Again needing help fixing Orion HCCA 225 Digital Reference

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Desolder one leg of the 270 ohm resistor in the attached image. Does that allow the voltage to go negative on the cap/100k resistor?
 

Attachments

  • P1010016x.jpg
    P1010016x.jpg
    403.1 KB · Views: 53
Pin 5 of that opto-coupler connects the negative voltage to the muting transistors. Something between there and the group of components near the muting transistors. Follow that trace (of which that pad with the yellow arrow is part) to see if you can find anything that doesn't look right.

Did the caps near that pad (yellow arrow) look original?

Is it possible that electrolyte could have penetrated the board (if the caps were replaced, previously)?

Be suspicious of any caps that the mute line trace passes under.
 
Last edited:
I replaced those caps when I posted on here the first time with problems with this amp. They were bad(bulging).

In following that trace I noticed spots of discoloration of the coating under those caps(see attached photos). Do you think that it could be electrolyte that penetrated the board as you were asking? I could see nothing else odd about the trace.
 

Attachments

  • 20180614_225236-1.jpg
    20180614_225236-1.jpg
    728.6 KB · Views: 53
  • 20180614_225254-2.jpg
    20180614_225254-2.jpg
    701.5 KB · Views: 40
Last edited:
Yes, the pad you indicated is going to a positive voltage. I monitored it for 15 minutes. Upon powering the amp up it was at +9.4v. It rapidly dropped to +3.6v from there it slowly dropped to +0.2v.



I didn't notice any damage to the trace under the rail caps when I replaced them. That doesn't mean it is not possibly damaged though.
 
I removed the caps. thoroughly cleaned the area. As I was cleaning some of the red coating came off the trace in question. I gently scraped the rest off and on each side of the trace as well. I thoroughly cleaned the area again and re-coated it. I reinstalled the cap and then checked the voltage on the pad, it was reading +12v. On a whim I reattached the resistor leg in the opto-coupler and again checked the voltage on the pad it was at -15v but with a few minutes of play it rose to 0.000v. I then took acetone and thoroughly wiped over the entire board. I tested it again and the voltage was at -17.5v but after a few minutes of play it rose to -2.5v. Seems I've successfully managed to make the circuit work in reverse!
 
It depends on how tired you are of it.

Although it's not the right way to do it, you could lift terminal 5 of the opto-coupler. Lift the mute resistors (I'll have a look to tell you which ones) and run a small wire between the opto and the resistors.

Another option would be to simply cut out the section of trace that runs under the caps and jump outside that bad area with a small wire.

If you use a wire as a jumper. apply a dot of adhesive at various points along it to make sure it doesn't break due to vibration.

How are the screw holes in the heatsink holding up?
 
Desolder the opto, pull pin 5 up and reinstall the opto-coupler.

Near the muting transistors, there is a 100k and a 2.7 ohm resistor that connect to the bad trace. They are near the cap marked 101. Lift those and solder them together. Run a wire from those to pin 5 of the opto-coupler.

That will remove the trace (but also a couple of other insignificant components).

If that works, you can connect a jumper as shown below. There are 3 cuts. This reconnects all components.
 

Attachments

  • DSCN1224x.jpg
    DSCN1224x.jpg
    590.1 KB · Views: 43
You can do it however you want as long as the section that's causing the problem is taken out of the circuit.

I don't quite understand what you intend to do but the replacement trace will probably have to be insulated from the board if the board has absorbed any electrolyte.

As a side note, the section that was bypassed on the amp I have here was still leaking voltage, even after cleaning the board. After being cut out of the circuit, it goes to +10v as soon as the amp powers up.

Whatever you do, realize that the via at one end of the bad trace is under the caps and has to be cut out. That's why I cut on each side of it and re-connected the components with the jumper.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.