Dead Klipsch Promedia 5.1 THX

[procrastineer]

Hey everyone. I bought a “as is” Klipsch Promedia 5.1 speaker system from an auction site.

Before opening the back of the sub I tried turning it on few times and twice I heard a loud “thump”, most times it didn’t turn on at all. I used to have a Logitech z680 and have heard similar noise from sub when turning it on.

As many have pointed out I found documentation done by Dale Thompson at http://www.thompdale.com/bash_amplif...1_bash_amp.htm very useful.

With above documentation I verified that the Line filter is working fine by measuring 240V AC from T1 and T2 terminal of the Line Filter board.

The problem seems to be in the AC-DC converter board. It seems the R519 and R520 resistors on AC-DC board have become open circuits (checked with continuity checker on the multimeter). According to the schematics these two resistors should be "zero ohm" interconnecting links.

As you can see from the photo [http://imgur.com/KwW4l.jpg] only one resistor still in place is the R521 resistor.

Can someone with a working sub check that there is a connection on R520 and R519?

Thanks for any help.

[stpete cooling]

The problem is not with that section. Your photo shows the standard, correct connections. However, the photo does show that someone worked on the daughterboard next to those circles, and that board is prone to fail from heat. It was originally bright green. You could have a main relay problem, but as part of any repair I would go through and replace and upgrade the wattage of the 470 ohm (2, to 1 watt), plus the following 1% precision resistors: 205,000 ohm, 392 ohm (2) and 22 ohm (2) (to 1/4 watt). The precision resistors are prone to fail or change values, causing problems. Without seeing the panel, though, there is no way to be certain what the cause is.

[procrastineer]

Thanks, I figured out that the resistor combination that I mentioned in the first post varies depending on the 120V (US) and 230V (rest of the world?) mains supply.

How do you know that someone worked on the daughter board? I'm guessing from the different color of the board?

I am considering replacing the susceptible components in the daughterboard but it looks like I have to unsolder the daughter board first as it is really close to the transformer on the AC-DC converter board. This is rather difficult since daughter board has eight pins.

[stpete cooling]

I could tell someone had worked on it because there is a small yellow piece of insulation (not original) at the bottom of the board. That is an area where the heat is the worst, and arcing eventually develops. Perhaps someone previously repaired that section.The daughterboard does need to be removed in order to replace more than the top part or two. A desoldering gun (like Hakko's 808?) or heating all pins simultaneously with a bar of solder-soaked braided wire can accomplish the removal. Based on that board's color, I'd replace all but the the HT-60 diac, the transistor, the 1.00 k 1% resistor and the two 1N3070 diodes (replacing the other 15 parts). Be careful with that board, the traces are very thin and easily damaged. When reinserting the board, be sure all 8 pins are back in circuit. If I can help, let me know.

[procrastineer]

Yes , the previous owner did say some work was done under

warranty.

I have removed the daughter board. When I was testing for

continuity to make sure that the daughter board PCB inserts (8 pin connector) are

not conducting due excess to solder from de-soldering, and I realized the PCB insert 6

and 7 is conducting. Could this be due to faulty Q2 (IRF 740)? Also PCB insert

1 and 4 is conducting for some reason? Only way I can see this happen is due to

transformer tap 6 and 7 shorting.

Thanks for your help.

[cityjim]

Don't have the schematic in front of me but aren't these speakers made for 120 volts? LIne filter filters the wall voltage/current. So you'd be talking about wall voltages. You shouldn't see 240 volts there. UNLESS there is some special 5.1 Ultras that can run on 240 volts. And if they are 120 volts then obviously plugging them into 240 volts might of caused the issue.

You don't check those 0 ohm resistors with the continuity feature. Use the ohm setting. Should read like you touched both leads together.

cityjim