TRS80 Model 4P CRT contrast fail
binarydinosaurs at gmail.com
Sat Nov 25 10:05:39 CST 2017
> On 24 Nov 2017, at 08:44, Adrian Graham via cctalk <cctalk at classiccmp.org> wrote:
>> On 24 Nov 2017, at 08:41, Brent Hilpert via cctalk <cctalk at classiccmp.org> wrote:
>> On 2017-Nov-23, at 5:07 PM, Adrian Graham via cctalk wrote:
>>>> On 23 Nov 2017, at 21:18, Brent Hilpert via cctalk <cctalk at classiccmp.org> wrote:
>>>> You might check the contrast control.
>>>> I can't find the actual schematic for the contrast control connections, but I 'm guessing the ends are connected across 12V (video board pins 5 & 1/4/10) and the wiper to video board pin 8.
>>>> The contrast control can be expected to take pin 8 somewhere + to get pixels fully on.
>>> You’re right with pin 8, tracing the circuit I can see why someone recommended I check Q101 and Q102 which look OK in my tester.
>>> The contrast control itself tests OK resistance wise, it goes from pretty much 0ohms to 610M.
>> 610M ?
>> I hope that M is a typo.
> It is, 610k or 0.6M :)
Gah, ignore this.
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