Author Topic: Fluke 332D repair..still sorting issues (Read 14172 times)

valley001 · « **on:** March 04, 2019, 06:51:56 am »

I was really hoping I would not have to repair this, but such is the risk of buying old used equipment like this untested. I am fairly green with repairing electronics and this would probably be my most challenging project yet.

This 332D is non functional. It does not output voltage, I get -1.24v no matter the settings on the dials . Upon visual inspection I found the following:

-Q4 and Q8 missing from the differential amplifier board (that cant be good).

-Current limiter board shows evidence of heating in the vicinity of Q1 and Q2, especially at R3.

-Some evidence of heating on the pre regulator board.

On the plus side my example does have the extender card still in place.

I have not done any voltage measurements yet, that will probably have to wait until next weekend unfortunately. I am hoping for some ideas on how to proceed. I am assuming at the very least I need to find Q4 and Q8 for the differential amp board.

One other thing I notice is the decimal LEDs, only the 10v range decimal lights. When switching through the ranges 100v and 1000v the decimals do not light for those ranges.

wictor · « **Reply #1 on:** March 04, 2019, 04:07:22 pm »

Hi,

Fluke voltage reference seems to be hot topic currently... You could start by reading following threads:
https://www.eevblog.com/forum/repair/fluke-3330b-no-output-but-relays-clicks-some-life-in-it/
https://www.eevblog.com/forum/repair/fluke-332d-initial-power-up-paper-caps-in-hv-motherboard/

Wictor

wictor · « **Reply #2 on:** March 04, 2019, 04:11:27 pm »

Quote

-Current limiter board shows evidence of heating in the vicinity of Q1 and Q2, especially at R3.
-Some evidence of heating on the pre regulator board.

I would say this is normal for these units.

Quote

One other thing I notice is the decimal LEDs, only the 10v range decimal lights. When switching through the ranges 100v and 1000v the decimals do not light for those ranges.

Most of the units have this problem, it's easy to replace broken bulbs with LEDs.

Wictor

valley001 · « **Reply #3 on:** March 04, 2019, 04:39:50 pm »

I started taking readings on the semiconductors on the current limiter board, since this one seems to have taken a beating. Tests done in circuit.

Q7- Reads in both directions B-E

Q1 and Q2- Ive not tested these larger transistors before, but Q1 tests in both directions on one side. Q2 also tests suspiciously.

C6 looks like its toast.

Edit to add- CR6 is missing from the pre regulator board.

Man what a bummer.

Edit to add:

OK, I think I will focus on the pre regulator board first. I managed to test all of the transistors and they seem fine I think. Some (Motorola SM4144) have hFE in the mid 30s-40s. Some diodes test strangely, many of them read both ways in circuit. Ill lift those and test again. In the mean time I will find a replacement for CR6, 1N4822 (could I use a 1n4005 here?)

valley001 · « **Reply #4 on:** March 04, 2019, 11:57:05 pm »

So CR6 on the pre regulator board is associated with the K1 power supply, which engages pin 7-8 to the "pre regulator bridge." I think the pre regulator bridge leads to the "pre regulator bridge attenuator."

Am I correct in my assumption that the entire device would fail to operate if K1 does not engage?

kawal · « **Reply #5 on:** March 05, 2019, 03:13:37 am »

I just revived my completely dead 3330B.

Here is what method I used to trace the source of failure:

Remove all boards to inspect the boards for visual inspection and bad electrolytic capacitor via ESR. I found only 2 bad ones but will replace all of them when my part arrive. These things are now over 45 years old.
Check all diods and transistors for conductivity. Please check the Power boards as first priority - I found 1 broken transistor and later zener diod.
Pull any socketed transistors and check for Beta loss. Another member ( Frank ) mentioned this and I was not aware that its a thing to worry about. But found 1 transistor with good diod test but with no gain.

Look at the schematic for your unit . It is possible to test most cards outside the unit by providing the right voltages to the cards. - Most cards its 1 or 2 voltages for power.
My unit was completely dead too but now its working with only a few days effort. It might take less or more time but its worth restoring these awesome units.

In my unit the pre driver was suspect as it had burnt wires. At the end it turned out the current sense resistor at the emiter of the driver transistor had bad contact with the board due to thermal cycling. After re soldering that resistor (and earlier replacing a transistor with 0 HFE ) the board worked.

Good luck and be careful. The units can output deadly voltages.

Maciej

kawal · « **Reply #6 on:** March 05, 2019, 03:18:45 am »

Yes the device will not output voltages if K1 is off.
But lights should turn on the front panel even if K1 is off.
The decimal ~~points are bulbs~~ are LEDs in the 332D but the older diods could be dead due to the high current of 16mA used for such early diods. My unit had bulbs with only only had 1 working bulb. Now all replaced with White LEDs. In the 3330B the bulbs get power from -25V so a 2K resistor and a white LEDs I used 0.5W leds running at 11mA. They are super bright at the 30mW power. Use in min 0.5W resistors for the diods.
Make sure all the power rails are there - the low voltage ones (+25, -15, +35, -35 , +12, -12 )

On my unit the contacts on K1 where not in best shape so i took them off the relay for a good cleaning and polishing before putting back in the unit.

Quote from: valley001 on March 04, 2019, 11:57:05 pm

So CR6 on the pre regulator board is associated with the K1 power supply, which engages pin 7-8 to the "pre regulator bridge." I think the pre regulator bridge leads to the "pre regulator bridge attenuator."

Am I correct in my assumption that the entire device would fail to operate if K1 does not engage?

kawal · « **Reply #7 on:** March 05, 2019, 03:51:28 am »

These are general purpose diods and the ones you mentioned will be fine - I would change all 4 to the same type in the bridge.
If the transistor conducts in both ways its bad, assuming its out of circuit. Q7 should not conduct both ways even in circuit.

Quote from: valley001 on March 04, 2019, 04:39:50 pm

I started taking readings on the semiconductors on the current limiter board, since this one seems to have taken a beating. Tests done in circuit.

Q7- Reads in both directions B-E

Q1 and Q2- Ive not tested these larger transistors before, but Q1 tests in both directions on one side. Q2 also tests suspiciously.

C6 looks like its toast.

Edit to add- CR6 is missing from the pre regulator board. Man what a bummer.

Edit to add:

OK, I think I will focus on the pre regulator board first. I managed to test all of the transistors and they seem fine I think. Some (Motorola SM4144) have hFE in the mid 30s-40s. Some diodes test strangely, many of them read both ways in circuit. Ill lift those and test again. In the mean time I will find a replacement for CR6, 1N4822 (could I use a 1n4005 here?)

valley001 · « **Reply #8 on:** March 05, 2019, 04:11:35 am »

kawal- I appreciate your responses, thank you. Sometimes I get ahead of myself...I need to study the circuit more carefully so I understand how the boards interact with each other.

I will check voltages this weekend, along with the other suggested tests in the troubleshooting portion of the manual.

In the mean time, the differential amp board is missing Q4 and Q8...any idea on a modern replacement for these? The originals seem to be unobtanium.

texaspyro · « **Reply #9 on:** March 05, 2019, 05:32:25 am »

These units are famous for bad electrolytics on the main board. It is one of the few devices where I would recommend replacing all of them.

beanflying · « **Reply #10 on:** March 05, 2019, 05:50:42 am »

Quote from: texaspyro on March 05, 2019, 05:32:25 am

These units are famous for bad electrolytics on the main board. It is one of the few devices where I would recommend replacing all of them.

332D only or the 335D as well? My recent acquisition touch wood looks good but I haven't cracked the case yet.

texaspyro · « **Reply #11 on:** March 05, 2019, 06:14:57 am »

Quote from: beanflying on March 05, 2019, 05:50:42 am

Quote from: texaspyro on March 05, 2019, 05:32:25 am
These units are famous for bad electrolytics on the main board. It is one of the few devices where I would recommend replacing all of them.

332D only or the 335D as well? My recent acquisition touch wood looks good but I haven't cracked the case yet.

Assume all of them are guilty... I pulled around 10 bad caps off of my 332D.

kawal · « **Reply #12 on:** March 05, 2019, 03:30:12 pm »

Valley
I would replace Q4 and Q6 together as a pair. Something like KSC1008YBU will work just fine are a cheap (34cents each). NPN 60V moderate gain and moderate bandwidth.
You could also use KSD1616AYTA for both Q4, Q6 or just for Q8, one type would make it easier. Thats what I would use ( original 60V, 1A, 0.8W device) .

Maciej

Quote from: valley001 on March 05, 2019, 04:11:35 am

kawal- I appreciate your responses, thank you. Sometimes I get ahead of myself...I need to study the circuit more carefully so I understand how the boards interact with each other.

I will check voltages this weekend, along with the other suggested tests in the troubleshooting portion of the manual.

In the mean time, the differential amp board is missing Q4 and Q8...any idea on a modern replacement for these? The originals seem to be unobtanium.

valley001 · « **Reply #13 on:** March 05, 2019, 06:29:04 pm »

I made the same assumption on Q8, the unmarked one makes the most sense.

OK so:

Q4 and 6 use: KSC1008YBU

Q8 use: KSD1616AYTA

Ill order 1n4005G for the rectifier diodes.

I am hoping Q1 and Q2 are good on the current limiter, I have not tested them out of circuit yet.

Do you have a suggestion for Q7 on the current limiter board?

kawal · « **Reply #14 on:** March 05, 2019, 08:58:54 pm »

Valley
Looking at the schematic (and confirmed in section 3-41 in the manual) the Q7 on the current limit board seems to be an LED controller .It blinks the the LED when current limit happens.
Based on that I would let you pick any NPN with Vce>=60V and Ic >= 200ma
Maciej

valley001 · « **Reply #15 on:** March 06, 2019, 05:41:21 pm »

Had some time to test transistors this morning, here are the results all out of circuit:

Pre Regulator:

Q1- BJT-NPN, hFE 178, Vf 542mV

Q2- BJT-NPN, hFE 96, Vf 651mV

There two look good no?

Current Limiter:

Q1- BJT-NPN, hFE 149, Vf 618mV

Q2- BJT-NPN, hFE 5, Vf 36mV

Looks like Q2 is toast. I see NOS available so thats a plus.

I think I am going to replace the electrolytic on the pre regulator and the diodes CR6-9 and then call it good. Ill try to power up again after doing the voltage checks and installing the replacements for diff amp Q4 and Q8.

I did do the resistance checks on each readout step, these all seem good.

kawal · « **Reply #16 on:** March 06, 2019, 05:50:12 pm »

Q2 is definitely toast. New old stock makes it easier but some of the current transistors should be more reliable.

valley001 · « **Reply #17 on:** March 06, 2019, 06:05:49 pm »

Quote from: kawal on March 06, 2019, 05:50:12 pm

Q2 is definitely toast. New old stock makes it easier but some of the current transistors should be more reliable.

Which model would be a good equivalent?

I did the resistance checks on the pre reg board and aux power. Current limiter pin 1 and 3 to sense read over 1 meg. Q2 is out of circuit so perhaps that is the cause.

valley001 · « **Reply #18 on:** March 07, 2019, 03:53:19 pm »

Man someone was really into this thing before I. Inspecting the boards it looks like the chopper FET was removed at some point for some reason. . It tests fine. Many resistors and caps also show evidence of having been removed. I tested a bunch of electrolytic caps and all the ones I tested seem fine on my little component tester.

I tested every other socketed transistor in this thing, they all seem good.

List of needed repairs so far:

Bridge in the relay PSU on the pre regulator board
Q2 on the current limiter
Install missing Q4 and Q8 on the amp board
Replace two dead decimal LEDs

Hopefully I will have voltage after these repairs. I am still concerned with the resistance readings I am getting between sense and pins 1 and 3 of the current limiter board.

kawal · « **Reply #19 on:** March 07, 2019, 11:24:17 pm »

Dont worry about current limiter The schematic has 2 pages and 1 and 3 are the +35V and -35V lines that go to may devices. Check out all the items connected to the board internally

Fred_47 · « **Reply #20 on:** March 08, 2019, 05:56:54 am »

Quote from: valley001 on March 04, 2019, 06:51:56 am

-Current limiter board shows evidence of heating in the vicinity of Q1 and Q2, especially at R3.

One other thing I notice is the decimal LEDs, only the 10v range decimal lights. When switching through the ranges 100v and 1000v the decimals do not light for those ranges.

The 332 shares a lot (almost all) circuitry with the 335. However there seems to be several versions over the years so compare any schematics to your circuit before taking any action.

The K1 relay is a safety switch that allows the high voltage to be energized only when all the cards are installed and the covers are in place. It is slightly delayed to allow K2 to pick up first. (A diode & capacitor circuit.)

The decimal point LEDs on my 335D all failed about 6 months after I got it working and when I checked the circuit I found that the 2.4K resistor (R3) on the current limiter board was burnt black. This is the ±35V supply. The lamp supply is tapped before the regulating transistor. My notes indicate that this voltage is about 60 V and I'm driving the LEDs to about 20mA.

The original circuit with filament lamps had 3 resistors in series and the circuit card had traces in place for all 3. I replaced the LEDs (had to file down the diameter to fit) and used 2- 1500, 2 Watt resistors to spread out the heat & compensate for the higher ambient temp. BTW, the LEDs are held in place by single pin 'sockets' on the wiring. No need to unsolder anything except the failed resistor and jumper on the card. (At least that was the case on mine.)

Also note that all of the circuitry can be energized up to 1100V WRT the chassis so double/tripple check your replacement LED installation. The grommets and heat shrink are important.

I've also checked all of the capacitors and replaced most that were questionable. So far I've replaced about 15% of the caps. Someone before me had replaced many of the larger electrolitics. I suspect that Fluke gave it an updating the last time it was calibrated in 1992 as there seems to be a mix of old & new cards and components. (The oldest date code I've found is 1980 IIRC)

Here's a picture of the card before the failure. (I can't see the full part number but I think it's 354266, it's A5A6 in the parts list) You can see the traces and holes for the other resistors. I eventually replaced the blue cap (and most 'blue' caps on the other boards) and a one of the silver (Sprague) ones. Also, for what it's worth, a spreadsheet that I made as I checked the caps, the 1971 version of the power supply & the 1978 version with my modification. It may not match your unit.

valley001 · « **Reply #21 on:** March 08, 2019, 04:53:36 pm »

I did lift all of those 2 watt resistors and test them, since some obviously got hot. On mine, R3 is a 2.7K 2 watt resistor and tests pretty close. I guess this resistor is dissipating a lot of heat?

Q2 was toast (see above) so I wonder what sort of mayhem that may have caused.

I lifted the big electrolytic caps and they all test fine on my component tester, however I know the small tester is not really capable of testing these up to their operating conditions. I have had a cap (obviously bad) test fine on the component tester in the past.

Ill recap the whole thing once I can get some life out of it.

valley001 · « **Reply #22 on:** March 10, 2019, 01:12:52 am »

Its been a somewhat disappointing day.

-Installed new bridge for the relay PSU on pre regulator board
-Installed Q4, Q6, and Q8 on the amp board
-Installed new LEDs for the decimals

I was hoping with the relay PSU now functional and the missing transistors installed in the amp board I would get some sign of life from this thing, but no. Completely the same behavior when the unit is turned to "operate." I get 1.22v ish no matter the range or readout setting. The new LEDs work great so at least thats something

One thing I know is bad and has not been replaced is Q2 on the current limiter board. It has low hFE so figured it may not have a large effect on the function of the overall unit (correct, incorrect?).

Before cleaning the bench for the day I took voltage readings per 4.16 in the manual. Hoping someone may see something I dont/cant. I do see collector Q8 on the reference supply board is very high. Hoping that is not too ominous. I appreciate all the responses so far, hoping someone has some idea where I should go next.

Oh. On thing I have noticed is a intermittent buzzing sound (60hz maybe) from the HV mother board area. It comes and goes, but I have not isolated it to a specific component or to see if a specific relay energizes when it happens (dont want to stick my ears too close!) . Does not appear to be coming from the transformer.

I am absolutely determined to get this thing going.

Aux Power Board

Pin 10 24.9v
Pin 9 -14.86v

Current Limiter

Pin 1 -35v
Pin 3 37.4v

Range Cal

sense to red test point 15.06v

Reference Supply

Collector Q1 45v (Should be 26-35v) Maybe l need to look at R19 or further up?

Rear Bulkhead Resistor

Yellow lead 748v

Series Pass

Collector Q8 137.5v

kawal · « **Reply #23 on:** March 10, 2019, 05:10:57 am »

Well that is some progress. Aux power and power on current limit board look good. Remember to check the pre regulator supply as well.
That board cause some issues for me . The Mica/metal foil current sense resistor had bad solder joints. Basically causing so weird over current condition. Check the board out of the chassis.

Are the decimals also working now ?

Maciej

valley001 · « **Reply #24 on:** March 10, 2019, 05:20:15 am »

Decimals are working now. I am not sure how to check the pre regulator board out of chassis. Which resistor is the current sense?

Unrelated: Checking resistance per 4-57 on the current limiter I still get some odd results, like 500K between pins 1 and sense and 3 and sense.

I guess I am shooting in the dark now.

Quote from: kawal on March 10, 2019, 05:10:57 am

Well that is some progress. Aux power and power on current limit board look good. Remember to check the pre regulator supply as well.
That board cause some issues for me . The Mica/metal foil current sense resistor had bad solder joints. Basically causing so weird over current condition. Check the board out of the chassis.

Are the decimals also working now ?

Maciej


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Author Topic: Fluke 332D repair..still sorting issues (Read 14172 times)

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