[rbarth]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif See if you can measure a resistance difference in RR3 when you turn it (amp off!) - measure the two pins underneath the PCB that are not connected, turn the screw about a half dozen times in either direction and measure the pins afterward each time. If that seems to work, give us some pics of the PS section. Used to, this issue could've been a result of turning the small cap around in the PS, but we've changed the parts since that time, so I'm a bit unsure what it might be if the trimmer checks out. 30.3VDC is just about what you should get if there's no regulation whatsoever, so it could be the LM317, too. As I said, give us some pics if the trimmer checks out OK.

With the amp off and measuring from underneath the two pins of RR3 that are not connected, my resistance readings are the same no matter how much I turn the screw in either direction. The meter always stabilizes at 00.4 ohms. So, am I right in saying that this trimmer doesn't check out and needs to be replaced?

 

[tomb]

Quote:

Originally Posted by rbarth /img/forum/go_quote.gif With the amp off and measuring from underneath the two pins of RR3 that are not connected, my resistance readings are the same no matter how much I turn the screw in either direction. The meter always stabilizes at 00.4 ohms. So, am I right in saying that this trimmer doesn't check out and needs to be replaced?

YES.

YGPM.

 

[rbarth]

I replaced the RR3 and am still having the same problem: the voltage reading doesn't change when spinning the trimmer screw. The old trimmer gave a reading of 30.3 VDC, the new trimmer is giving me a 29.5 VDC reading, no matter what. I am a newbie, however I'm certain that I'm using my multimeter properly, that it's working OK and that I installed the RR3 properly. Also, since I was given a caution about how sensitive this part is to heat, I was very careful about that when soldering the new RR3 in. Attached are two pics of my board, a full shot and one that focuses on the power supply. What do I do next? Thanks.

EDIT: Oh my goodness, the pics are terrible quality. Guess they were downsized because they are JPEG images. Sorry about that.

 

[tomb]

Quote:

Originally Posted by rbarth /img/forum/go_quote.gif I replaced the RR3 and am still having the same problem: the voltage reading doesn't change when spinning the trimmer screw. The old trimmer gave a reading of 30.3 VDC, the new trimmer is giving me a 29.5 VDC reading, no matter what. I am a newbie, however I'm certain that I'm using my multimeter properly, that it's working OK and that I installed the RR3 properly. Also, since I was given a caution about how sensitive this part is to heat, I was very careful about that when soldering the new RR3 in. Attached are two pics of my board, a full shot and one that focuses on the power supply. What do I do next? Thanks. EDIT: Oh my goodness, the pics are terrible quality. Guess they were downsized because they are JPEG images. Sorry about that.

Are you sure you've turned RR3 enough turns? 29.5 is almost exactly what you should get at maximum voltage. The LM317 will not allow any higher voltage, so it will seem as if turning the trimmer further in that direction will not work.

However, turn the trimmer in the other direction and you should see that voltage go down. Which direction? I don't remember off hand, but the Murata trimmers have clutches that prevent damage if you turn too far. This may seem like a hassle, but you should attempt turning the trimmer at least 20 turns in one direction. If no response, then turn at least 20 turns in the other direction. You should see that voltage start to drop about 0.1V per turn or thereabouts when you hit the range.

Let us know how that turns out. If unsuccessful, try again at the photos. We can't tell anything from those. See if you can use the macro setting on your camera and end up with a photo that just covers the heat sink area.

 

[tomb]

I just wanted to update anyone that was following rbarth's problems. We discovered offline that one of the PS diodes was reversed. Rbarth fixed that and is now enjoying a fully operating MiniMAX.

 

[Amarphael]

Hello all,

My newly aquired Minimax is giving me the same trouble as rbarth was having, But in my case the unresponsive trimmer is at the right tube bias, RA1R. I did the check that was suggested and resistance measures are the same regardless. I guess i should purchase a new trimmer? Can it be possible for this component to get faulty during transit or from repeated power on/offs?

 

[tomb]

Quote:

Originally Posted by Amarphael /img/forum/go_quote.gif Hello all, My newly aquired Minimax is giving me the same trouble as rbarth was having, But in my case the unresponsive trimmer is at the right tube bias, RA1R. I did the check that was suggested and resistance measures are the same regardless. I guess i should purchase a new trimmer? Can it be possible for this component to get faulty during transit or from repeated power on/offs?

No - it is not, but if it's a trimmer without a clutch, it's easily ruined by someone turning the screw too far past the audible clicks (signifying the end of travel).

Note that IMHO, rbarth did not have a bad trimmer despite what he apparently measured. Replacing his trimmer had no effect. Instead, there was a reversed diode in the mix all along. To measure the trimmer's resistance, you have to select the correct two terminals on the bottom of the PCB to measure on the trimmer. Further, you need to be sure you turn it in both directions. If it does have a clutch, turns in the same direction at the end of its travel will register no change. Turn the screw the other way, and it should start varying.

Many people think the tube trimmers have no effect, but they're just not turning them far enough. (Don't turn past a click, if you hear one, though.) You see, for the adjustment to work for 3 different tube types, each with differing gains, the trimmers need to have a very wide range of adjustment. This means that for a given tube type, it may only have a useful range of adjustment in the first or last 5 turns of the 25-turn trimmer.

 

[Amarphael]

My right bias is at 23.75V constantly, It didn't flinch one bit and I turned it a whole lot more than 25 turns in either direction, Until the the clicks showed up. Is this voltage rating maximal for the 12FM6?

Ichecked with the unconnected terminals as shown.
][/url]

 

[tomb]

Quote:

Originally Posted by Amarphael /img/forum/go_quote.gif My right bias is at 23.75V constantly, It didn't flinch one bit and I turned it a whole lot more than 25 turns in either direction, Until the the clicks showed up. Is this voltage rating maximal for the 12FM6? Ichecked with the unconnected terminals as shown. ][/url]

Well, we need to know more information. First of all, if you're just checking for whether the trimmer is OK, you need to measure resistance - not volts, and the amp needs to be turned OFF. If you attempt to measure voltage, it's not going to tell you anything - the voltage won't change unless the tube is in, is lit, and is operating correctly. Did you have the tube in when you were making these voltage measurements?

Let us know the complete picture of what you're doing:
Amp on or off?
Tube in or not, is it lit and warm?
What are you measuring and from what and where?

Again, turn the amp off and measure resistance only on those points in the pic you posted. Turn the trimmer about ten turns or so one direction and see if the resistance value changed. If not, then turn ten turns the other direction and see if the resistance value changed. That's the way you check to see if the trimmer is good - whether its resistance is changing when you turn the screw.

Too many other things have to be right (mainly the tube) if you attempt to measure bias voltage with the amp on and the tube in. According to your complaint, the first thing we want to do is eliminate this suspicion that the trimmer is messed up (I seriously doubt it).

 

[Amarphael]

I apologize that i got you confused. I measured resistance alright

The amp was off, tubes in. The reading was constant on 4.865ohms on the RA1R, on the RA1L it was 1.8 something and went down when i did a few turns counterclockwise.

I'm also fairly sure that it couldn't have been damaged in transit (it's a passive component) so i think the fella i bought it from messed it up like this and didn't tell me about it. I also wonder how the DB Bias reached more than 200mV when i got it...

 

[tomb]

Quote:

Originally Posted by Amarphael /img/forum/go_quote.gif I apologize that i got you confused. I measured resistance alright The amp was off, tubes in. The reading was constant on 4.865ohms on the RA1R, on the RA1L it was 1.8 something and went down when i did a few turns counterclockwise. I'm also fairly sure that it couldn't have been damaged in transit (it's a passive component) so i think the fella i bought it from messed it up like this and didn't tell me about it. I also wonder how the DB Bias reached more than 200mV when i got it...

OK - sounds like you did the right thing, then. I apologize for my confusion, too.

I guess the trimmer is bad after all. Usually they're bad to begin with, or are damaged when soldered in the board. I don't ever specify or supply the kind of trimmers that can be damaged by turning them too far. However, if it's one of those with a clicking warning - then they can be easily damaged if someone did that.

 

[dongringo]

Hi everyone,

Could you please check this out real quick and give me your opinion?

http://www.head-fi.org/forums/f6/did...inimax-482205/

My brother screwed up our first DIY project and I would like to know if we should just scrap it. Also, if we do solder another cap in, how do we test to make sure it works? We're new at this obviously.

Thanks for any info.

 

[tomb]

Quote:

Originally Posted by dongringo /img/forum/go_quote.gif Hi everyone, Could you please check this out real quick and give me your opinion? http://www.head-fi.org/forums/f6/did...inimax-482205/ My brother screwed up our first DIY project and I would like to know if we should just scrap it. Also, if we do solder another cap in, how do we test to make sure it works? We're new at this obviously. Thanks for any info.

I think the guys gave you some good answers in your other thread. Two things:
1. Take the drill away from your brother.

2. I wouldn't worry about doing anything more at this point. Just stick the leads of a new capacitor through the drilled holes and fill them with solder. Make certain that the solder touches both the leads and the solder pads on the back of the PCB. For the two pads close together, those are contacting the ground plane on top of the PCB. So, make sure you melt the solder well around the lead and both of those two pads - especially the inner one. The through-hole plating should be intact on the inner pad (it hasn't been drilled!!) and that should complete the electrical connection. The other drilled pad is connected to the trace on the bottom of the PCB and shouldn't be an issue when you fill that hole with solder on the bottom.

 

[dongringo]

Thanks Tom. Much appreciated. The drill has been confiscated.

 

[thebasso]

Hi everyone,

I was wondering if someone could tell me what kind of wire to use for the final wiring. Also, does someone happen to have a diagram of the wiring or a pic? Any info would be greatly appreciated. I can't possibly go through 65,000 posts to find the answer.

Thanks in advance.