Needed help with repair PA amplifier

[Patryk754]

Hi, I recently managed to buy a Hollywood Impact 1000 amplifier at a bargain price. The seller informed me that one of the channels was damaged and was generating noise. However, after connecting the speakers and the signal, it turned out that the noise was present on both channels.

To solve the problem, I replaced almost all the capacitors with new ones, except for the two largest ones (10,000uF 80v) and both potentiometers, but the changes did not bring any improvement. After checking, it turns out that there is a connection between the plus and minus of the speaker output (right channel 0.505M ohm, left 0.47M ohm) I also replaced one relay because the old one was blocked and did not switch. Noise and interference are audible regardless of the song being played, the signal source (computer, phone) or the streaming platform (Spotify, YouTube). I have STX F360n speakers connected to the amplifier, and the problem manifests itself in a specific noise or interference that is clearly audible from the tweeters at different frequencies, they are not constant, but occur during music playback. For comparison, when I connect the same speakers to the Pioneer VSX 527 amplifier, the sound on the same paths is clean and free from interference, although it offers too little power for the speakers and my needs. In addition, I carried out the test on several signal cables, so they are not the cause of the problem. Below I put links to videos showing this problem

 

[nightstereo]

Please don't keep replacing random components hoping it will fix the issue. It's more likely you'll create new problems this way. The unit needs proper troubleshooting to determine its problem, I personally do not hear any distortion.

 

[gadget73]

Can you post a schematic?

Do you have an oscilloscope ?

 

[nightstereo]

Can you post a schematic?

Do you have an oscilloscope ?

There are no schematics available for these amplifiers anymore. It's a rare brand, not priceless, just rare. Yes, i have several oscilloscopes and can perform any measurements needed

 

[gadget73]

Thats going to make it harder but i suppose just hooking up the scope to see exactly what its doing is a first step

I own rare, worthless, and difficult to fix things myself. It gets exhausting becoming a subject matter expert on things nobody in the world is interested in.

 

[nightstereo]

Thats going to make it harder but i suppose just hooking up the scope to see exactly what its doing is a first step

I own rare, worthless, and difficult to fix things myself. It gets exhausting becoming a subject matter expert on things nobody in the world is interested in.

Where would you like me to monitor? the differential inputs, pre drivers? drivers? Actually, I love collecting, repairing, and using rare, basically worthless things!

 

[gadget73]

Whats it putting into the speakers? I can't exactly hear what you're describing but the speakers on this laptop are horrible. Thinking just feed in a sine wave and see what comes out the other end.