Hi! Yeah, everything seems stable on the +-5v side. I will try to replace all the caps. But probably the screen is going bad :(
Thank you, > On Oct 14, 2018, at 10:57 AM, Fugu ME100 <b4me...@hotmail.com> wrote: > > Hi > > If the voltage change on pin 4 is smooth the voltages look right - pg 38 > of the M100 reference manual gives 0-4V as the range for V2. It feels > like VR1 is working correctly, indeed the whole contrast circuit would > appear to be fine. > > With the screen plugged in can you measure the -5V and +5V voltages at > their respective test points. They should remain stable as the contrast > is changed. Also check the reset line to the LCD, it is pin 7. > > It is quite tricky to test with the screen plugged in, the only way I have > been able to do that is to take the screen out to get at the connector > pins. > > Although it may appear good the -5V supply could still have problems due > to bad caps. Similarly the +5V could be bad too because of bad caps. It > sounds more like a power supply issue having to power cycle to make > things work properly. If one cap has been replaced I would probably just > replace all the power supply related caps. The 10uF caps always seem to > be dried up when I have had power supply issues. > > It could also just be a bad screen they do fail themselves due to age :( > > > On 14/10/18, 3:53 AM, "M100 on behalf of Rafael Arena" > <m100-boun...@lists.bitchin100.com on behalf of minikni...@hotmail.com> > wrote: > >> Hi! >> >> I tried what was suggested and I get 0-3.8v on pin four (without the >> screen plugged in). Can’t seem to figure out how to measure pin 4 with >> the screen plugged in. When i turn the contrast knob the screen starts >> to jump around the display random line sporadically. I have to turn the >> computer on and off a few times in order to get it to come on. >> >> Thank you, >> >>> On Oct 12, 2018, at 11:57 AM, Fugu ME100 <b4me...@hotmail.com> wrote: >>> >>> Hi >>> >>> The voltages look good. I usually replace C86 too it is part of the -5V >>> output circuit. >>> >>> You could try measuring the contrast voltage on the connector, pin 4, >>> see >>> if it smoothly transitions and there are no “jumps". Also check the -5V >>> is stable as you vary the contrast. I have noticed on some screens that >>> are failing the -5V will drop to -2V as the screen draws too much >>> current >>> as the contrast is varied. >>> >>> If the contrast voltage is not a smooth change then you could try >>> Brian’s >>> suggestion to clean VR1. >>> >>> Is it always missing a few lines on the screen? Do the missing lines >>> have >>> a pattern? >>> >>> On 12/10/18, 2:35 AM, "M100 on behalf of Rafael Arena" >>> <m100-boun...@lists.bitchin100.com on behalf of minikni...@hotmail.com> >>> wrote: >>> >>>> Hi, >>>> >>>> At times the computer comes on and when adjusting the screen display >>>> the >>>> image gets all distorted and then fades away. I have checked the +5 >>>> and >>>> -5 volts that the screen needs and I get +5 and -4.8 volts >>>> respectively. >>>> I changed capaciitor ‘C85’ and checked all the memory chips. Like I >>>> said >>>> it works every now and again, missing a few lines on the screen. When >>>> i >>>> play with the contrast knob the image distorts and some times fades >>>> away. >>>> Any of this makes sense? Lol >>>> >>>> Thank you, >>>> >>>>> On Oct 11, 2018, at 10:27 PM, Fugu ME100 <b4me...@hotmail.com> wrote: >>>>> >>>>> Hi >>>>> >>>>> What are the symptoms you are experiencing? >>>>> >>>>> VR1 could go bad but it could also be due to oxidation on the >>>>> resistors >>>>> tracks. People have tried to use contact cleaner to revive them. >>>>> Might >>>>> be worth looking into trying that option first? >>>>> >>>>> >>>>> On 11/10/18, 3:57 PM, "M100 on behalf of Rafael Arena" >>>>> <m100-boun...@lists.bitchin100.com on behalf of >>>>> minikni...@hotmail.com> >>>>> wrote: >>>>> >>>>>> Hello, >>>>>> >>>>>> I have a semi functional Model 100. I believe the issue is with the >>>>>> variable resistor ŒVR1¹. Where can I get a replacement? Do those >>>>>> VR¹s >>>>>> typically go bad? >>>>>> >>>>>> Thank you, >>>>> >>>>> >>> >>> > >
