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577 curve tracer 177 test fixture current per division troubleshoot

DW
 

I have made a post in the past about a problem I am having with the 177 test fixture. The problem is when I select anywhere between 0.1A 0.2A 0.5A the display goes to a dot as if I turned the collector all the way down, I had reason to suspect the current per division selector had dead spots at which maybe it wasn't properly making contact. I was suggested to use contact cleaner which I have done recently and worked the cleaner on the contacts well without drenching anything else to much. Upon further testing I found the settings between 0.1 0.2 and 0.5A per division still appears dead. Out of curiosity I decided to probe the resistors soldered on the switch with a ohm meter but I don't observe what might be bad resistors.

I am now checking the switch contacts if they might be bad. The current per division switch is about 3 layers deep, the top contacts are easy to check but the others sandwiched between is more difficult. I realize there is a contact which is constantly in contact with the inner ring and then a bar which slides under specific contacts when the switch is moved. I just need to find the other contacts which constantly slide on the inner ring and probe that and the contacts which are touching the contact bar to see if the contacts in the problem area are in fact working.

DW
 

In the process of troubleshooting the current per division switch on the 177, I recall the 577 has had a previous issue where its collector supply will not go to 0 volts even at 6.5V collector volts. With no fixture installed I powered on the curve tracer with a glowing yellow light which is collector supply disabled. I find the volts per division above 0.5V the trace is a dot but below 0.5 volts per division a line appears and becomes longer horizontally until it is 2 divisions long at the most sensitive voltage scale. I try adjusting the collector supply and it does nothing, doesn't get longer or shorter.

Interesting, when I select 25 collector volts with no fixture installed the yellow disabled collector voltage goes out and I can adjust the collector voltage making the horizontal line longer or shorter on the display, doesn't seem right, I didn't crank it all the way up and I didn't leave it like that for long.. All the other collector voltage modes properly disable the collector with no test fixture except 25V

Conclusion, this 577 has some problems!

 

Hi DW,

The 577, unlike the 575 and 576, has a nice feature that reduces the intensity when the collector voltage is reduced to zero and the beam becomes a dot, rather than a horizontal line, on the CRT, This feature is designed to prevent the phosphor from being burned.

The 577 issue you mention where a 577 collector supply will not go to 0 volts even at 6.5V collector volts was a problem with a specific 577, and not how 577s work.

I do agree that it sounds like your 577 has some problems but which problems are due to the missing 177 is hard to say.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of DW
Sent: Wednesday, April 22, 2020 2:36 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 577 curve tracer 177 test fixture current per division troubleshoot

In the process of troubleshooting the current per division switch on the 177, I recall the 577 has had a previous issue where its collector supply will not go to 0 volts even at 6.5V collector volts. With no fixture installed I powered on the curve tracer with a glowing yellow light which is collector supply disabled. I find the volts per division above 0.5V the trace is a dot but below 0.5 volts per division a line appears and becomes longer horizontally until it is 2 divisions long at the most sensitive voltage scale. I try adjusting the collector supply and it does nothing, doesn't get longer or shorter.

Interesting, when I select 25 collector volts with no fixture installed the yellow disabled collector voltage goes out and I can adjust the collector voltage making the horizontal line longer or shorter on the display, doesn't seem right, I didn't crank it all the way up and I didn't leave it like that for long.. All the other collector voltage modes properly disable the collector with no test fixture except 25V

Conclusion, this 577 has some problems!





--
Dennis Tillman W7PF
TekScopes Moderator

DW
 

Thanks for the reply.

Could anyone with a 577, if willing, attempt the 25V collector test with no fixture installed to see if the yellow disabled collector goes out? I assume with no fixture the collector should be disabled regardless what voltage setting.

DW
 

I used a LCR meter set to Z with a voltage level set to 0.3 volts. With the test fixture taken apart I connected one probe to TP617 which is next to the plug interface of the fixture with Q626 printed right next to it and a disk capacitor, I put the other probe on S640 where the thick blue and white wire connects to it. In the 177 schematic it looks like probing between these locations can get an idea of the resistance behavior as I move S630 Current per division around. I have another 177 test fixture which is broken which I compared to to, here are my results

177 A is a broken test fixture I have to test against
177 B is the test fixture I am using but when current per division 0.5A 0.2A and 0.1A selections not working

If you look at the tests results below you will find a clear difference between the measurements of 177A and 177B at 0.5A 0.2A 0.1A, A measures 0.25 ohms while B is measuring in mega ohms, something is definitely going open on the switch! No wonder my read out disappears when selecting between 05A to 0.1A. I am wondering how difficult it is to transplant the switch from the broken 177 test fixture to the working one, would this disturb the calibration I wonder causing issues with accurate readings?

Selection Reading from 177 A Reading from 177 B
======= ================ =============
2A 0.154 ohm 0.230 ohm
1A 0.161 ohm 0.222
.5A 0.258 ohm *2.74 m ohm*
.2A 0.247 ohm *2.74 m ohm*
.1A 0.251 ohm *2.73 m ohm*
50mA 1.146 ohm 1.245 ohm
20mA 1.144 ohm 1.240 ohm
10mA 1.142 ohm 1.244 ohm
5mA 10.197 ohm 10.22 ohm
2mA 10.189 ohm 10.22 ohm
1mA 10.192 ohm 10.22 ohm
.5mA 199.65 ohm 200.4 ohm
.2mA 199.64 ohm 200.4 ohm
.1mA 199.64 ohm 200.4 ohm
50uA 1.9961 k 2.011 k ohm
20uA 1.9961 k 2.011 k ohm
10uA 1.9961 k 2.011 k ohm
5uA 19.971 k 20.04 k ohm
2uA 19.970 k 20.04 k ohm
1uA 19.971 k 20.04 k ohm
.5uA 196.80 k 196.3 k ohm
.2uA 196.80 k 196.3 k ohm
.1uA 196.80 k 196.3 k ohm
50nA 991k 955 k ohm
20nA 991k 955 k ohm
10nA 991k 955 k ohm
5nA 1.15m 1.1 m ohm
2nA 1.15m 1.1 m ohm

David Berlind
 

should I assume, based on this last note, that having someone else
independently run the 25V collector test on their 577 is no longer needed?
I have a 577 in storage that I've earmarked for Dennis T's Eico 667 mod. I
haven't even turned it on since acquiring it.

On Thu, Apr 23, 2020 at 12:07 PM DW <wilson2115@...> wrote:

I used a LCR meter set to Z with a voltage level set to 0.3 volts. With
the test fixture taken apart I connected one probe to TP617 which is next
to the plug interface of the fixture with Q626 printed right next to it and
a disk capacitor, I put the other probe on S640 where the thick blue and
white wire connects to it. In the 177 schematic it looks like probing
between these locations can get an idea of the resistance behavior as I
move S630 Current per division around. I have another 177 test fixture
which is broken which I compared to to, here are my results

177 A is a broken test fixture I have to test against
177 B is the test fixture I am using but when current per division 0.5A
0.2A and 0.1A selections not working

If you look at the tests results below you will find a clear difference
between the measurements of 177A and 177B at 0.5A 0.2A 0.1A, A measures
0.25 ohms while B is measuring in mega ohms, something is definitely going
open on the switch! No wonder my read out disappears when selecting between
05A to 0.1A. I am wondering how difficult it is to transplant the switch
from the broken 177 test fixture to the working one, would this disturb the
calibration I wonder causing issues with accurate readings?

Selection Reading from 177 A Reading from 177 B
======= ================ =============
2A 0.154 ohm 0.230 ohm
1A 0.161 ohm 0.222
.5A 0.258 ohm *2.74 m ohm*
.2A 0.247 ohm *2.74 m ohm*
.1A 0.251 ohm *2.73 m ohm*
50mA 1.146 ohm 1.245 ohm
20mA 1.144 ohm 1.240 ohm
10mA 1.142 ohm 1.244 ohm
5mA 10.197 ohm 10.22 ohm
2mA 10.189 ohm 10.22 ohm
1mA 10.192 ohm 10.22 ohm
.5mA 199.65 ohm 200.4 ohm
.2mA 199.64 ohm 200.4 ohm
.1mA 199.64 ohm 200.4 ohm
50uA 1.9961 k 2.011 k ohm
20uA 1.9961 k 2.011 k ohm
10uA 1.9961 k 2.011 k ohm
5uA 19.971 k 20.04 k ohm
2uA 19.970 k 20.04 k ohm
1uA 19.971 k 20.04 k ohm
.5uA 196.80 k 196.3 k ohm
.2uA 196.80 k 196.3 k ohm
.1uA 196.80 k 196.3 k ohm
50nA 991k 955 k ohm
20nA 991k 955 k ohm
10nA 991k 955 k ohm
5nA 1.15m 1.1 m ohm
2nA 1.15m 1.1 m ohm



DW
 

I would say to have someone independently run a test on their 577 is still desired, though if they are willing and at their own convenience.

I am in the process where I am thinking about transplanting the current per division switch from a donor 177 but their serial numbers are different

The donor 177 is B052747
The 177 that will get the replacement part is B020417

I have looked at both switches and they appear to look the same with the same connections and similar resistors with similar placements. Looking at the table above the values are only slightly different. I would then conclude that replacement should be fine.

Dave Casey
 

Well of course their serial numbers are different.
If you're worried about it, the manual should tell you the serial number
effectivity for any component changes.

Dave Casey

On Thu, Apr 23, 2020 at 2:12 PM DW <wilson2115@...> wrote:

I would say to have someone independently run a test on their 577 is still
desired, though if they are willing and at their own convenience.

I am in the process where I am thinking about transplanting the current
per division switch from a donor 177 but their serial numbers are different

The donor 177 is B052747
The 177 that will get the replacement part is B020417

I have looked at both switches and they appear to look the same with the
same connections and similar resistors with similar placements. Looking at
the table above the values are only slightly different. I would then
conclude that replacement should be fine.




Eric
 

I can run the measurement I have an (as far as I know) good 577 though my 177 is in need of a looking cap before I can use it.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of DW
Sent: Thursday, April 23, 2020 3:12 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 577 curve tracer 177 test fixture current per division troubleshoot

I would say to have someone independently run a test on their 577 is still desired, though if they are willing and at their own convenience.

I am in the process where I am thinking about transplanting the current per division switch from a donor 177 but their serial numbers are different

The donor 177 is B052747
The 177 that will get the replacement part is B020417

I have looked at both switches and they appear to look the same with the same connections and similar resistors with similar placements. Looking at the table above the values are only slightly different. I would then conclude that replacement should be fine.

DW
 

I started to look at taking the switch out of the 177 fixture of the donor and so far this is appearing the be a nightmare of a task.

It looks like everything is built on top of other things, in order to get to the switch most of the fixture has to be completely disassembled. I wonder if anyone else has undertaken the task of working on a 177 test fixture?

On the manual it states to just simply remove the knob which is easy enough, and then the hex bolts which one side is not so hard to get at but other is way back in there. Finally desolder the leads from the switch however the front plate of the fixture is in the way for some of the leads.

I notice there is a plate over top of the fixture, it would be nice if I could just remove the front plate and remove the nuts for the switch. Wish I could just take out a few screws and out the board comes and then I can enjoy the working current division ranges along with my sanity

teamlarryohio
 

I just fired mine up on 25V with the front porch unplugged. No yellow
light.
-ls-

DW
 

Interesting, perhaps what I am experiencing isn't actually a defect.

Chuck Harris
 

If the porch switch isn't activated the yellow light
will come on... regardless of the collector voltage setting.

Also, the collector voltage will be disabled.

Most of the porch covers were lost in the first week of
operation, as we are all engineers, and know better than
to stick our fingers in there, and the covers get in the
way of real work.

So, jamb a piece of wood, or plastic in the hole where
the porch safety prong actuates the switch and the yellow
light will go off.

-Chuck Harris

DW wrote:

Interesting, perhaps what I am experiencing isn't actually a defect.



teamlarryohio
 

I was speaking of unplugging the whole 177. My DUT cover interlock got
jumpered years ago.
-ls-

Chuck Harris
 

Ok, I wasn't paying enough attention to the thread.

The yellow light is switched from several sources. The first, and most
obvious is the HV enable signals for the deadly HV ranges... which comes
from the porch.

The second is Q588 on the collector supply board. Notice that Q588
is involved with two 1uf tantalum caps, C586 and C587. You might want
to look at them. THe board is littered with similar tantalum caps that
are by now often found leaking their guts out all over the circuit board.

The electrolyte is sulfuric acid, and very conductive, and very corrosive.

-Chuck Harris

teamlarryohio wrote:

I was speaking of unplugging the whole 177. My DUT cover interlock got
jumpered years ago.
-ls-