More infernal Beta Lead troubles

[archradish]

Well, the Power Amp problem I had got fixed a couple weeks back. But just last night at band practice it broke again in a different way.

We were rehearsing for a gig and playing quite loud. I started hearing a crackling coming through. At first I thought it was something in my pedal chain or something, then I realized that whenever the bassist in the band hit a really low note, or the drummer (who was right next to my amp) hit his kick, the crackling sound would come through my amp. The channel lights would flicker a bit as this happened (including the channel that I was not using). This gradually escalated to the point where the signal was becoming intermittent so i turned it off. I've read something on here before about their amp rattling itself to death and it seems like that's what happened here. Any ideas what the specific problem could be here? I'm dreading taking it to a tech again since last time took so long.

[EdBass]

That almost has to be a weak connection, a simple but possibly time consuming fix. I'd start with external cable connections and hope for the best, hopefully it's not internal but even if it is it's not generally a major issue.

[archradish]

Thanks for the feedback. I'm not qualified to make any kinds of repairs myself, but I'd like to know how much headache ($$$) I have to look forward to when I take it in. The last time I took it in it was there for 2 months.

[loudthud]

Problems of this nature are notoriously hard to cure because it is hard to re-create when the amp is taken apart for troubleshooting on the amp tech's bench. If the problem cannot be re-created, it's impossible to know if it's fixed or not. From my experience with Beta amps, I would guess that the -15V line has an intermittent connection between the power amp PCB and the preamp PCB. The important clue is the blinking of the Channel Select LEDs. The channel select logic and LED's on the preamp board run off of the -15V supply. The tech could try wiggling things to try to located something that causes the LEDs to blink, but it might not occur unless the amp gets really hot.

Possible causes are:

1) Bad solder connections on either the Power Amp or Preamp PCB's. This could be almost anywhere but most likely on Q11 on the Power Amp board. This transistor runs very hot and that could weaken the solder. That transistor could use a small heat sink but there is very little room on the PCB. It would be best to relocate Q11 (and Q1) off the PCB, attached to, but insulated from the chassis. Not a job your tech wants to do.

2) Probably the most likely cause is a bad connection at the Molex connector where wires plug on to Power Amp PCB. This type of connector is not very reliable. The solder connection to the PCB can become intermittent, the tin plating on the contacts can oxidize and the crimp connection to the wire can become intermittent. The contact with the wire attached should be removed from the housing, the crimp connection should be solderd and the terminal retentoned. Then the contacts should be sprayed with a contact solution to improve conductivity like Caig Deoxit.

Do not attempt these repairs yourself. Print this out and take it to your tech. If the problem cannot be recreated in a short length of time on the tech's bench, have the tech perform #2 above and give the amp back to you (you should pay him for his time) to test at rehearsal. If the amp still exhibits the problem when it gets hot, it needs to go back to the tech for more testing.

[archradish]

Thanks for the info. I will pass it on to the tech. I am in the process of building a new head shell for it to provide better ventilation (there air vents on the bottom are blocked off in the combo that it came in) so hopefully once it gets fixed it will stay that way for a while.