Meter test

[Suger]

I guess you're going to see me coming for every test... Should I open a new topic each time, or continue in a previous topic?

Anyhow, I failed. Again. I'm at the meter test stage. I have checked all solders, have no resistance where I should not have any, but when I turn the amp on, the meter first surges, then immediately goes back to 0.

Only two weird things I've found are with the 9.09ohms resistors (where I measure a resistance more around 1.15 ohms) and the 249kiloohms resistor, where I measure a resistance more in the 2K range. I've checked the stripes and am pretty sure I used the right resistors.

As usual, any help would be very much appreciated.

 

[Paul Birkeland]

Those are 2.49K resistors that you've installed, not the 249K parts.

What does the meter show with the amp turned on?

 

[Suger]

Oops.

For the meter, see the attached video in the first post. It climbs to about 1/3 of the range, then goes back down to 0.

Will change the resistors and see what happens...

 

[Paul Birkeland]

Once it has gone back down to 0, can you measure the DC voltage across the 910 ohm resistor?

 

[Suger]

I get 49.7V. Also, there is a definite improvement: the meter goes up, then down, then up again slowly. It stabilises in the low 20s, though, so I guess something is still wrong.

(That's after changing the resistor).

Also note that I get about 1.9 ohms resistance betweeen the two lugs of the meter, which I find weird. With the three 9.09 ohms resistance mounted in parallel, theoretical calculation show that I should have 3.03 ohms there (1/((1/9.09)*3). I've tested the three remaining resistances from the same set, they are 9.09 ohms, so I have a feeling something is off there.

 

[Paul Birkeland]

(That's after changing the resistor).

What resistor did you change?  Why did you change it?

The three 9.09 resistors are in parallel with the resistance of the meter.

I would not focus on the meter itself if the voltage across the 910 ohm resistor isn't stable. The meter is just telling you that you have a problem somewhere else.

 

[Suger]

I changed the 2.49k resistor for a 249k, as per your remark yesterday (manual, p. 51. I'd installed a red yellow white brown brown instead of a red yellow white orange brown).

Also, I just checked. When I turn the amp on, the voltage through the 910 ohm resistor is stable (at 59V). But I guess that's not the right value, right?

 

[Paul Birkeland]

A stable 59V would be the correct voltage across the 910 ohm resistor, and the meter reading should be stable under these conditions as well.

 

[Suger]

OK. Let's not concentrate on the why (I have no idea), or the how. But you're right. I now pass the meter test.

Once again, thanks for your patience. See you for the final voltage test/driver bias, I guess...

 

[Paul Birkeland]

OK. Let's not concentrate on the why (I have no idea), or the how.

Solder joints.

 

[Suger]

Always!