Fluke 332D repair..still sorting issues

[wictor]

Valley, have you verified that those K1 and K2 relay are good and operating when safety switch is closed?

Wictor

[kawal]

I confused the versions of the Prereg. Mine has that weird resistor and your will not. In your case its R2 on top of the board (power sense resistor).  I would also check R6 which is part of the same circuit.
All this circuit is is a variable resistor (Q1) that reduces the voltage going to the  HV transformer. This makes the voltage only as high as it needs to be versus always 1200V.
With it out there is no dangerous voltages and should draw very little current and produce no heat.
There are at least 2 ways to check the preregulator. 
1) Take out the card and supply it +12/-12V - thi sis better as you will get the current draw - should be pretty small less than 50ma 
2) Solder wires to the card and measure externally but have car in the unit. - cant get current draw.

[valley001]

Forgive my ignorance but I am not certain exactly where I should apply 12v (is it terminations "a" and "p?")  and then where I should be measuring (where on the schematic). The board layout on my pre regulator is different from the picture in the manual.  I have been working up the courage to operate this thing with the panel removed but im not there yet..so a way to test out of the chassis would be welcome.

wictor- I did verify visually (peering through the holes in the outer case) that K1 is actuating.  Whether it is making good contact or not, I am not sure.    I am also not sure if K2 is operating.  It is open without power, I would apply 35v to it and it should close no? 

I do not have a proper low voltage power supply, so that leaves me using batteries to test.

[kawal]

Power supply makes it so easy to troubleshoot. Think about getting one. Maybe you have a transformer with 2x10V winding that will also work.
The place to connect would be at the capacitor after the bridge rectifier. Or directly at the rectifier.  If its better with dedicated S but yo could do it with some 12 V power bricks we all have laying around.


In case you have the same as me here is that version. The schematic is on 3330B manual .
The power resistor is the big flat thing also on top of the board (R2). Mine had bad solder joints from thermal cycling. This board gets toasty so might be good to resolder the bigger power devices. Clean up the flux after soldering.

The picture is before the repairs i did. Notice the burnt cables. These are signs of over current and something being wrong. In my case one of the transistors was low on HFe and R2 had a bad connection.

[kawal]

here is the repaired pre reg with comments

[valley001]

I think K2 may be faulty, is it safe to jumper it and then test the unit? 

I did operate it with the interlock engaged and confirmed that K1 closes when I switch to operate.  I dont know if this matters but I would expect to see a small spark from the contacts when the relay closes, I do not see a spark. 

[kawal]

Did you test it?  I think the K2 coil needs about 20V to turn on - apply 20V to the coil and check with ohm meter. Do not jumper the contacts . Its part of the safety feature of the unit.
K2 just controls the turining on of K1. So there must be a fault in the current limit board if K2 is not turing on.  I would not jumper anything in this beast. 

[valley001]

Understood..will not jumper. 

I tested K2 and it is functional and reads closed with +18 volts applied (2x 9v batts).

[kawal]

could be not enough voltage or contacts are welded.

[valley001]

I do have a 12v AC output wall wart, I suppose I could test the board with that?

[wictor]

I don't recommend that 12V AC for testing.

[valley001]

The voltages at pin 7,8 and 9,10..will those give me an idea of the problem is in the pre regulator board?

[wictor]

The voltages at pin 7,8 and 9,10..will those give me an idea of the problem is in the pre regulator board?

You should have some AC voltage between 7 & 6 on preregulator. And when safety switches are closed, you should have voltage between 9 & 6.

[valley001]

Between 7 and 6 I get 106v AC in standby and operate.
Between 9 and 6 I get .226v AC only in operate mode. 

I also checked the wave form of Q1 on my scope (scope not grounded per instructions), it does not change between standby and operate.  The standby wave form is about .5v pp, but does look to be the correct pattern.  Ill see if I can load a screenshot of it. 

[wictor]

Then there is something wrong in preregulator. Check the voltage path between 7 and 9.

[valley001]

WTF the unit is working now.  Outputting voltage to the terminals. 

[wictor]

Great[emoji16]

[wictor]

There are many possibilities for contact problems in those units.

[wictor]

And of course preregulator voltage between pins 9 &6 is depending of wanted output voltage.

[valley001]

The only difference between today and other days messing with this thing is that I have cycled many more times.  It takes a few times of switching to operate before it comes to life. 

I notice on the meter, it will flicker a bit before rising to voltage.  In the past I had a problem with electrolytic caps causing problems like this.  I guess I may recap the power supplies and clean all of the contacts I can reach. 

[Fred_47]

Rear Bulkhead Resistor

Yellow lead 748v

Series Pass

Collector Q8 137.5v

What is the part number of the bulkhead resistor on the schematic?

Have you noticed that there are 2 K1 relays? There is one in the preregulator ckts shown at the lower left on sh 1 of 332B-1001 and 1 in the interlock ckt shown on the right hand side of sh 2 of 332B-1001.

If the preregulator K1 doesn't pick up, there will be no high voltage from T2. There is still high voltage from T1 thru the bridge on the lower right on sh 1 of 332B-1001. This may be the source of the voltages you're measuring. Its purpose is to provide a minimum forward current thru the series pass ckt.

If interlock K1 doesn't pick up the negative leg from the HV ckts is disconnected from the output and you will read 0 or very low voltage at the output.

There are also 2 K2 relays. One is the 'crowbar' which throws a load across the HV capacitors to quickly lower the voltage. It is located a little below and right of center on dwg 332B-1001 sh 1. There is a  N.C. K1 contact in parallel with the K2 crowbar contact. (I don't know which K1 relay but I suspect it's the interlock K1)

The interlock K2 is shown in 2 places. One is at the lower left of sh 1 dwg 332B-1001 (to energize the preregulator K1) and also in the interlock on the right side of 332B-1001 sh 2. This one allows energizing the HV supply if all the cards & covers are in place.

I haven't figured out how the interlock K1 & K2 get energized. The circuit description says that they are energized by Q3 on the series pass driver board when relay K2001 is energized in STDBY. The drawings that I have show the connections but interlock K1 has diodes connected in opposition and the 332 dwg (sh 2 of 332B-1001) has a single diode connected in reverse of what I would expect. A drawing error to check out the next time I open the beast.

My 335D 'buzzes' when it is in current limit. The protection circuit trips on high voltage (as it should) and limits current on a short circuit (as it should).

Do you get any current reading on the meter?

Here are the 332 drawings I'm working from. They are from the April 1972  Rev 1 3/75 332D manual. (P/N353292) Do they match your unit?

I have 2 sets (1971 & 1978) for the 335 and a 4th set made up of a mix from 332/335 drawings that seem to match my 335D.

Also attached is a block diagram from the 335A/D 1/69 manual rev 1 8/71. The 332 is the same but without the null detector. The 335 HV assemblies are A8... and the 332 HV assemblies are A7.... The block diagram doesn't show the 500V supply feed from T1.

According to a note above the editor, there have been 8 new messages added to the tread since I started composing this. I see that today the 332 has decided to work.

[valley001]

Hi Fred,

Thanks for chiming in.  The K1 and K2 I was referring to are both on the Pre Regulator board. 

I still have the bad Q2 on the current limiter to change, maybe that is the cause of my buzzing. 

[Fred_47]

Hi Fred,

Thanks for chiming in.  The K1 and K2 I was referring to are both on the Pre Regulator board. 

I still have the bad Q2 on the current limiter to change, maybe that is the cause of my buzzing.

I don't think your Q2 is bad.

On Dwg 332B-1004, Q2 is a PNP that regulates the -35V supply. You reported upthread that the -35V supply is outputing -35V. The BOM lists a 2n2869 PNP Ge and the card in my 335D has a 2n5883 PNP Si with a 1991 date code. (Maybe the newest part that I didn't put in.)

Double check because there are a few different versions but all seem to have the same ±35V supply on the current limiter board.

Also, I found yet another relay labeled K1.

There is a relay 'K1' that is switched directly by the OFF-STDBY-ON switch that has contacts K1A and K1B. The relay is energized thru a time delay ckt between pin 8 & 12 on the Auxiliary Power Supply when the switch is turned to ON. The ckt is 40V from pin 15 to K1 to the ON switch to Pin 8. It has a contact K1A that parallels the crowbar in the HV supply and a contact K1B that shorts the output terminals thru a 5.1ohm resistor at the far right side of Dwg 332B-1001 sh 3.

I notice that the power distribution dwg in the 3/75 rev of the 332A/D manual doesn't show the capacitor that creates the time delay. It is shown on the Dwg 335A-1004 in the 1978 rev of the 335A/D manual which I attached in my 1st post to this thread. It's in the BOM for the 332 Aux Power Supply board (C1 68uF, 15V Ta on the Aux Power Supply, A5A5) .

The relay K1 that is in the interlock string has a contact that disconnects the neg output between the HV supply and output terminal.

The 3rd K1 is on the preregulator board and is energized by the K2 interlock relay using the AC power input. It drops out immediately if AC power is lost while the other relays hang on as the DC power decays.

I suspect that the reason for the convoluted circuitry is to make sure that the HV supply can't be connected unless the control voltages are energized and that the HV gets disconnected first in the event of any failure. Any one of the K1s failing to energize would have given symptoms similar to what you had. All of them are energized via various contacts which could have been dirty or oxidized or ....

There is a 4th K1 on the capacitor switch that controls the voltage on C5 when the range is down switched too fast. It apparently doesn't have any function beyond that.

[kawal]

The K1 you mention  on the preregulator board was the same K1 that I had to clean via taking the relay apart. There was heavy oxidation  on my unit and the cleaning removed all the oxidation. I reconnect you do that as you probably also have a lot of oxidation and carbon buildup on that K1.
I circled the contacts to clean but best way is to take the contacts out. Remove the spring on the back  and then you can remove the contact points for a good cleaning. This contractor has not protections from dust or other elements.

I found this in an application note from TE connectivity
"
Contact Materials
Fine Silver
Fine silver has the highest electrical and thermal properties of all metals.
It is the best general purpose material available. However, it is affected
by sulfidation. The rate of sulfidation indoors in a metropolitan area is
approximately 70 micrograms per square centimeter per day. This
sulfidation forms a film on the surface of the silver which increases contact
interface resistance.
Because silver and silver alloys sulfidate, contact pressures must be great
enough to break through this film. (Controlled arcing will also be helpful
in that it burns off the sulfidation, and contact overtravel wipes away the
residue.) While such pressures have no appreciable effect on silvercadmium contacts, they do result in increased material wear of fine silver
contacts. Also, an interface voltage of several tenths of a volt can result
with fine silver contacts because of the sulfide film. This film has been
known to capture and imbed airborne dirt. Breaking through this film
generates electrical noise. Because of this, fine silver contacts are not
used for low-level switching, such as audio circuits. Rather, fine silver
and silver alloy contacts are for use in circuits of 12 volts, 0.4 ampere, or
more.

"
I agree with Fred about Q2. That transistor is Germanium and measures strange on modern testers.  We are so used to Silicon that no one remembers that there was a Germanium transistor before Si. Either way these will have low forwward voltage. Mine measures about 0.1V and i thought its broken too.  But its old school and will show low Froward voltages.

[valley001]

Hi all,

I allowed the unit to operate for about 4 hours, and is supplying a voltage in the "correct" range more or less to 3-4 places after the decimal.  Ive found myself in the position of not having a volt meter with sufficient resolution to view the output voltage accurately.  I think a voltmeter upgrade is in my future.

This morning I discovered a cap on the current limiter has leaked electrolyte during the 4 hours it was operating.  This is disturbing to me because it tested fine on my component tester.  I think I may replace more electrolytic caps to avoid future issues.  For starters I plan to replace C1-5 on the HV mother board, C1, C4, C6, and C10 on the current limiter, C2 on the series pass, and C2 on the Aux Power board. 

Any thoughts on this plan?   I would not want to disturb the accuracy or linearity potential, I dont think any of these caps would effect this correct?