Replace neons with LEDs in Fluke 845AB
Question for Dallas Smith:
I want to replace neons with LEDs in my Fluke 845AB.
Following your instructions below, did you mount the LEDs where the neons
were on the PCB and use the plastic light tubes or did you mount the LEDs
hard up against the LDRs in the yellow foam block?
Thanks, Lou
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Dallas Smith, 2 years ago
Permalink http://narkive.com/bdOZWNXt.1
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“Finally got around to modify my Fluke 845ab with LED 's for the chopper
circuit. Used the 17 volt windings for LED's (Mouser
941-C513AMSNCW0Y0511 Warm White Round LED) instead of the 130 volt, move
red wire on transformer pin 9 to pin 7.This winding is 180 degrees out
of phase, so I reversed the steering diodes (CR106 & CR107) I left in to
help make sure the phase was correct for the LED's when connecting.
Change R154 to 6K to set the brightness, selected for good operation of
the zero control. Then install jumper to replace C119. Also changed the
filter integration response caps C111 to .022uF and C116 to 47uF, this
stabilized the jitter to a manageable mode of operation. Meter now works
as well or better when the original neon's worked.”
Lamp Blocks
Hi Lou,
Its been awhile since I made this mod, but I had the foresight to save
the project to K04BB's site.
K04BB /Fluke/Fluke 845A AB
http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Fluke/Fluke_845A_AB
Still works great, hope you have the same results.
Dallas
On 6/5/2016 9:51 PM, Lou Amadio wrote:
Question for Dallas Smith:
I want to replace neons with LEDs in my Fluke 845AB.
Following your instructions below, did you mount the LEDs where the neons
were on the PCB and use the plastic light tubes or did you mount the LEDs
hard up against the LDRs in the yellow foam block?
Thanks, Lou
Quote
Dallas Smith, 2 years ago
Permalink http://narkive.com/bdOZWNXt.1
Raw Message
Report
“Finally got around to modify my Fluke 845ab with LED 's for the chopper
circuit. Used the 17 volt windings for LED's (Mouser
941-C513AMSNCW0Y0511 Warm White Round LED) instead of the 130 volt, move
red wire on transformer pin 9 to pin 7.This winding is 180 degrees out
of phase, so I reversed the steering diodes (CR106 & CR107) I left in to
help make sure the phase was correct for the LED's when connecting.
Change R154 to 6K to set the brightness, selected for good operation of
the zero control. Then install jumper to replace C119. Also changed the
filter integration response caps C111 to .022uF and C116 to 47uF, this
stabilized the jitter to a manageable mode of operation. Meter now works
as well or better when the original neon's worked.”
Lamp Blocks
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For Dallas Smith
Thanks for the info. It is in keeping with the original design.
My 845AB 15v supplies are currently down and I suspect the germanium
transistors around T202 may be leaky?.
Am thinking of replacing them with Si transistors. Your thoughts?
Regards, Lou
On Mon, Jun 6, 2016 at 12:35 PM, Dallas Smith dosmith@outlook.com wrote:
Hi Lou,
Its been awhile since I made this mod, but I had the foresight to save the
project to K04BB's site.
K04BB /Fluke/Fluke 845A AB <
http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Fluke/Fluke_845A_AB
Still works great, hope you have the same results.
Dallas
On 6/5/2016 9:51 PM, Lou Amadio wrote:
Question for Dallas Smith:
I want to replace neons with LEDs in my Fluke 845AB.
Following your instructions below, did you mount the LEDs where the neons
were on the PCB and use the plastic light tubes or did you mount the LEDs
hard up against the LDRs in the yellow foam block?
Thanks, Lou
Quote
Dallas Smith, 2 years ago
Permalink http://narkive.com/bdOZWNXt.1
Raw Message
Report
“Finally got around to modify my Fluke 845ab with LED 's for the chopper
circuit. Used the 17 volt windings for LED's (Mouser
941-C513AMSNCW0Y0511 Warm White Round LED) instead of the 130 volt, move
red wire on transformer pin 9 to pin 7.This winding is 180 degrees out
of phase, so I reversed the steering diodes (CR106 & CR107) I left in to
help make sure the phase was correct for the LED's when connecting.
Change R154 to 6K to set the brightness, selected for good operation of
the zero control. Then install jumper to replace C119. Also changed the
filter integration response caps C111 to .022uF and C116 to 47uF, this
stabilized the jitter to a manageable mode of operation. Meter now works
as well or better when the original neon's worked.”
Lamp Blocks
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Hi Lou,
It's normal for some leakage in germanium transistors. Do you have a
curve tracer?
If you change them to Si you will have to re-bias them (i.e. R207_8).
The 84 Hz may change also, might have to adjust C203.
But should be possible.
Dallas
On 6/6/2016 7:33 AM, Lou Amadio wrote:
For Dallas Smith
Thanks for the info. It is in keeping with the original design.
My 845AB 15v supplies are currently down and I suspect the germanium
transistors around T202 may be leaky?.
Am thinking of replacing them with Si transistors. Your thoughts?
Regards, Lou
On Mon, Jun 6, 2016 at 12:35 PM, Dallas Smith dosmith@outlook.com wrote:
Hi Lou,
Its been awhile since I made this mod, but I had the foresight to save the
project to K04BB's site.
K04BB /Fluke/Fluke 845A AB <
http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Fluke/Fluke_845A_AB
Still works great, hope you have the same results.
Dallas
Hi Dallas, no, I do not have a curve tracer but I have an oscilloscope and
function generator. What do you suggest?
The +/-15v is really low so I need to do something.
If I change to Si, are R207_8 likely to be lower or higher?
Regards
Lou
..............................................................................................................
On 7 Jun 2016 2:26 am, "Dallas Smith" dosmith@outlook.com wrote:
Hi Lou,
It's normal for some leakage in germanium transistors. Do you have a curve
tracer?
If you change them to Si you will have to re-bias them (i.e. R207_8).
The 84 Hz may change also, might have to adjust C203.
But should be possible.
Dallas
On 6/6/2016 7:33 AM, Lou Amadio wrote:
For Dallas Smith
Thanks for the info. It is in keeping with the original design.
My 845AB 15v supplies are currently down and I suspect the germanium
transistors around T202 may be leaky?.
Am thinking of replacing them with Si transistors. Your thoughts?
Regards, Lou
On Mon, Jun 6, 2016 at 12:35 PM, Dallas Smith dosmith@outlook.com
wrote:
Hi Lou,
Its been awhile since I made this mod, but I had the foresight to save
the
project to K04BB's site.
K04BB /Fluke/Fluke 845A AB <
http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Fluke/Fluke_845A_AB
Still works great, hope you have the same results.
Dallas
volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
Hi Lou,
What voltage are on the 15 volt rails? They are not regulated ±1 volt
seems reasonable. Check/Replace C117, C118, Q111, Q112; these are the
only components that can significantly draw the supplies down. If your
unit is like mine the carbon resistors have changed 30 % by now in the
positive direction. Also check for the regulated +10 volt supply at
CR105. What is the reading on your meter semi range of your digital ohm
meter across the emitter/collector? When using digital ohm meter to
check semi's, the reading is actually the voltage across the junctions.
What is the six junction readings you get on the EBC on the transistors?
(forward and reverse readings).
Dallas
On 6/7/2016 2:05 AM, Lou Amadio wrote:
Hi Dallas, no, I do not have a curve tracer but I have an oscilloscope and
function generator. What do you suggest?
The +/-15v is really low so I need to do something.
If I change to Si, are R207_8 likely to be lower or higher?
Regards
Lou
..............................................................................................................
On 7 Jun 2016 2:26 am, "Dallas Smith" dosmith@outlook.com wrote:
Hi Lou,
It's normal for some leakage in germanium transistors. Do you have a curve
tracer?
If you change them to Si you will have to re-bias them (i.e. R207_8).
The 84 Hz may change also, might have to adjust C203.
But should be possible.
Dallas
Silicon replacements should work fine; I would try the TIP30 or other
low current and slow power transistors like the BD234/BD236/BD238. The
only thing I would worry about is oscillation during switching if the
replacements are too fast and that is something I would check with an
oscilloscope by monitoring the collector waveform.
The transistors operate in saturation so the bias change will be
insignificant; the higher Vbe of silicon will lower the frequency by
about 3%.
I could not find any data on the GA2817 shown in the parts list. The
minimum Vce in the circuit is double the supply voltage. I think Ic
is below 100 milliamps.
On Mon, 6 Jun 2016 12:25:32 -0400, you wrote:
Hi Lou,
It's normal for some leakage in germanium transistors. Do you have a
curve tracer?
If you change them to Si you will have to re-bias them (i.e. R207_8).
The 84 Hz may change also, might have to adjust C203.
But should be possible.
Dallas
On 6/6/2016 7:33 AM, Lou Amadio wrote:
For Dallas Smith
Thanks for the info. It is in keeping with the original design.
My 845AB 15v supplies are currently down and I suspect the germanium
transistors around T202 may be leaky?.
Am thinking of replacing them with Si transistors. Your thoughts?
Regards, Lou
Hi David,
That's just what I was thinking. As well I couldn't find any data on the GA2817's.
Do you think the transistors are actually bad?
What is the status of the new modern chopper design talked about in earlier post?
Is there a PCB design now for it?
Dallas
From: davidwhess@gmail.com
To: volt-nuts@febo.com
Date: Tue, 7 Jun 2016 11:18:56 -0500
Subject: Re: [volt-nuts] Replace neons with LEDs in Fluke 845AB
Silicon replacements should work fine; I would try the TIP30 or other
low current and slow power transistors like the BD234/BD236/BD238. The
only thing I would worry about is oscillation during switching if the
replacements are too fast and that is something I would check with an
oscilloscope by monitoring the collector waveform.
The transistors operate in saturation so the bias change will be
insignificant; the higher Vbe of silicon will lower the frequency by
about 3%.
I could not find any data on the GA2817 shown in the parts list. The
minimum Vce in the circuit is double the supply voltage. I think Ic
is below 100 milliamps.
On Mon, 6 Jun 2016 12:25:32 -0400, you wrote:
Hi Lou,
It's normal for some leakage in germanium transistors. Do you have a
curve tracer?
If you change them to Si you will have to re-bias them (i.e. R207_8).
The 84 Hz may change also, might have to adjust C203.
But should be possible.
Dallas
On 6/6/2016 7:33 AM, Lou Amadio wrote:
For Dallas Smith
Thanks for the info. It is in keeping with the original design.
My 845AB 15v supplies are currently down and I suspect the germanium
transistors around T202 may be leaky?.
Am thinking of replacing them with Si transistors. Your thoughts?
Regards, Lou
volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
On Tue, 7 Jun 2016 13:06:47 -0400, you wrote:
Hi David,
That's just what I was thinking. As well I couldn't find any data on the GA2817's.
Do you think the transistors are actually bad?
It is not real clear from the description what is going on. Lou
wrote:
My 845AB 15v supplies are currently down and I suspect the germanium transistors around T202 may be leaky?
and
The +/-15v is really low so I need to do something.
Assuming that +/- 15 volts is in fact missing completely, I think one
or both Q201 and Q202 are the most likely fault.
It would take an awful lot of leakage to cause the inverter to fail
and if that happened, the transistors would self destruct anyway so if
they were leaky once, they are not anymore; they are shorted or open
instead.
There is no short circuit current limiting so the various rectifiers
should be checked also.
The transistors I mentioned are inexpensive and readily available.
What is the status of the new modern chopper design talked about in earlier post?
Is there a PCB design now for it?
Dallas
You would know more than I. I mostly lurk here. :)
The described replacement of the neon bulbs with LEDs looks easy and
reliable but I would try to fix the original circuit first. Either
way, the inverter has to be repaired.
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
On Wed, Jun 8, 2016 at 1:29 AM, Dallas Smith dosmith@outlook.com wrote:
Hi Lou,
What voltage are on the 15 volt rails? They are not regulated ±1 volt
seems reasonable. Check/Replace C117, C118, Q111, Q112; these are the only
components that can significantly draw the supplies down. If your unit is
like mine the carbon resistors have changed 30 % by now in the positive
direction. Also check for the regulated +10 volt supply at CR105. What is
the reading on your meter semi range of your digital ohm meter across the
emitter/collector? When using digital ohm meter to check semi's, the
reading is actually the voltage across the junctions. What is the six
junction readings you get on the EBC on the transistors? (forward and
reverse readings).
Dallas
On 6/7/2016 2:05 AM, Lou Amadio wrote:
Hi Dallas, no, I do not have a curve tracer but I have an oscilloscope and
function generator. What do you suggest?
The +/-15v is really low so I need to do something.
If I change to Si, are R207_8 likely to be lower or higher?
Regards
Lou
..............................................................................................................
On 7 Jun 2016 2:26 am, "Dallas Smith" dosmith@outlook.com wrote:
Hi Lou,
It's normal for some leakage in germanium transistors. Do you have a
curve
tracer?
If you change them to Si you will have to re-bias them (i.e. R207_8).
The 84 Hz may change also, might have to adjust C203.
But should be possible.
Dallas
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