68kMLA Classic Interface
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| Help identifying Apple Monitor H-card components | |
| Posted by: ktkm on 2019-08-03 07:05:41 I recently had one of my Apple Color High-Resolution Monitor Video Color Board ‘B-board’ re-capped. One of the large capacitors (22 µf 250 V ) had started to erode. The video was slightly improved, and the occasional shutting down issue seems to be gone. However, the H-board has a broken dial, and it is hopelessly awkward to adjust the horizontal centering ‘H.CENT’. So where can I buy this little dial (marked with magenta in the picture) and what is it called? Thanks! /ktkm  | |
| Posted by: cruff on 2019-08-03 09:32:43 Looks like a low profile potentiometer. If you can determine the value in ohms and the lead spacing, you should be able to select and buy a replacement from an electronic parts supplier. If you have the schematic and know the part identifier you should be able to figure what value is needed. | |
Posted by: ktkm on 2019-08-03 13:46:16 | |
Posted by: ktkm on 2019-08-03 13:53:33low profile potentiometerThank you! It is a ‘trim potentiometer.’ But how can I determine the resistance value? The ‘trimpot’ says: ‘102’ – is that a value? The size is approximate 7 mm. | |
| Posted by: cruff on 2019-08-03 18:01:07 That is likely to be a 1K ohm linear taper. 10 followed by 2 zeros. If the only issue is that the adjustment dial fell off, then you could remove the pot from the board and measure across the two legs that aren't connected to the wiper, which will be the pair on the flat side. That is an odd mounting method in the picture. | |
Posted by: ktkm on 2019-08-04 00:56:43That is likely to be a 1K ohm linear taper. 10 followed by 2 zeros. If the only issue is that the adjustment dial fell off, then you could remove the pot from the board and measure across the two legs that aren't connected to the wiper, which will be the pair on the flat side. That is an odd mounting method in the picture.I measured the pot in place, with the monitor turned off, to 1.078 kΩ, and with the monitor on, to 11.32 V DC. Later I found this one, could it be what I’m looking for in this case? When it comes to down to effect, the spec says 100mW, how do I measure that? | |
| Posted by: cruff on 2019-08-04 06:20:21 If there was 11.32 V across the pot, you divide by the resistance, 1 K, which gives you 11.32 mW, which is well within the specification for your new one. | |
| Posted by: ktkm on 2019-08-04 06:55:27 Great! Thank you so much @cruff for helping me out! I have learned a lot. | |
| Posted by: cruff on 2019-08-04 08:36:38 Wait, made a mistake, 11.32 V divided by 1 Kohm gives 11.32 mA. If you multiply 11.32 V by 11.32 mA you get 128 mW, which would exceed the rating of the pot by a bit. You might see if you can find a trim pot with a higher power rating. | |
| Posted by: ktkm on 2019-08-04 08:55:43 Thanks again! 🙂 | |
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