pucho812
Well-known member
anyone ever see volts increase by 10v when hooking up sub assemblies in a unit?
Here is a head scratcher
- Thread starter pucho812
- Start date
Help Support GroupDIY Audio Forum:
radardoug
Well-known member
Not much information, so hard to say.
pucho812
Well-known member
I know. Sorry.
So check it out. I have 2 x active crossovers on the bench. One is working as it should after replacing a couple of opamps.
The other is in a protection mode and it won’t leave protection mode.
Both units contain an I/o board on a sub assembly. Both I/o boards work with in the one working unit.
In the other unit when I connect either I/o board it goes into protection mode.
I have compared units and both main boards behave the same without the daughter board and show same voltages and same test points.
On the faulty unit I have traced a vdc line that comes off one of the power transformer secondaries. The power transformer has a center tap.
I get 38vac which is correct when measuring the from center tap to one of the windings. It feeds an IN4004 which then feeds a 5v Zener diode.
From there it goes off into the circuit and I am slowly tracing things out. At the zener output I get 27vdc. But the moment I connect the I/o board the same path measures 37vdc.
Last edited:
pucho812
Well-known member
More of the head scratcher. On the faulty motherboard.
a BC546 in circuit where I am discovering my issue
measures 10V at the collector, 2.2 volts at the base and 1.5 volts at the emitter but the moment I connect any working daughter board the 10V jumps to 37V. something is not working properly, yet all the individual components within that section all measure as they should out of circuit.
I can't see any leakage of the transistor and I can't measure any continuity to any other traces or components near by.
Sorry thinking out loud here but it seems bizarre that the entire line jumps about 10V with the daughter board and magically shows as 37V at the same collector that showed 10V without the daughter board connected. Clearly I am chasing something obvious I just can't see it.
a BC546 in circuit where I am discovering my issue
measures 10V at the collector, 2.2 volts at the base and 1.5 volts at the emitter but the moment I connect any working daughter board the 10V jumps to 37V. something is not working properly, yet all the individual components within that section all measure as they should out of circuit.
I can't see any leakage of the transistor and I can't measure any continuity to any other traces or components near by.
Sorry thinking out loud here but it seems bizarre that the entire line jumps about 10V with the daughter board and magically shows as 37V at the same collector that showed 10V without the daughter board connected. Clearly I am chasing something obvious I just can't see it.
Last edited:
scott2000
Well-known member
Could the zener be falling apart when taxed?
pucho812
Well-known member
head scratcher has been isolated to a custom discrete opamp. Luckily the opamp is exposed and thru-hole parts so should be easy to work out what failed and replace.
Pulling the doa out and the unit no longer stuck in protect mode.
Now to work out the doa.
Pulling the doa out and the unit no longer stuck in protect mode.
Now to work out the doa.
Last edited:
pucho812
Well-known member
It’s a custom piece that is entirely discrete components with active circuitry.
The main transistors in play are bc546 and 556, bd139 and 140.
There are some common Avalon discrete 2010 opamps in play and an Avalon 2012 which is another Avalon discrete opamp.
I have never seen a 2012 used anywhere else. The 2010 is found in the Avalon 2000 stuff, the 2044,2055,2077 and so on.
The moment I pulled the 2012’s everything was behaving as it should. Some went on those and had them pushing out dc.
Now I gotta source why and fix
MidnightArrakis
Well-known member
>> Any schematics available for this unit of yours.....even if it is "custom"?It’s a custom piece that is entirely discrete components with active circuitry.
The main transistors in play are bc546 and 556, bd139 and 140.
There are some common Avalon discrete 2010 opamps in play and an Avalon 2012 which is another Avalon discrete opamp.
I have never seen a 2012 used anywhere else. The 2010 is found in the Avalon 2000 stuff, the 2044,2055,2077 and so on.
The moment I pulled the 2012’s everything was behaving as it should. Some went on those and had them pushing out dc.
Now I gotta source why and fix
/
pucho812
Well-known member
This isn’t my unit. And there are no schematics
Voyager10
Well-known member
Can you post pictures of the insides?
pucho812
Well-known member
Need to wait on that but I can do that soon
pucho812
Well-known member
Update.
The custom opamps work but after some time start. To output dc. So I can measure dc in reference to ground and get nearly 0vdc at the output of the opamp, line 0.xx then out of nowhere I get full bore -28vdc. At the same point.
this is not good. Not sure how that is happening.
The custom opamps work but after some time start. To output dc. So I can measure dc in reference to ground and get nearly 0vdc at the output of the opamp, line 0.xx then out of nowhere I get full bore -28vdc. At the same point.
this is not good. Not sure how that is happening.
