Meter test

Suger · 10660

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Offline Suger

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on: February 08, 2022, 03:59:33 AM
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.



Offline Paul Birkeland

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Reply #1 on: February 08, 2022, 04:42:36 AM
Those are 2.49K resistors that you've installed, not the 249K parts.

What does the meter show with the amp turned on?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Suger

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Reply #2 on: February 08, 2022, 04:58:57 AM
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...



Offline Paul Birkeland

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Reply #3 on: February 08, 2022, 05:19:25 AM
Once it has gone back down to 0, can you measure the DC voltage across the 910 ohm resistor?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Suger

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Reply #4 on: February 09, 2022, 02:12:29 AM
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.
« Last Edit: February 09, 2022, 05:13:20 AM by Suger »



Offline Paul Birkeland

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Reply #5 on: February 09, 2022, 05:50:43 AM

(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.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Suger

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Reply #6 on: February 09, 2022, 06:03:44 AM
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?




Offline Paul Birkeland

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Reply #7 on: February 09, 2022, 06:09:10 AM
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.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Suger

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Reply #8 on: February 09, 2022, 06:13:19 AM
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...



Offline Paul Birkeland

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Reply #9 on: February 09, 2022, 06:14:32 AM
OK. Let's not concentrate on the why (I have no idea), or the how.
Solder joints.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Suger

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Reply #10 on: February 09, 2022, 06:45:54 AM
Always!