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22 May 2023, 22:45
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#1 |
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Registered User
Join Date: Jul 2020
Location: Italy
Posts: 10
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Amiga 1200 board rev 1a green missing
The amiga 1200 missing the green color. I checked the voltages with pro tracker and U30 voltages in RED line, pin 26, are 0.23v MIN RED and 0,49v MAX RED.
The same check with GREEN line, pin 25, are 0,74v MIN GREEN and 1v MAX GREEN. I checked the resistors and the values are corrects. I checked the connections and the R231B point 2 is connected to pin 25 but missing the connection with the R232B point 1. (GREEN LINE) I followed the line of R232B point 1 and is connected to the C212 in the rear of board for the composite U12 encoder. Can I make a bridge between R232B point 1 and R231B point 2? (yellow line in the board picture board_miss.jpg) In the board I didn'd find any bad tracks, the components are near. P.S. The R232B point 2 is correct connected to the DB23S, video out connector CN9. |
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23 May 2023, 00:24
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#2 |
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Registered User
Join Date: Jun 2010
Location: PL?
Posts: 2,745
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Broken via? try to connect point to point with some enameled wire or so called kynar wire. Would be nice to inspect signals with oscilloscope...
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23 May 2023, 10:51
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#3 |
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Registered User
Join Date: Jul 2020
Location: Italy
Posts: 10
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I don't have a oscilloscope but only logic probe. I didn't understand why is broken tracks because are near components.
I'll try with wire connection |
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23 May 2023, 11:47
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#4 |
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Registered User
Join Date: Jun 2010
Location: PL?
Posts: 2,745
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Not necessarily it need to be broken track it can be broken via (joint between layers - small hole in PCB metalized to connect different layers - they can broken if PCB is for example bend or due of corrosion.
Seem cheap multimeters with embedded scope are available today (saw review on EEV Blog - ZT-702s) - perhaps consider to buy such thing as it may be very helpful for tracing such issues. Continuity tester may fail if there are other components connected to track (like coils that can pass DC but attenuate AC). |
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24 May 2023, 09:16
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#5 |
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Registered User
Join Date: Jul 2020
Location: Italy
Posts: 10
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I connected with a wire the resistors and now the green color is correct and the image is good.
Thanks |
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24 May 2023, 19:26
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#6 | |
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Registered User
Join Date: Jun 2010
Location: PL?
Posts: 2,745
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Quote:
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