Fluke 5215A repair

[classicTEK]

Hello All,

I have come across a Fluke 5215A precision amplifier. It is FIXED at 100x amplification by design.

I have been trying to repair the preamplifier board and having trouble with this one.  I am specifically trying to follow the TS procedures in the manual on page 4-24.  When I get to step 10 I am to check the -31Vdc at TP17 and the +30.5Vdc at TP8.  I am measuring -33.04 and +32.2 at TP17 & TP8 respectively.  Since these measurements are out of tolerance, I am directed to go to step 12.

Step 12 directs me to check 40Vrms input to the bridge rectifier(CR182) and this is where I am stuck.  I am measuring 48.6Vrms across pins 5 & 7 of P20.  The input comes DIRECTLY from the AUX T3 to CR182.

What am I doing wrong or what could be causing me to measure high at the input to CR182?  The input to CR175, which is the rectifier for the 21Vrms, reads 21'ish Vrms.

Also, what is the best way to communicate the schematics?  The manual is the same all over the net so I thought folks would just download that and correlate the info I am referring to.

Which is best?

Cheers

[Daniel_Reyes]

How far out of tolerance is it? What do they give you for their upper and lower limits?

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[classicTEK]

HA!

The one piece I left out.  The spec is -31.0 +-1 Vdc at TP17 and +30.5 Vdc +-1Vdc at TP8.  I know it is nit picky, but just trying to follow the order of things.  I do however have the ability to think outside the box on occasion.  :  ))

It just that the 21 Vrms is so close to spot on that it makes me wonder.

d

[Daniel_Reyes]

Can you upload a picture of the circuit?

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[Daniel_Reyes]

It did, check the diodes. Maybe one is shorted. Ive seen that one power supplies before, after that, possibly transistor shorted,  after that, id have to look at the circuit again.

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[classicTEK]

The schematic......

[PA0PBZ]

This schematic is ... confusing. They mention minus 1.9KV for the anode of the 4X tube twice (right and top), but then on the left it is suddenly 1900V.
Then we have 2 caps C182 and C183 from CR182 +/- 29V to this HV line, the caps only being 40V
I wonder in reference to what you should measure the output voltage of CR182.

[classicTEK]

The manual TS procedures tell me to look for +31.0 & -30.5 on the output at TP8 and TP17.  The schematic says it should be +&-29.  The theory of operation also calls this out as +&-29.

The TS procedures tell me to put my DVM LO at TP7 and measure the output at TP8 & TP17.

It is confusing.  Is there anything I can do to help clarify?

Here is a link to the manual:  http://assets.fluke.com/manuals/5215A___imeng0000.pdf


Cheers,

David

[classicTEK]

Seriously.............no takers on this one folks?

bump

[Daniel_Reyes]

Did you check the diodes?

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[Squarewave]

I know this is an old thread, but I wondered if this was ever sorted.

I have one of these myself, it was given to me, but we're not really sure whether it works or not. I've not tried it yet because it's so heavy I can't move it to where I need it, yet.