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Telequipment D34

Ondrej Pavelka
 

Hello to the group, this question is Tektronix related but it is not Tektronix per say. It is related to the subsidiary Telequipment.
I have this tiny cute battery operated scope called D34. Unfortunately there is one J-fet faulty and manual refers to it as Special TEL Spec

I found some parts lists of Telequipment part numbers and it says WN537A. WN537A is equally unobtainable and nor is the specification / datasheet. It is possible it was custom made by Siliconix in Swansea and there are no documents around from long lost factory.

Any suggestions what to try? I have put some J FET in there and it's not working too well. I get massive problems with blanking when Ch is exactly what this transistor is in charge of.
Any other ideas aside of gathering as many N jfets as possible and test and try them ?

Jim Tibbits
 

Any chance there is a table of typical voltages on this device? // figure
out how much current is flowing or biased cutoff//
circuit function amplifier/gate/....typical mpf102, drain current at zero
volts (gate to source) can range from 2 ma to 20 ma ..Likely units were
selected for closer range of drain current ...

Jim

On Sun, Jun 7, 2020 at 1:47 PM Ondrej Pavelka <info@...>
wrote:

Hello to the group, this question is Tektronix related but it is not
Tektronix per say. It is related to the subsidiary Telequipment.
I have this tiny cute battery operated scope called D34. Unfortunately
there is one J-fet faulty and manual refers to it as Special TEL Spec

I found some parts lists of Telequipment part numbers and it says WN537A.
WN537A is equally unobtainable and nor is the specification / datasheet. It
is possible it was custom made by Siliconix in Swansea and there are no
documents around from long lost factory.

Any suggestions what to try? I have put some J FET in there and it's not
working too well. I get massive problems with blanking when Ch is exactly
what this transistor is in charge of.
Any other ideas aside of gathering as many N jfets as possible and test
and try them ?



teamlarryohio
 

You might post the Tek 151-xxxx-xx part number if you have it.

Ondrej Pavelka
 

151-1076-00
151-1076-01

On Tue, 9 Jun 2020, 15:46 teamlarryohio, <larrys@...> wrote:

You might post the Tek 151-xxxx-xx part number if you have it.



Ondrej Pavelka
 

I have uploaded the schematics for D34. This J-fet is on page 5 it is a separate pdf.

I hope it helps

Jim Tibbits
 

stuck a schematic redrawn for tr302 in d34 folder...looks like a constant current regulator for the unblanking circuitry to me, but ...

Jim

Ondrej Pavelka
 

The problem I have with the random J-fet I used is following.

Scenario 1, channel 2 is OFF

I only get trace for high frequencies, on low frequencies it shrinks to
left side gradually up to the point I only see dot which moves up or down

Scenario 2 channel 2 is ON and no signal present

I get trace for low frequencies, then I get the problem mentioned above
with screen shrunk to one side and then if I am on high enough frequencies
I see the whole trace again.


I think what I am seeing is unblanking issue?

On Wed, 10 Jun 2020, 08:54 Jim Tibbits, <ab7vf1@...> wrote:

stuck a schematic redrawn for tr302 in d34 folder...looks like a constant
current regulator for the unblanking circuitry to me, but ...

Jim



Jim Tibbits
 

what I would do ...since tr104 is the same type, i would remove tr104 and
measure its Idss...Match Idss with measured random different fet ..replace
tr104 with original, replace tr302 with matched Idss fet
that should at least get you in the ball-park
(the same type fet is used in the D32 and the D61 if you know anyone who
has parts unit)

Jim

On Wed, Jun 10, 2020 at 2:09 AM Ondrej Pavelka <info@...>
wrote:

The problem I have with the random J-fet I used is following.

Scenario 1, channel 2 is OFF

I only get trace for high frequencies, on low frequencies it shrinks to
left side gradually up to the point I only see dot which moves up or down

Scenario 2 channel 2 is ON and no signal present

I get trace for low frequencies, then I get the problem mentioned above
with screen shrunk to one side and then if I am on high enough frequencies
I see the whole trace again.


I think what I am seeing is unblanking issue?




On Wed, 10 Jun 2020, 08:54 Jim Tibbits, <ab7vf1@...> wrote:

stuck a schematic redrawn for tr302 in d34 folder...looks like a constant
current regulator for the unblanking circuitry to me, but ...

Jim





David Tucker
 

Now that reminds me.

When I was repairing my Telequipment D61A, I needed the exact same JFET for the input amplifier - 151-1076-00.
I tried a few different JFETS, but the one that worked perfectly for that source follower was a J113. I bought 10, and most of them worked perfectly.

I know that this application is different, but if you have any J113s to hand, it might be worth a try.

Of course, a better way of doing it would be to follow Jim's advice - characterise TR104, then perhaps compare it with the datasheet for J113.

David

On Wed, Jun 10, 2020 at 02:56 PM, Jim Tibbits wrote:


what I would do ...since tr104 is the same type, i would remove tr104 and
measure its Idss...Match Idss with measured random different fet ..replace
tr104 with original, replace tr302 with matched Idss fet
that should at least get you in the ball-park
(the same type fet is used in the D32 and the D61 if you know anyone who
has parts unit)

Doug
 

For what it's worth I have plugged a WN537A/151-1076-00 from my D61 into a 577. Maybe will help in finding a replacement. Max Vds looks like about 50V
Photo is in the D34 folder of the Files section

Ondrej Pavelka
 

you guys are awesomest of the awesome. I have checked few of my J113 and
matched it by idss to the other WN fet and it works a charm!!!!

thanks so much!!

I now have fully functional D34, time to change the leaky lilac
electrolytics before they wreak the havoc to the pcbs. I was really sad
from my 2445b hybrid demise and this cheered me right up.

On Wed, Jun 10, 2020 at 9:09 PM Doug <dmeek@...> wrote:

For what it's worth I have plugged a WN537A/151-1076-00 from my D61 into a
577. Maybe will help in finding a replacement. Max Vds looks like about 50V
Photo is in the D34 folder of the Files section



Ondrej Pavelka
 

As much for don't fix what's not broken. When I was changing the caps on
the horizontal amp board I must have done some damage.

I have now doubled trace and I can't move the picture to the middle of the
screen. When it hits the 4th tile from the right it starts squashing. This
time it is not frequency dependent. It does it for all settings regardless.

https://photos.app.goo.gl/u3HWacuEEoD41HFn7

Time to go through it again :(

On Thu, 11 Jun 2020, 09:59 Ondrej Pavelka, <info@...>
wrote:

you guys are awesomest of the awesome. I have checked few of my J113 and
matched it by idss to the other WN fet and it works a charm!!!!

thanks so much!!

I now have fully functional D34, time to change the leaky lilac
electrolytics before they wreak the havoc to the pcbs. I was really sad
from my 2445b hybrid demise and this cheered me right up.


On Wed, Jun 10, 2020 at 9:09 PM Doug <dmeek@...> wrote:

For what it's worth I have plugged a WN537A/151-1076-00 from my D61 into
a 577. Maybe will help in finding a replacement. Max Vds looks like about
50V
Photo is in the D34 folder of the Files section



Jim Tibbits
 

well, at least it worked "once" ...save the jfet info in your bag o tricks,
it might come in handy

Jim

On Thu, Jun 11, 2020 at 3:45 AM Ondrej Pavelka <info@...>
wrote:

As much for don't fix what's not broken. When I was changing the caps on
the horizontal amp board I must have done some damage.

I have now doubled trace and I can't move the picture to the middle of the
screen. When it hits the 4th tile from the right it starts squashing. This
time it is not frequency dependent. It does it for all settings regardless.

https://photos.app.goo.gl/u3HWacuEEoD41HFn7

Time to go through it again :(

On Thu, 11 Jun 2020, 09:59 Ondrej Pavelka, <info@...>
wrote:

you guys are awesomest of the awesome. I have checked few of my J113 and
matched it by idss to the other WN fet and it works a charm!!!!

thanks so much!!

I now have fully functional D34, time to change the leaky lilac
electrolytics before they wreak the havoc to the pcbs. I was really sad
from my 2445b hybrid demise and this cheered me right up.


On Wed, Jun 10, 2020 at 9:09 PM Doug <dmeek@...> wrote:

For what it's worth I have plugged a WN537A/151-1076-00 from my D61 into
a 577. Maybe will help in finding a replacement. Max Vds looks like
about
50V
Photo is in the D34 folder of the Files section





Ondrej Pavelka
 

It did work and I fixed it now fully so it is all good now. It was just one
wire from the horizontal board that went loose.

On Fri, 12 Jun 2020, 05:09 Jim Tibbits, <ab7vf1@...> wrote:

well, at least it worked "once" ...save the jfet info in your bag o tricks,
it might come in handy

Jim

On Thu, Jun 11, 2020 at 3:45 AM Ondrej Pavelka <
info@...>
wrote:

As much for don't fix what's not broken. When I was changing the caps on
the horizontal amp board I must have done some damage.

I have now doubled trace and I can't move the picture to the middle of
the
screen. When it hits the 4th tile from the right it starts squashing.
This
time it is not frequency dependent. It does it for all settings
regardless.

https://photos.app.goo.gl/u3HWacuEEoD41HFn7

Time to go through it again :(

On Thu, 11 Jun 2020, 09:59 Ondrej Pavelka, <info@...>
wrote:

you guys are awesomest of the awesome. I have checked few of my J113
and
matched it by idss to the other WN fet and it works a charm!!!!

thanks so much!!

I now have fully functional D34, time to change the leaky lilac
electrolytics before they wreak the havoc to the pcbs. I was really sad
from my 2445b hybrid demise and this cheered me right up.


On Wed, Jun 10, 2020 at 9:09 PM Doug <dmeek@...> wrote:

For what it's worth I have plugged a WN537A/151-1076-00 from my D61
into
a 577. Maybe will help in finding a replacement. Max Vds looks like
about
50V
Photo is in the D34 folder of the Files section







David Tucker
 

That’s great news. You had us worried there, Ondrej.

Enjoy your little ‘scope.

David

On Fri, Jun 12, 2020 at 11:53 AM, Ondrej Pavelka wrote:
I fixed it now fully so it is all good now. It was just one
wire from the horizontal board that went loose.
Ondrej Pavelka <
info@...>
wrote:

As much for don't fix what's not broken. When I was changing the caps on
the horizontal amp board I must have done some damage.

I have now doubled trace and I can't move the picture to the middle of
the
screen.