[volt-nuts] Replace neons with LEDs in Fluke 845AB

Dallas Smith dosmith at outlook.com
Wed Jun 8 13:19:25 EDT 2016


Hi Lou,

I think we should talk to each other. Send me your phone number to 
dosmith at outlook.com.

I'm confused to the state your meter is in, you already made the mod and 
now you are having problems? Or it's not working before the mod? When I 
made my mod it pulled the rails to ±14 volts. It was a compromise 
between brightness and performance. I tried many LED's and the ones I 
selected were just right. The right brightness to current draw and the 
correct wavelength for the photo cells. My instructions are not as clear 
as it should be for the T202 move wire from pin 9 to 7. The high voltage 
winding are abandoned and the led's are powered by the winding that 
supply the ±15 volts. I may have to look at my meter to see better what 
was done.

I work second shift, whats a good time to talk? I go to work at 3pm and 
return at midnight.

Dallas

On 6/8/2016 1:24 AM, Dallas Smith wrote:
> Hi Lou,
>
> I believe that the transistors are good. If they do not run to hot to 
> hold on to.
> Yes CR105 feeds the negative supply. Did you check CR104 and CR105?
> Q203 and Q204 should also be check since they could shunt the 
> transformer.
> Is transformer T202 and T203 hot. The high voltage windings on T202 
> could be leaky.
> Try taking out C119, did rails go to approximately 15 volts?
> Time to start isolating the supplies to various circuits to find the 
> culprit by removing one leg of various resistors.
> You can deal with the carbon resistor accuracies later.
> I had all many issues with my meter, after all their very old.
>
> Dallas
>
> On 6/7/2016 11:09 PM, Lou Amadio wrote:
>> Hi Dallas
>> I set my DMM on Diode Check mode:
>> Q201, PNP, no part number: EB/BE=0.23/Hi, CB/BC=0.21/Hi, EC/CE=Hi/Hi
>> Q202, PNP, no part number: EB/BE=0.22/Hi, CB/BC=0.20/Hi, EC/CE=Hi/Hi
>> Q111, NPN, 2N1304: EB/BE=Hi/0.28, CB/BC=Hi/0.26, EC/CE=Hi/Hi
>> Q112, PNP, 2N1305: EB/BE=0.26/Hi, CB/BC=0.25/Hi, EC/CE=Hi/Hi
>>
>> The two 15v rails are down to about 5v each. The oscillator is 
>> working but
>> fluctuating badly on frequency.
>> Replaced all the electro caps. Have not replaced the resistors or 
>> diodes.
>> Will check these next.
>>
>> CR105 feeds the neg 15v supply cap??
>> Regards
>> Lou
>>
>
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