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scar
Joined: 02 Jul 2015
Posts: 34
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 Posted: Sat Jul 04, 2015 5:40 pm Post subject: |
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| should i measure those with the board (43) still floating, or should i solder that back on at this point? |
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jts1957
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scar
Joined: 02 Jul 2015
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| Posted: Thu Jul 09, 2015 1:16 am Post subject: |
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ok on step #3 it says to test the AC inputs. the first measurements reads 1370 and after swapping the leads the read-out is 1367
in step #4, with the positive lead on an AC input and the negative lead on the positive output, the reading is 550 and then 547 with the other AC input. readings are about the same for the negative output |
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jts1957
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| Posted: Thu Jul 09, 2015 3:33 am Post subject: |
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Here's what I was taught:
'a' and 'b' can be done with the Bridge diode IN or OUT of the circuit, IF it tests good in circuit, it IS good. If it tests strangely in circuit, it's best to remove and retest out of circuit.
a) Put the black meter test lead on the Bridge 'Positive' leg - touch the meter's red test lead to one 'AC' leg and then to the other 'AC' leg. Then the reverse: Put the red meter test lead on the Bridge 'Positive' leg - touch the meter's black test lead to one 'AC' leg and then to the other 'AC' leg.
b) Put the red meter test lead on the Bridge 'Negative' leg - touch the meter's black test lead to one 'AC' leg and then to the other 'AC' leg. Then the reverse: Put the black meter test lead on the Bridge 'Negative' leg - touch the meter's red test lead to one 'AC' leg and then to the other 'AC' leg.
You should get two over-range readings with the leads connected one way and two numeric readings with the leads connected the other way for BOTH 'a' & 'b'.
Measuring between one 'AC' leg and the other 'AC' leg while the Bridge is still IN CIRCUIT and connected to a transformer's secondary will result in you reading the transformer winding. OUT OF CIRCUIT it should measure over-range.
Measuring between the 'Positive' leg and 'Negative' leg while the Bridge is still IN CIRCUIT depends on what else is in the circuit. OUT OF CIRCUIT it should measure over-range.
Assuming your meter is on the correct settings ('diode test" in particular) and is working correctly, remove bridge diode and retest it.
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scar
Joined: 02 Jul 2015
Posts: 34
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| Posted: Thu Jul 09, 2015 9:36 pm Post subject: |
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ok i removed it and re-tested it out of circuit...
| jts1957 wrote: |
You should get two over-range readings with the leads connected one way and two numeric readings with the leads connected the other way for BOTH 'a' & 'b'. |
this was the case |
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scar
Joined: 02 Jul 2015
Posts: 34
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| Posted: Thu Jul 09, 2015 9:44 pm Post subject: |
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BTW here is what the bottom of the circuit board looks like
seems there is a lot of residue or burn marks or something that doesn't look right.... |
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jts1957
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| Posted: Thu Jul 09, 2015 10:45 pm Post subject: |
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Remember to carefully resolder ANY suspicious joint(s) while you have access.
So was bridge good or bad?
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jts1957
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| Posted: Fri Jul 10, 2015 1:27 am Post subject: |
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| jts1957 wrote: |
You can check (Q1 thru Q4) between each output transistor leg and ground for shorts. Meter on Low to mid range, meter on OHMS.
You could put your meter on 'Diode Test' and check the bridge rectifier, if its NOT mounted flush to the board. |
You didn't try above and this? Meter on 'Diode Test.' Go between legs of EACH transistor TWICE, First with the Red meter lead to leg mentioned in the left column - Black meter lead to leg mentioned in the right column and Second with the Black meter lead to leg mentioned in the left column - Red meter lead to leg mentioned in the right column.
left and center
right and center
left and right
For EACH transistor that's six measurements. Ideally there should, on a standard transistor OUT OF CIRCUIT, be two 'LO' and four 'HIGH' readings. By 'LO' with a DVM on 'Diode Test' I mean a numeric reading usually above '500' ... By 'HIGH' I mean 'over-range.' IN CIRCUIT readings can be affected by whatever else is in the circuit.
In your instance you can fairly easily effectively take each transistor out of circuit by desoldering the left and right legs of each from the top of the board. Careful molten solder doesn't roam where you don't want it.
IF ANY of these tests result in a very low reading be sure to record which transistor/test and bring to my attention.
Residue / burn marks or something look normal for its age to me.
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scar
Joined: 02 Jul 2015
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| Posted: Fri Jul 10, 2015 4:50 am Post subject: |
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| jts1957 wrote: |
| So was bridge good or bad? |
it seems good, see my post here
ill try to test Q1 to Q4 tomorrow |
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scar
Joined: 02 Jul 2015
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| Posted: Thu Aug 06, 2015 10:16 pm Post subject: |
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| jts1957 wrote: |
Meter on 'Diode Test.' Go between legs of EACH transistor TWICE, First with the Red meter lead to leg mentioned in the left column - Black meter lead to leg mentioned in the right column and Second with the Black meter lead to leg mentioned in the left column - Red meter lead to leg mentioned in the right column.
left and center
right and center
left and right |
alright so i finally got some time to do this. i desoldered the left and right legs of each transistor (marked B and E on the diagram) and then tested according to your directions.
B = left leg
C = center leg
E = right leg
Q1:
Black lead on B:
Red on C = 002
Red on E = 002
Black lead on C:
Red on B = 002
Red on E = 002
Black lead on E:
Red on B = 002
Red on C = 002
Q2:
Black lead on B:
Red on C = high
Red on E = high
Black lead on C:
Red on B = 523
Red on E = high
Black lead on E:
Red on B = 540
Red on C = high
Q3:
Black lead on B:
Red on C = 002
Red on E = 002
Black lead on C:
Red on B = 002
Red on E = 002
Black lead on E:
Red on B = 002
Red on C = 002
Q4:
Black lead on B:
Red on C = 460
Red on E = 492
Black lead on C:
Red on B = high
Red on E = high
Black lead on E:
Red on B = high
Red on C = high
looks like Q1 and Q3 have strange results |
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