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"Volts/Div" knob for Tek 2235 needed [ Tek part No : 366-2148-01]

donald collie
 

I only really need the clear plastic skirt on this knob [minimum], or two
complete knobs [maximum], as I can probably repair the other one, which has
a cracked skirt. Willing to pay for these. Probably also used on other 22xx
types.
Also : I replaced the chopper MOSFET in the psu with a NZ$1-60 generic
type. It gets very hot to my way of thinking - too hot to hold your finger
on the heatsink near it- does anyone know if an exact replacement is
necessary - perhaps a faster type with lower losses. The MOSFET`s molex
socket shows signs of being quite hot over some time [browning]
Thankyou in anticipation for your
reply.........................................................Donald ZL4GX

tom jobe <tomjobe@...>
 

One of the members of Tekscopes makes new replacement volt/div knob skirts for the 2235. I have bought some of them from him and they are very nice.
He also carries some hard to find good used/tested parts for the 2235 such as the main transformer (T948?), the high voltage multiplier (U975?), etc.
This link shows what he has in stock for sale on eBay at the moment, he must be out of those 2235 knob skirts temporarily.
https://www.ebay.com/sch/shockcore/m.html?item=273836542787&hash=item3fc1ee0b43%3Ag%3AHUcAAOSwZQRYf5YX&rt=nc&_trksid=p2047675.l2562
He is a great guy to do business with as his 100% eBay customer satisfaction rating shows.
I have bought several sets of his new replacement 2235 volt/div knob skirts and they work perfectly.
About he only way you can make a mess of the knob skirt replacement is to  use too much glue.
A few very tiny dabs of glue/epoxy at the smallest diameter of the knob register is all you need, and there is a notch that orients the skirt to the knob just like the original had.
The member name he uses on Tekscopes escapes me at the moment, but you can contact him through any of his eBay auction pages such as this page for his 2235 main transformers.
https://www.ebay.com/itm/Tektronix-120-1601-01-SwitchmodeTransformer-for-2213A-2215A-2235-Oscilloscope/273836542796?hash=item3fc1ee0b4c:g:bAQAAOSwnrJbfX~4
tom jobe...

On 5/24/2019 9:44 PM, donald collie wrote:
I only really need the clear plastic skirt on this knob [minimum], or two
complete knobs [maximum], as I can probably repair the other one, which has
a cracked skirt. Willing to pay for these. Probably also used on other 22xx
types.
Also : I replaced the chopper MOSFET in the psu with a NZ$1-60 generic
type. It gets very hot to my way of thinking - too hot to hold your finger
on the heatsink near it- does anyone know if an exact replacement is
necessary - perhaps a faster type with lower losses. The MOSFET`s molex
socket shows signs of being quite hot over some time [browning]
Thankyou in anticipation for your
reply.........................................................Donald ZL4GX

donald collie
 

Thankyou Tom, i`ll drop him a line..................Don

On Sat, May 25, 2019 at 6:43 PM tom jobe <tomjobe@...> wrote:

One of the members of Tekscopes makes new replacement volt/div knob
skirts for the 2235. I have bought some of them from him and they are
very nice.
He also carries some hard to find good used/tested parts for the 2235
such as the main transformer (T948?), the high voltage multiplier
(U975?), etc.
This link shows what he has in stock for sale on eBay at the moment, he
must be out of those 2235 knob skirts temporarily.

https://www.ebay.com/sch/shockcore/m.html?item=273836542787&hash=item3fc1ee0b43%3Ag%3AHUcAAOSwZQRYf5YX&rt=nc&_trksid=p2047675.l2562
He is a great guy to do business with as his 100% eBay customer
satisfaction rating shows.
I have bought several sets of his new replacement 2235 volt/div knob
skirts and they work perfectly.
About he only way you can make a mess of the knob skirt replacement is
to use too much glue.
A few very tiny dabs of glue/epoxy at the smallest diameter of the knob
register is all you need, and there is a notch that orients the skirt to
the knob just like the original had.
The member name he uses on Tekscopes escapes me at the moment, but you
can contact him through any of his eBay auction pages such as this page
for his 2235 main transformers.

https://www.ebay.com/itm/Tektronix-120-1601-01-SwitchmodeTransformer-for-2213A-2215A-2235-Oscilloscope/273836542796?hash=item3fc1ee0b4c:g:bAQAAOSwnrJbfX~4
tom jobe...








On 5/24/2019 9:44 PM, donald collie wrote:
I only really need the clear plastic skirt on this knob [minimum], or two
complete knobs [maximum], as I can probably repair the other one, which
has
a cracked skirt. Willing to pay for these. Probably also used on other
22xx
types.
Also : I replaced the chopper MOSFET in the psu with a NZ$1-60 generic
type. It gets very hot to my way of thinking - too hot to hold your
finger
on the heatsink near it- does anyone know if an exact replacement is
necessary - perhaps a faster type with lower losses. The MOSFET`s molex
socket shows signs of being quite hot over some time [browning]
Thankyou in anticipation for your
reply.........................................................Donald
ZL4GX





tom jobe <tomjobe@...>
 

Your question of how hot the heat sink gets near the MOSFET  Q9070 made me want to check a 2235 I had worked on just enough to get it to run.
This 2235 needed a lot of new power supply parts including the MOSFET Q9070 which was replaced with an ordinary IRF840 (8A, 500V) MOSFET.
After this 2235 had run for a half hour the heatsink was at 112 degrees F when checked next to the head of the screw that holds Q9070 onto the heatsink.
It was no problem to hold your finger on the heatsink at that temperature, and there was no visible evidence of heat on the MOSFET's Molex connector from this 2235's previous life.
The way I understand it, Q9070 chops up the rectified DC coming in from the line voltage as directed by the PWM chip U930 to create the 43 volt DC that powers the primary side of the transformer T948.
I believe the 43 volt supply's current limit is controlled by U930 using different values of R912 to actually set the current limit for the different models of oscilloscope in the 22XX family that use this same power supply architecture.
Getting back to your heat problem, it is hard to imagine that something is loading your 43 volt supply, and that the current limit is wrongly being set high enough to cause the temperature to be too high at Q9070, but I guess anything is possible.
I have had very good luck using the IRF840 MOSFET for Q9070, and with using the transistor TIP41C for Q947 and Q947, and I think those are the only three components on that heatsink plate.
tom jobe...

On 5/24/2019 9:44 PM, donald collie wrote:
I only really need the clear plastic skirt on this knob [minimum], or two
complete knobs [maximum], as I can probably repair the other one, which has
a cracked skirt. Willing to pay for these. Probably also used on other 22xx
types.
Also : I replaced the chopper MOSFET in the psu with a NZ$1-60 generic
type. It gets very hot to my way of thinking - too hot to hold your finger
on the heatsink near it- does anyone know if an exact replacement is
necessary - perhaps a faster type with lower losses. The MOSFET`s molex
socket shows signs of being quite hot over some time [browning]
Thankyou in anticipation for your
reply.........................................................Donald ZL4GX

tom jobe <tomjobe@...>
 

Whoops!
I made a mistake in the last sentence, it should read:
'I have had very good luck using the IRF840 MOSFET for Q9070, and with using the transistor TIP41C for _Q946_ and Q947, and I think those are the only three components on that heatsink plate'
tom jobe...

On 5/25/2019 3:51 PM, tom jobe via Groups.Io wrote:
Your question of how hot the heat sink gets near the MOSFET  Q9070 made me want to check a 2235 I had worked on just enough to get it to run.
This 2235 needed a lot of new power supply parts including the MOSFET Q9070 which was replaced with an ordinary IRF840 (8A, 500V) MOSFET.
After this 2235 had run for a half hour the heatsink was at 112 degrees F when checked next to the head of the screw that holds Q9070 onto the heatsink.
It was no problem to hold your finger on the heatsink at that temperature, and there was no visible evidence of heat on the MOSFET's Molex connector from this 2235's previous life.
The way I understand it, Q9070 chops up the rectified DC coming in from the line voltage as directed by the PWM chip U930 to create the 43 volt DC that powers the primary side of the transformer T948.
I believe the 43 volt supply's current limit is controlled by U930 using different values of R912 to actually set the current limit for the different models of oscilloscope in the 22XX family that use this same power supply architecture.
Getting back to your heat problem, it is hard to imagine that something is loading your 43 volt supply, and that the current limit is wrongly being set high enough to cause the temperature to be too high at Q9070, but I guess anything is possible.
I have had very good luck using the IRF840 MOSFET for Q9070, and with using the transistor TIP41C for Q947 and Q947, and I think those are the only three components on that heatsink plate.
tom jobe...




On 5/24/2019 9:44 PM, donald collie wrote:
I only really need the clear plastic skirt on this knob [minimum], or two
complete knobs [maximum], as I can probably repair the other one, which has
a cracked skirt. Willing to pay for these. Probably also used on other 22xx
types.
Also : I replaced the chopper MOSFET in the psu with a NZ$1-60 generic
type. It gets very hot to my way of thinking - too hot to hold your finger
on the heatsink near it- does anyone know if an exact replacement is
necessary - perhaps a faster type with lower losses. The MOSFET`s molex
socket shows signs of being quite hot over some time [browning]
Thankyou in anticipation for your
reply.........................................................Donald ZL4GX



satbeginner
 

My 2 cents: a while back I repaired a 2215A and used the same IRF as a replacement.

I added a small 12V fan (don't remember if it was 60 or 70 mm, but the homes were already there), and also because the location for the diode and the small connector were already there on the PCB.

If I remember well Tek used only one rectifier diode and a capacitor, the result was around 9V DC that made the 12V fan run nice and quiet, but it kept everything cool.

I believe the fan was only put in with certain 21xx models because of the higher 43V current, but it worked great with the 2215A.

Succes,

Leo

Jared Cabot
 

I have done a number of upgrades as discussed in this thread on my 2235.

I made a video with all the part numbers and info needed, including the service upgrade on the PSU section, capacitor replacement, fan install, and 510K focus resistor replacements.

Someone might find it useful I guess...

https://www.youtube.com/watch?v=lrXCVg6T-ek

donald collie
 

Thanks Leo, and Jared - yes a fan would make all the difference.
Unfortunately the gentleman concerened no longer makes the 22xx Volts/Div
knobs, so I`m not sure exactly where to get two of those knob skirts. Does
anybody have a parts mule 22xx `scope, and can help? Nice video Jared -
your `scope is in nice order.
Cheers!...........................................................Don

On Sun, May 26, 2019 at 7:23 PM Jared Cabot <jaredcabot@...> wrote:

I have done a number of upgrades as discussed in this thread on my 2235.

I made a video with all the part numbers and info needed, including the
service upgrade on the PSU section, capacitor replacement, fan install, and
510K focus resistor replacements.

Someone might find it useful I guess...

https://www.youtube.com/watch?v=lrXCVg6T-ek