#86761

Hi everyone,

I have just acquired this scope which was sold as not powering on. Once opened up I spotted that RT901 which sits on board A6 had a hole in it. I also measured it at 15ohms out of circuit.

According to the service manual this is a 100ohm thermal resistor, 10%, NTC. However, I am having problems finding a replacement in the UK. Is this part known under a different name?

I've taken a photo which I will add to the site.

Any help greatly appreciated.

Thanks

Alex

Tom Jobe

#86766

开云体育

Hi Alex,

I have a good 2235 A6 board that has been removed from a scope, and RT901 measures 15 Ohms in circuit.

The component has no other markings (of use) other than "10 Ohm" (where Ohm is the Ohm symbol).

The A6 schematic shows it as a "10 ohm" part as well.

A?look around the Mouser web site suggests that it might be called an "NTC?thermistor".

Look at this link:

There are links to the datasheets for most of the thermistors, and I would guess that you could figure out the amperage backwards from the physical size of the?RT901 you have.

There is about 20 mm of vertical room under the plastic cover for the thermistor, but?there is room to lay?it over a bit to get some extra space.

I?would consider putting in the highest rated part?there was the?physical room for.

From reading some of the data sheets, it looks like the thermistors have a resistance around 3k to 4k when they are hot.

Perhaps one of the members will be able to add onto this story about thermistor characteristics.

Your local suppliers should be able to help you once you figure out what you want.

tom jobe...

?

Show quoted text

----- Original Message -----

From: electric_quattro

To: TekScopes@...

Sent: Tuesday, January 29, 2013 2:31 PM

Subject: [TekScopes] Tek 2235 power issue - A6RT901

?

Hi everyone,

I have just acquired this scope which was sold as not powering on. Once opened up I spotted that RT901 which sits on board A6 had a hole in it. I also measured it at 15ohms out of circuit.

According to the service manual this is a 100ohm thermal resistor, 10%, NTC. However, I am having problems finding a replacement in the UK. Is this part known under a different name?

I've taken a photo which I will add to the site.

Any help greatly appreciated.

Thanks

Alex

#86767

RT901 is 10 Ohm, measures 10-15 ohm out of circuit. Shouldn't really have a hole in it tho' JC

Show quoted text

--- In TekScopes@..., "electric_quattro"  wrote:

Hi everyone,

I have just acquired this scope which was sold as not powering on. Once opened up I spotted that RT901 which sits on board A6 had a hole in it. I also measured it at 15ohms out of circuit.

According to the service manual this is a 100ohm thermal resistor, 10%, NTC. However, I am having problems finding a replacement in the UK. Is this part known under a different name?

I've taken a photo which I will add to the site.

Any help greatly appreciated.

Thanks

Alex

#86770

开云体育

This is a NTC surge resistor. It has a negative temperature coefficient, i.e. it is 10 ohms at 25 °C and drops as its temperature rises. This allows the capacitors to charge up when power is first turned on. It prevents the fuse from blowing. You are most likely reading 15 ohms because the ambient is less than 25 C.

?

Tom

?

Show quoted text

----- Original Message -----

From: Tom Jobe

To: TekScopes@...

Sent: Tuesday, January 29, 2013 7:39 PM

Subject: Re: [TekScopes] Tek 2235 power issue - A6RT901

?

Hi Alex,

I have a good 2235 A6 board that has been removed from a scope, and RT901 measures 15 Ohms in circuit.

The component has no other markings (of use) other than "10 Ohm" (where Ohm is the Ohm symbol).

The A6 schematic shows it as a "10 ohm" part as well.

A?look around the Mouser web site suggests that it might be called an "NTC?thermistor".

Look at this link:

There are links to the datasheets for most of the thermistors, and I would guess that you could figure out the amperage backwards from the physical size of the?RT901 you have.

There is about 20 mm of vertical room under the plastic cover for the thermistor, but?there is room to lay?it over a bit to get some extra space.

I?would consider putting in the highest rated part?there was the?physical room for.

From reading some of the data sheets, it looks like the thermistors have a resistance around 3k to 4k when they are hot.

Perhaps one of the members will be able to add onto this story about thermistor characteristics.

Your local suppliers should be able to help you once you figure out what you want.

tom jobe...

?

?

?

----- Original Message -----

From: electric_quattro

To: TekScopes@...

Sent: Tuesday, January 29, 2013 2:31 PM

Subject: [TekScopes] Tek 2235 power issue - A6RT901

?

Hi everyone,

I have just acquired this scope which was sold as not powering on. Once opened up I spotted that RT901 which sits on board A6 had a hole in it. I also measured it at 15ohms out of circuit.

According to the service manual this is a 100ohm thermal resistor, 10%, NTC. However, I am having problems finding a replacement in the UK. Is this part known under a different name?

I've taken a photo which I will add to the site.

Any help greatly appreciated.

Thanks

Alex

#86795

Thank you all for providing those details so quickly. I will go home and double check the dimensions. I have added the pic to the photos section which highlights the defect.

The two Rifa 2200pF film caps were also badly cracked, but unfortunately my ESR70 meter does not measure at this rating. I have some replacement WIMA FKP1's to put in there.

My next step is to deal with the above and then check the 1amp rectifiers, unless there is anything else which is known cause for power issues on a 2235?

Thanks once again.

Show quoted text

--- In TekScopes@..., "Tom Miller"  wrote:

This is a NTC surge resistor. It has a negative temperature coefficient, i.e. it is 10 ohms at 25 °C and drops as its temperature rises. This allows the capacitors to charge up when power is first turned on. It prevents the fuse from blowing. You are most likely reading 15 ohms because the ambient is less than 25 C.

Tom

  ----- Original Message -----
  From: Tom Jobe
  To: TekScopes@...
  Sent: Tuesday, January 29, 2013 7:39 PM
  Subject: Re: [TekScopes] Tek 2235 power issue - A6RT901

  Hi Alex,
  I have a good 2235 A6 board that has been removed from a scope, and RT901 measures 15 Ohms in circuit.
  The component has no other markings (of use) other than "10 Ohm" (where Ohm is the Ohm symbol).
  The A6 schematic shows it as a "10 ohm" part as well.
  A look around the Mouser web site suggests that it might be called an "NTC thermistor".
  Look at this link:

  There are links to the datasheets for most of the thermistors, and I would guess that you could figure out the amperage backwards from the physical size of the RT901 you have.
  There is about 20 mm of vertical room under the plastic cover for the thermistor, but there is room to lay it over a bit to get some extra space.
  I would consider putting in the highest rated part there was the physical room for.
  From reading some of the data sheets, it looks like the thermistors have a resistance around 3k to 4k when they are hot.
  Perhaps one of the members will be able to add onto this story about thermistor characteristics.
  Your local suppliers should be able to help you once you figure out what you want.
  tom jobe...

    ----- Original Message -----
    From: electric_quattro
    To: TekScopes@...
    Sent: Tuesday, January 29, 2013 2:31 PM
    Subject: [TekScopes] Tek 2235 power issue - A6RT901

    Hi everyone,

    I have just acquired this scope which was sold as not powering on. Once opened up I spotted that RT901 which sits on board A6 had a hole in it. I also measured it at 15ohms out of circuit.

    According to the service manual this is a 100ohm thermal resistor, 10%, NTC. However, I am having problems finding a replacement in the UK. Is this part known under a different name?

    I've taken a photo which I will add to the site.

    Any help greatly appreciated.

    Thanks

    Alex