New Member intro and needing help


j.stumreiter@...
 

Hello, I'm new to the group. I'm a railroad signalman, though I used to be a Simpson meter technician, and I'm still a ham and electronics tech. My major passion is antique radio restoration.

I recently purchased a 2465 as an upgrade from my old 60 MHz Tek 2210. Unfortunately, it was damaged in shipping due to very poor packing. The intensity pot was broken off, the front panel damaged, the handle broken, and the blue filter popped out and was banged up and gouged pretty bad. They refunded me, but that still leaves me with a scope to repair. I've managed to obtain a replacement intensity pot so far, and another member here is helping me with a broken fan collet. I'm in the process of recapping the PSU (With Nichicon PW caps, of course). It otherwise still works well, and I'd like to fully repair it. I'm hoping someone here has a lead on some of the broken mechanical parts listed below.

The 2 plastic spacers between the 2 PSU boards, that mount to the corner holes. (Tek P/N 129-0912-00, and 129-0976-00)
One of the plastic sockets that retains the A4 board (Tek P/N 343-1012-00)
A good 2465 handle
The unobtanium blue CRT filter
A nice condition front bezel, it anyone has one with the IBM branding above the beam finder button.

Any help is much appreciated. Oh, and hello all!


Roy Thistle
 

On Wed, Jun 29, 2022 at 05:15 AM, <j.stumreiter@...> wrote:


My major passion is antique radio restoration.
Hi J.:
Well... just speaking for myself... I hope you didn't get a 2465 just to fix old radios. ( When I was a kid... I fixed lots of them with an old Simpson VOM, and an IT 12 tracer, and parts from even older radios. [There were still bushel baskets of tubes around then!] An oscilloscope... well... that was something only to dream for... and I'm talking about an old OSK-1, or even a kit build IO-18.)

--
Roy Thistle


Roy Thistle
 

On Wed, Jun 29, 2022 at 05:15 AM, <j.stumreiter@...> wrote:


The unobtanium blue CRT filter
Hi J.
AFAIK if blue polycarbonate is unobtainium... then your're out of luck. (There's nothing special about these blue filters... that I recall.)

--
Roy Thistle


Roy Thistle
 

On Wed, Jun 29, 2022 at 05:15 AM, <j.stumreiter@...> wrote:


A good 2465 handle
Hi J.:
I've had 2465 without the case... how that went missing I don't know... and without the handle. Not sure why (vandalistic tendencies?)... but people take the handles of (even rip them off!) and throw them in a drawer. But, try and find the handle again!
The only way I could get a handle (or a case) was to buy a junker, or a parts mule.

--
Roy Thistle


Joel B Walker
 

There seems to be quite a few ARF members here. Welcome!


 

Yup. Me too Joel.

On Wed, Jun 29, 2022, 10:15 PM Joel B Walker <joelandjoyce@...> wrote:

There seems to be quite a few ARF members here. Welcome!






KStrauss <capnslo@...>
 

Greetings everyone-

I have a 7704A that I acquired years and years ago and (sadly) stored in
the garage. And for at least 10 years never used or powered on.

I have now established a repair shop in my office. The Main AC fuse (4A)
blows immediately upon application of power.

I suspect a power supply problem, but could use assistance on:
a - how to get the PS out of the chassis and
b- look for obvious signs of trauma - e.g. leaky capacitor, discolored
resistor, etc etc

Or - rather thnt dig in the issue, would there be a functional replacement
on the market?

Thank you

Karl Strauss
Santa Clarita CA


n4buq
 

Hi Karl,

The power supply is held in with four (Pozidriv) screws from the back side. Removing those allows the entire LVPS to be slid out the back. There are two coaxial wires (pay attention to which color goes where but it's outlined in the manual) and two multi-connector plugs where the output and sense wires connect.

It is a switch-mode power supply (SMPS) and will need a sufficient load to work properly or it will go into "tick mode". One of our members, Dennis Tillerman(sp?), created a document showing how to build one of those. It's pretty simple and I built a similar one when I was troubleshooting my 7704A's power supply.

Hopefully you have a manual. It's invaluable for this sort of thing.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "KStrauss" <capnslo@...>
To: "tekscopes" <TekScopes@groups.io>
Sent: Thursday, June 30, 2022 10:57:40 AM
Subject: Re: [TekScopes] New Member intro and needing help
Greetings everyone-

I have a 7704A that I acquired years and years ago and (sadly) stored in
the garage. And for at least 10 years never used or powered on.

I have now established a repair shop in my office. The Main AC fuse (4A)
blows immediately upon application of power.

I suspect a power supply problem, but could use assistance on:
a - how to get the PS out of the chassis and
b- look for obvious signs of trauma - e.g. leaky capacitor, discolored
resistor, etc etc

Or - rather thnt dig in the issue, would there be a functional replacement
on the market?

Thank you

Karl Strauss
Santa Clarita CA



SCMenasian
 

Getting the power supply out is a cinch. It is held in by 4 screws on the back and you can slide it out with the cables still connected.

The manual has a procedure for finding faults. IIRC, you measure various resistances and see how they change as you disconnect cables on the interface board. The power supply, itself, has only 2 cables - one for power and one for load point sensing.

Mine did not blow fuses. Yours might have a switcher problem, or a shorted rectifier or capacitor.

In my case, the fault Itick mode) was a capacitor on the interface board. Removal of this board involves careful disassembly with lots of notes (which cable goes where, etc.) .


stevenhorii
 

Barry mentions that the screws are Pozidriv for a reason. They look like
Phillips but are not. Using Phillips screwdrivers for them can damage the
heads especially if they are tight. That can make future removal or
tightening difficult. I bought a used H-P counter and had to drill out one
of the Pozidriv screws because it was so damaged. It is worth buying a set
of Pozidriv drivers or bits if you work on Tek or H-P equipment.

On Thu, Jun 30, 2022, 13:23 n4buq <n4buq@...> wrote:

Hi Karl,

The power supply is held in with four (Pozidriv) screws from the back
side. Removing those allows the entire LVPS to be slid out the back.
There are two coaxial wires (pay attention to which color goes where but
it's outlined in the manual) and two multi-connector plugs where the output
and sense wires connect.

It is a switch-mode power supply (SMPS) and will need a sufficient load to
work properly or it will go into "tick mode". One of our members, Dennis
Tillerman(sp?), created a document showing how to build one of those. It's
pretty simple and I built a similar one when I was troubleshooting my
7704A's power supply.

Hopefully you have a manual. It's invaluable for this sort of thing.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "KStrauss" <capnslo@...>
To: "tekscopes" <TekScopes@groups.io>
Sent: Thursday, June 30, 2022 10:57:40 AM
Subject: Re: [TekScopes] New Member intro and needing help
Greetings everyone-

I have a 7704A that I acquired years and years ago and (sadly) stored in
the garage. And for at least 10 years never used or powered on.

I have now established a repair shop in my office. The Main AC fuse (4A)
blows immediately upon application of power.

I suspect a power supply problem, but could use assistance on:
a - how to get the PS out of the chassis and
b- look for obvious signs of trauma - e.g. leaky capacitor, discolored
resistor, etc etc

Or - rather thnt dig in the issue, would there be a functional
replacement
on the market?

Thank you

Karl Strauss
Santa Clarita CA







Roy Thistle
 

On Thu, Jun 30, 2022 at 10:42 AM, stevenhorii wrote:


I bought a used H-P counter and had to drill out one
of the Pozidriv screws because it was so damaged.
Hi All:
IMO, it's worth mentioning that one is more likely to damage a Phillips screw, with a Pozidriv bit, than the other way around.
I'm not saying to use a Phillips bit, in a Pozidriv screw... just saying... I do it all the time; but, 'feel' for cam out, and watch for damage.
I have seen, more than a few, damaged screw heads on older HP test gear.
Besides the damage possibly occurring through using the incorrect bit to try to extract the screw... HP seems to have had a fashion of using steel screws in cast aluminum parts... that sometimes gall.

--
Roy Thistle


Roy Thistle
 

On Thu, Jun 30, 2022 at 09:29 AM, KStrauss wrote:


The Main AC fuse (4A) blows immediately upon application of power.
With old gear... out of service for a long time (and perhaps, stored inappropriately) ... IMO...it's asking for it to just plug it in, turn it on, and hope for the best.
IMO, one should never do that. (We've all learned the hard way!)
One can potentially avoid cascading failures, and destroying hard to get (and expensive!) parts by taking the time to go through an appropriate "power up" procedure.


--
Roy Thistle


Roy Thistle
 

On Thu, Jun 30, 2022 at 09:29 AM, KStrauss wrote:


Or - rather thnt dig in the issue, would there be a functional replacement on the market?
As these smps were designed in the most byzantine fashion (necessitated by the semiconductors, and magnetics of the time... as well as circuitry's multi-voltage power requirements)... an off-the-shelf, or "functional replacement" smps turns out to be a 7704A mule.

--
Roy Thistle


John Kolb
 

If it is the 4 Amp Line fuse (F3001) instead the 2 Amp Inverter fuse (F3003) (page 6-17 of service manual), that's good news. There's not much circuitry between the two fuses. A short after that should blow the 2 A FUSE FIRST. In my case, it was the bridge rectifier with a shorted diode. Replaced with a BR610, 1 KV 6A bridge I had handy.Broke my arm and haven't been able to reassemble :)

John

On 6/30/2022 8:57 AM, KStrauss wrote:
Greetings everyone-
I have a 7704A that I acquired years and years ago and (sadly) stored in
the garage. And for at least 10 years never used or powered on.
I have now established a repair shop in my office. The Main AC fuse (4A)
blows immediately upon application of power.
I suspect a power supply problem, but could use assistance on:
a - how to get the PS out of the chassis and
b- look for obvious signs of trauma - e.g. leaky capacitor, discolored
resistor, etc etc
Or - rather thnt dig in the issue, would there be a functional replacement
on the market?
Thank you
Karl Strauss
Santa Clarita CA


j.stumreiter@...
 

No, I got it to do mostly other projects. Antique radios is just my primary hobby. I work with lots of other analog circuits as well.

So I managed to score another blue filter and an Intensity pot. Now it looks like I just need the power supply board spacers, A4 board plastic mounting socket, handle, and front bezel.


druid_noibn
 

Hi Roy,
What would be a good or appropriate power-up procedure for for older 'scopes that sat on the shelf for a few years?

Kind regards,John aka DBN

On Thursday, June 30, 2022 at 03:28:01 PM EDT, Roy Thistle <roy.thistle@...> wrote:

On Thu, Jun 30, 2022 at 09:29 AM, KStrauss wrote:


The Main AC fuse (4A) blows immediately upon application of power.
With old gear... out of service for a long time (and perhaps, stored inappropriately) ... IMO...it's asking for it to just plug it in, turn it on, and hope for the best.
IMO, one should never do that. (We've all learned the hard way!)
One can potentially avoid cascading failures, and destroying hard to get (and expensive!) parts by taking the time to go through an appropriate "power up" procedure.


--
Roy Thistle


Jim Adney
 

On Fri, Jul 1, 2022 at 09:50 AM, druid_noibn wrote:

What would be a good or appropriate power-up procedure for for older 'scopes that sat on the shelf for a few years?
There are two good approaches:

Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltage

or

Build a fixture that puts an incandescent bulb in series with the old device. I built mine using a 2x4 box and a cover that had an outlet and a socket for a screw-in (Edison base) lamp. Choose a bulb that will almost, but not quite, blow the fuse. As long as the lamp doesn't glow brightly, you're okay. If the lamp suddenly goes bright, you know that something in your old device has shorted.

You could also do both, using the Variac to bring the voltage up slowly, while watching the lamp to monitor the current.


 

Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltage
Just don't do this if the 'scope has a switching Power Supply (like most 7000 series and later 'scopes).

Just plug in an turn on (after checking the voltage selector is set correctly).

Dim bulb approach is fine.
D.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Jim Adney
Sent: 02 July 2022 12:48
To: TekScopes@groups.io
Subject: Re: [TekScopes] New Member intro and needing help

On Fri, Jul 1, 2022 at 09:50 AM, druid_noibn wrote:

What would be a good or appropriate power-up procedure for for older 'scopes that sat on the shelf for a few years?
There are two good approaches:

Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltage

or

Build a fixture that puts an incandescent bulb in series with the old device. I built mine using a 2x4 box and a cover that had an outlet and a socket for a screw-in (Edison base) lamp. Choose a bulb that will almost, but not quite, blow the fuse. As long as the lamp doesn't glow brightly, you're okay. If the lamp suddenly goes bright, you know that something in your old device has shorted.

You could also do both, using the Variac to bring the voltage up slowly, while watching the lamp to monitor the current.


Zentronics42@...
 

I agree with this as well Variac turn on for linier power supplies is the way to go. However using a variac on a switches can cause damage to the switching components as they try and force regulate without enough power. They make up for it in current. And can easily over current the switching transistors. A good rule of thumb in the 7xxx frames is 3 bay units are usually linier power supplies 4 bay units are always switchers. There are a few 3 bay units with switching supplies if I remember correctly.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of David C. Partridge
Sent: Saturday, July 2, 2022 11:17 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] New Member intro and needing help

Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltage
Just don't do this if the 'scope has a switching Power Supply (like most 7000 series and later 'scopes).

Just plug in an turn on (after checking the voltage selector is set correctly).

Dim bulb approach is fine.
D.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Jim Adney
Sent: 02 July 2022 12:48
To: TekScopes@groups.io
Subject: Re: [TekScopes] New Member intro and needing help

On Fri, Jul 1, 2022 at 09:50 AM, druid_noibn wrote:

What would be a good or appropriate power-up procedure for for older 'scopes that sat on the shelf for a few years?
There are two good approaches:

Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltage

or

Build a fixture that puts an incandescent bulb in series with the old device. I built mine using a 2x4 box and a cover that had an outlet and a socket for a screw-in (Edison base) lamp. Choose a bulb that will almost, but not quite, blow the fuse. As long as the lamp doesn't glow brightly, you're okay. If the lamp suddenly goes bright, you know that something in your old device has shorted.

You could also do both, using the Variac to bring the voltage up slowly, while watching the lamp to monitor the current.


John Kolb
 

In my younger days, I've turned on a long unused scope, and after a couple of minutes, heard a loud bang as a cap exploded.

The electrolytic cap anode is a metal with a thin insulating oxide layer. After long idle periods, the oxide layer disappears. When voltage is applied without the insulating oxide layer, large current flows, causing heat, pressure, and eventually BANG.

I power up unknown equipment by turning power on for 10 sconds, then off again, Wait awhile so that if heating occurred, the cap can cool off again. Another power on, 15 seconds, this time; another cooldown. The process continues with increasing on time periods until I run out of patience. The applied voltage causes the oxide layer to form again

I don't know if this theory is correct or not, but I haven had any explosions while using it.

John

On 7/2/2022 8:17 AM, David C. Partridge wrote:
Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltage
Just don't do this if the 'scope has a switching Power Supply (like most 7000 series and later 'scopes).
Just plug in an turn on (after checking the voltage selector is set correctly).
Dim bulb approach is fine.
D.