Bugera Trirec Guitar Amp.... - Page 1
Forum section: electronics / repair

author: whipman
author_rank: Contributor
timestamp: January 07, 2015, 02:51:18 pm
content: Greetings All,I'm in the process of repairing a Bugera Trirec amp and I've narrowed it down to the 5V DPDT relays on the front control panel. My question is this. Of the 10 relays (when activated) 1 shows 5V at the coil the other 9 show 21-23 volts. Is 21-23 volts normal for a 5V relay? Am I doing something wrong?Thanks in advance!

author: Anks
author_rank: Frequent Contributor
timestamp: January 07, 2015, 04:55:37 pm
content: I'm confused as to what your actually measuring and what point of reference for the voltages your using. try measuring the voltages across the relays. Also are you sure the relays are 5 volt.What exactly is your issue with the trirec. I maybe able to help.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 07, 2015, 05:02:29 pm
content: If you mean that you are measuring 21-23V across the coil when energized, then NO that is not "normal".Assuming nominal conditions here. You aren't seeing some artifact of pulsed/switched drive current, etc.And assuming you mean "steady-state" and not some kind of transient when powered or released, etc. etc.However, It is hard to imagine how this symptom (however atypical) could have caused any change in how the unit is performing??You question only raises a dozen more questions.

author: whipman
author_rank: Contributor
timestamp: January 07, 2015, 05:37:09 pm
content: OK. A little more detail. I'm measuring + & - across the coil legs. The amp has various gain stages controlled by these relays and yes they are all standard 5V DPDT micro relays. It's a 3 channel amp that sounds fine clean. Once you begin switching channels for the various gain stages it goes from hissy to toneless and muffled. I've repaired tons of amps and have eliminated the usual preamp / power amp suspects. It's definitely in these relays / relay circuit somewhere. The channel selection is fine the gain stages are a mess. Thanks Guys!

author: krivx
author_rank: Frequent Contributor
timestamp: January 07, 2015, 06:13:48 pm
content: How are the relays driven? Have you tested those circuits? A large voltage across a relay would suggest that a protection diode may be dead, and that the relay drive may also be toasted.

author: Seekonk
author_rank: Super Contributor
timestamp: January 07, 2015, 06:30:52 pm
content: It sounds rather odd that one relay would have 5V and others have a much higher voltage. All relays should be powered from the same voltage source.

author: krivx
author_rank: Frequent Contributor
timestamp: January 07, 2015, 06:32:55 pm
content: If there is no diode across the relay a larger voltage may build up. Driving the relay is switching an inductive load.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 07, 2015, 06:38:41 pm
content: You did NOT mention whether the relays were actually SWITCHING when the voltage was applied to the coil?I can't imagine how nominal 5V relay coils would last very long with 4-5x volgage across them?Have you measured the resistance of those coils? Are the relay coils already burned out?Do you have a schematic diagram that shows the power source and switching circuit for these relays?It is almost shooting in the dark trying to offer any advice with virtually no context here.

author: whipman
author_rank: Contributor
timestamp: January 07, 2015, 06:49:02 pm
content: Not yet on the resistance. I shut it down when I saw those numbers. It's a little difficult as the board is still in the amp. I'm going to pull the board (major pita) then post back. Right now I'm working with a small mirror and led light to get a look at things.Thanks!

author: kezat
author_rank: Contributor
timestamp: January 07, 2015, 10:48:17 pm
content: With the limited access and the use of a mirror it could be easy to mix pins up, are you sure your measuring the Coil and not the output or a combination their of?

author: whipman
author_rank: Contributor
timestamp: January 08, 2015, 02:14:25 am
content: Turns out I had the right amp but wrong notes! I'm working on 3 different amps and wrote down the issues for each one & grabbed the wrong sheet of paper. Anyway, the one I originally posted about has 24V relays. Hence the "high" voltage readings. Ater I took it apart I realized my mistake. Sorry guys. As for the mirror I wasn't using it for the pins I was using it to try to read the numbers on the relays which are located on a pcb behind the front panel of the amp. I had clear access to the pins all along.