ground as it should. If they read 10 ohms, check the collectors of all of the MPSA06 drivers. Do all read about the same voltage?

 

[Chopperbuilder]

I'll check the collectors now.

Just checked the DC voltage on pins 9 and 10 of the 494 again.
Pin 9. +1.943v
Pin 10.+2.758v

 

[Chopperbuilder]

See attached photo for the voltage of the collectors of all of the MPSA06 drivers.

 

[Perry Babin]

What happened to change the identical voltages on 9/10 to being so different?

Post photos of the signals on pins 9 and 10.

 

[Chopperbuilder]

My guess is there is something in that circuit that is intermittently failing.



The first photo is of pin 9.

Second photo is of pin 10.

 

[Perry Babin]

Did you align the trace with the reference before taking the photos? This is very important.

What is the voltage on pins 11 and 8 of the 494.

 

[Chopperbuilder]

Not sure what you mean by "align the trace with the reference". So the answer to your question is likely, no I did not.