Date   

3.2 uH wound on 10 ohm resistor (7A26)

TomC
 

A shorted tantalum (C1028) in a 7A26 took out LR1024, a 3.2 uH coil wound on a 10 ohm resistor (LR1024). LR1024 let out a heck of a lot of smoke before I could turn the scope off.

Finding and replacing C1028 was easy. But what to do about LR1024? Just get a 3.2 uH coil and parallel with a 10 ohm resistor? Or get some very fine wire and try to wind my own on a 10 ohm resistor?

It's filtering the 15 volt line, so it probably isn't all that critical.


Tom


Re: 7L5 vanishing trace intensity

Craig Sawyers <c.sawyers@...>
 

I just got a nice looking 7L5 (thank you Dennis!), and tried it out in my trusty R7704 scope,
which is my
go-to frame for plug in testing. here's what happened.
The 7L5 is a power-hungry beast and its introduction postdates the original 7704 by some margin (7
years). Is it possible that it is causing the R7704 rails to lose grip in some way?

Craig


Re: 7L5 vanishing trace intensity

Artek Manuals <manuals@...>
 

Walter


And if you power cycle the scope it comes back ? ...or... you have to
wait for it to cool and then comes back? ...or...it never comes back?


Dave

manuals@...


On 3/31/2017 12:11 PM, @walter2 [TekScopes] wrote:

I just got a nice looking 7L5 (thank you Dennis!), and tried it out in
my trusty R7704 scope, which is my go-to frame for plug in testing.
here's what happened.

I tried the 7L5 in my R7704 (middle slots). It worked great for about
2 minutes, then the SA trace slowly got DIMMER. I kept turning up the
A intensity, but soon ran out of range. Meanwhile, all other screen
info is correct, no shift in intensity. sadly for me, no panel control
on the 7L5 affects this. I am not certain what is occurring, I THINK
it is less frequent digital updates to the screen (the 7L5 has digital
storage) which the eye sees as fainter traces. putting regular plug
ins back in restores perfect operation. It might all be some odd
z-axis interference, but all other traces and data displays remain
unchanged while the 7L5 is fading away. I confess this cause is s
total mystery to me, I could really use some insight into this problem.

all help appreciated,
all the best,
walter (walter2 -at- sphere.bc.ca)

sphere research corp.


[Non-text portions of this message have been removed]

--
Dave
Manuals@...
www.ArtekManuals.com


7L5 vanishing trace intensity

 

I just got a nice looking 7L5 (thank you Dennis!), and tried it out in my trusty R7704 scope, which is my go-to frame for plug in testing. here's what happened.

I tried the 7L5 in my R7704 (middle slots). It worked great for about 2 minutes, then the SA trace slowly got DIMMER. I kept turning up the A intensity, but soon ran out of range. Meanwhile, all other screen info is correct, no shift in intensity. sadly for me, no panel control on the 7L5 affects this. I am not certain what is occurring, I THINK it is less frequent digital updates to the screen (the 7L5 has digital storage) which the eye sees as fainter traces. putting regular plug ins back in restores perfect operation. It might all be some odd z-axis interference, but all other traces and data displays remain unchanged while the 7L5 is fading away. I confess this cause is s total mystery to me, I could really use some insight into this problem.

all help appreciated,
all the best,
walter (walter2 -at- sphere.bc.ca)

sphere research corp.


Re: 2465B repair, missing SMD version A5 board...

satbeginner
 


Re: 2465B repair, missing SMD version A5 board...

satbeginner
 

Update:

with the A5 board from my other scope the basics seem to work.
There is "CT TEST 81 FAIL 03" message, but that could be either calibration or the fact my A5 does not know the 06/09 option board.


At least I know I have to start looking for a 2465B A5 board.


I would not mind if it is broken, I have the time to fix it...
Maybe someone wants to swap a broken A5 for the option board??


Un saludo,


Satbeginner (Leo)


2465B repair, missing SMD version A5 board...

satbeginner
 

Hi all,


yesterday I received my (second..) 2465B I wanted to repair, I bought through eBay from an Italian seller.
I bought it broken, not working, for parts, and although I specifically asked if there were any boards/parts removed from the scope, I received it with the A5 board removed....
It does have an Option 06 or 09 board in it, I have to look better to see what option this is.


I will file a complaint with eBay, but based on previous exercises with eBay I do not expect anything from that.


Anyway, I still wanted to see how much does function on this machine, so I powered it up and checked the Power Supply voltages.
The 10V was a fraction low, like 9,89V, so was the rest, but when I adjusted the 10V all the rest was within spec as well.


So today I will (temporarily) move the A5 board from my first 2465B to this one, to see what will happen.


Meanwhile, if there is anyone out there with a SMD A5 board they gave up on, please let me know.


I will update later.


Un saludo,


Satbeginner (Leo)


Re: Tiny 1/2" Tek Meters available from Walter Shawlee

Brian Clarke <brianclarke01@...>
 

Hello Dennis,



I could be interested in 2 or 4 of these meters. But first, a couple of Qs:

What is their FSD current?

What might shipping to Australia cost?



73 de Brian, VK2GCE.



On Friday, 31 March 2017 12:25 PM, you said:



Walter Shawlee gave me some of his tiny ½” Tek meters and I have a few left
over.

If you are interested in them please let me know off list and I will make
arrangements to ship them to you.

Dennis Tillman W7PF


Tiny 1/2" Tek Meters available from Walter Shawlee

 

Walter Shawlee gave me some of his tiny ½” Tek meters and I have a few left
over.

If you are interested in them please let me know off list and I will make
arrangements to ship them to you.



Dennis Tillman W7PF



From: walter shawlee 2 [mailto:@walter2]
Sent: Friday, March 24, 2017 8:38 AM
To: Holger Lübben <luebben@... <mailto:luebben@...> >; susan shawlee
<susan@... <mailto:susan@...> >; Dennis Tillman
<@Dennis_Tillman_W7pF <mailto:@Dennis_Tillman_W7pF> >
Subject: Re: [TekScopes] Tiny 1/2" Tek Meters avaiiable +_ more



holger,

I will do that, he has a bag of them to take back with him!

all the best,
walter

Walter Shawlee 2, President
Sphere Research Corporation
3394 Sunnyside Rd., West Kelowna, BC
V1Z 2V4 CANADA Phone: (250) 769-1834
@walter2 <mailto:@walter2>
WS2: We're all in one boat, no matter how it looks to you.
Love is all you need. (John Lennon)
But, that doesn't mean other things don't come in handy. (WS2)

On 2017-03-23 11:39 PM, Holger Lübben wrote:

Hi Walter!

At first: Thank you very much for giving me an indicator - they are hard to
find here in Germany!

Please give the indicator to Dennis. He also picks up the indicator(s) for
Rens from the Netherlands.

As far as I know dennis is collecting a bunch of parts and sends them in one
package to Rens.

So I can split the cost with Rens.

Holger





Am 23.03.2017 um 22:13 schrieb walter shawlee 2:

holger,

easily done, but shipping to you is not so cheap, even though the part is
free.
it's possible I could pad it and ship in a padded bag, but it may be too
thick, that is cheapest at $6.
as a small box, it costs $22.

regards,
walter




Walter Shawlee 2, President
Sphere Research Corporation
3394 Sunnyside Rd., West Kelowna, BC
V1Z 2V4 CANADA Phone: (250) 769-1834
@walter2 <mailto:@walter2>
WS2: We're all in one boat, no matter how it looks to you.
Love is all you need. (John Lennon)
But, that doesn't mean other things don't come in handy. (WS2)

On 2017-03-23 01:51 PM, Holger Lübben wrote:

Hi Walter!

What a great find - It would be nice if I could get one of the indicators.

Holger





Am 23.03.2017 um 18:59 schrieb @walter2
<mailto:@walter2> [TekScopes]:



Doing more clean up for Stuff Day, and I found a new bag of the tiny round
RED/GREEN indicating meters that Tek used on things like battery packs for
condition monitoring. I have about twenty of them. if anybody needs some,
contact me off list, plus Dennis will be up this weekend, he possibly can be
persuaded to bring some back for you to avoid shipping. These are FREE if
you can use them, but shipping is up to you.

Lots of 2/3 series plug-ins as well if any interest (fit the 561/564
series), and some 5K plug-ins that need work, any item for just $5.


We also have new mint TM500 storage compartments, and 11K blanking plug ins
available. plus, I am still trying to find Tek 2335/2336 beige case latches
to secure the lids on these portable scopes. anybody out there with some
working ones?



all the best,
walter (walter2 -at- sphere.bc.ca
sphere research corp.


[Non-text portions of this message have been removed]













[Non-text portions of this message have been removed]


Re: [funwithtransistors] OT: Cheap lab equipment recommendations

 

Here are two examples of LCR tweezer probes but there are others which
I did not keep links for:

http://www.lcrresearch.com/
http://www.smarttweezers.com/products-all/

But I think a better way to go is a DE-5000 with the tweezers
attachment:

https://www.amazon.com/-5000-Handheld-LCR-Meter-accessories/dp/B00S298KJO

EEVBlog has discussions about all of these.

On Wed, 29 Mar 2017 23:40:28 +0000, you wrote:

Hi David,
Yeah, a decent tweezer probe for a dmm would be plenty good. Not even
necessarily kelvin, but that would a bonus. Haven't found anything that
wouldn't cost an arm and a leg.


Re: Tektronix 176 tear down, service manual?

Miguel Work
 

Hi

Found it

http://w140.com/tek_176_ocr.pdf

Regards

Miguel

De: TekScopes@...<mailto:TekScopes@...> [mailto:TekScopes@...]
Enviado el: martes, 27 de septiembre de 2016 0:47
Para: TekScopes@...<mailto:TekScopes@...>
Asunto: RE: [TekScopes] Tektronix 176 tear down, service manual?



Hi Miguel,

It appears this may be hard to find. The closest I came was an
Operator/Service manual for sale at
http://vintagemanuals.com/manual/Tektronix/176

There is an operator manual at
http://exodus.poly.edu/~kurt/manuals/manuals/Tektronix/TEK%20176%20Operation
.pdf
and also at
https://doc.xdevs.com/doc/Tektronix/TEK%20176%20Operation.pdf

Dennis Tillman W7PF

-----Original Message-----
Sent: Monday, September 26, 2016 12:27 PM
Subject: [TekScopes] Tektronix 176 tear down, service manual?

Hi, my 176 is working, but I would to know how it works, anyone knows where
I can find a service manual copy?
Some pics:
http://imageshack.com/a/img922/276/9tBHCO.jpg
http://imageshack.com/a/img924/3136/t3WTRN.jpg
http://imageshack.com/a/img923/7923/3m1GGB.jpg
http://imageshack.com/a/img924/2036/96NKJ5.jpg
http://imageshack.com/a/img921/2060/6XWrbZ.jpg
http://imageshack.com/a/img921/6290/oNlKSc.jpg
http://imageshack.com/a/img924/1254/i0bz6Z.jpg
http://imageshack.com/a/img922/2330/w47Eej.jpg
http://imageshack.com/a/img923/8545/fTZryp.jpg
http://imageshack.com/a/img923/5821/P5u6FZ.jpg

Best regards
Miguel
------------------------------------
Posted by: Miguel Work <harrimansat@...<mailto:harrimansat@...>>
------------------------------------


Re: [funwithtransistors] OT: Cheap lab equipment recommendations

 

Hi David,
Yeah, a decent tweezer probe for a dmm would be plenty good. Not even
necessarily kelvin, but that would a bonus. Haven't found anything that
wouldn't cost an arm and a leg.

On Thu, 30 Mar 2017 01:31 David @DWH [TekScopes], <
TekScopes@...> wrote:

On Wed, 29 Mar 2017 04:10:28 +0200, you wrote:

Hi guys,
I have seen some really interesting cheap lab equipment recommended
recently and I thought I would ask: what are some cheap buys you'd
recommend? Many will say "nothing" but for a hobbyist something like a
waveform generator doesn't have to be ultra precise. Same with a power
supply.
Where you thinking of new or relatively new equipment or are older
instruments which are likely to require maintenance acceptable also?

Below are a few of my recommendations with prices and links. But first
some things which I'm still on the lookout for:

- good dual power supplies, up to +/- 15V, 50W, with current limiting,
and able to bring up both rails with one knob. Low noise would be
good. New is good. Should run off mains.
I like the Tektronix PS503A for this. The outputs can be adjusted
individually or track with an adjustable ratio. They are also
floating.

- good low voltage power supplies, well regulated, between 0.5V and
5V, for powering high speed digital circuits, microcontrollers, SoCs,
mobile phones, etc. Could run off mains or 5V.
Tektronix makes the PS505 as a companion to the PS503A although it
only operates from 3 to 5.5 volts. Its output is floating if used in
a high power compartment.

- an inexpensive impedance bridge that can create an impedance plot
from 20 Hz to 100 kHz in small steps. Possibly based off an audio
interface as signal generator and data acquisition?
Some low frequency network analyzers can do this and I think I have
seen units intended for RLC measurements.

- an inexpensive small-signal transistor curve tracer that hooks up to
a PC for data acquisition.
I think this market was taken over by Keithley with their expensive
source/measurement units. Existing transistor checkers do not measure
the characteristics that I would be interested in. Maybe there is a
market here but if so, I would have expected it to have been filled.

- a good, inexpensive pair of smd tweezer probes that isn't utter crap
- your pick! Tell me what I'm missing.
Did you mean for an RLC meter?

The DE-5000 RLC meter supports 4-wire kelvin measurements with a
plug-in tweezer probe and I think it would be better than dedicated
RLC tweezers.


------------------------------------
Posted by: David <@DWH>
------------------------------------


------------------------------------

Yahoo Groups Links




Re: [funwithtransistors] OT: Cheap lab equipment recommendations

 

On Wed, 29 Mar 2017 04:10:28 +0200, you wrote:

Hi guys,
I have seen some really interesting cheap lab equipment recommended
recently and I thought I would ask: what are some cheap buys you'd
recommend? Many will say "nothing" but for a hobbyist something like a
waveform generator doesn't have to be ultra precise. Same with a power
supply.
Where you thinking of new or relatively new equipment or are older
instruments which are likely to require maintenance acceptable also?

Below are a few of my recommendations with prices and links. But first
some things which I'm still on the lookout for:

- good dual power supplies, up to +/- 15V, 50W, with current limiting,
and able to bring up both rails with one knob. Low noise would be
good. New is good. Should run off mains.
I like the Tektronix PS503A for this. The outputs can be adjusted
individually or track with an adjustable ratio. They are also
floating.

- good low voltage power supplies, well regulated, between 0.5V and
5V, for powering high speed digital circuits, microcontrollers, SoCs,
mobile phones, etc. Could run off mains or 5V.
Tektronix makes the PS505 as a companion to the PS503A although it
only operates from 3 to 5.5 volts. Its output is floating if used in
a high power compartment.

- an inexpensive impedance bridge that can create an impedance plot
from 20 Hz to 100 kHz in small steps. Possibly based off an audio
interface as signal generator and data acquisition?
Some low frequency network analyzers can do this and I think I have
seen units intended for RLC measurements.

- an inexpensive small-signal transistor curve tracer that hooks up to
a PC for data acquisition.
I think this market was taken over by Keithley with their expensive
source/measurement units. Existing transistor checkers do not measure
the characteristics that I would be interested in. Maybe there is a
market here but if so, I would have expected it to have been filled.

- a good, inexpensive pair of smd tweezer probes that isn't utter crap
- your pick! Tell me what I'm missing.
Did you mean for an RLC meter?

The DE-5000 RLC meter supports 4-wire kelvin measurements with a
plug-in tweezer probe and I think it would be better than dedicated
RLC tweezers.


Re: Bad 466 fan motor and 465 with no trace.

Dave Voorhis
 

On 29 Mar 2017, at 21:58, David Berlind david@... [TekScopes] <TekScopes@...> wrote:

thanks Bert. Does that mean a fix to the supply corrected the op amp output?

On Wed, Mar 29, 2017 at 1:17 PM, Bert Haskins bhaskins@... <mailto:bhaskins@...>
I guess my other reply got lost.
Before you replace the op-amp, measure the power supply voltages.
On mine, one supply was way off and the op-amp output was wrong.
After replacement things were back the way they should be.
If the 465 power supply is like the 475, some power supply rails use op-amp chips as part of the voltage regulator circuit. On mine, the +15v (as I recall) rail was dead when I got it, caused by the failed op-amp chip.


Re: Bad 466 fan motor and 465 with no trace.

David Berlind
 

thanks Bert. Does that mean a fix to the supply corrected the op amp output?

On Wed, Mar 29, 2017 at 1:17 PM, Bert Haskins bhaskins@...
[TekScopes] <TekScopes@...> wrote:





On 3/29/2017 10:18 AM, David Berlind david@... [TekScopes] wrote:

yes @davidw, that's what I'm hoping to do now:

1. lube the fan motors in both the 465 and 466
2. replace the op-amp in the 465 in hopes of restoring the trace (or,
apply
I guess my other reply got lost.
Before you replace the op-amp, measure the power supply voltages.
On mine, one supply was way off and the op-amp output was wrong.
After replacement things were back the way they should be.

- Bert

other feedback found here)

thank you very much!

On Tue, Mar 28, 2017 at 6:04 PM, David @DWH [TekScopes]
<
TekScopes@...> wrote:



Why not both? :)

Pull or access the 466 fan motor to lubricate the bearings and adjust
the rear fan bearing to see if that is sufficient to fix it. Then
repair the 465.

On Tue, 28 Mar 2017 14:37:33 -0700, you wrote:

I'm trying to determine for my 466 with an ailing fan motor, if it's
better/eaiser to transplant the fan out a 465 that has no trace, or
to fix
the 465's trace problem. :)
[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]


Re: Bad 466 fan motor and 465 with no trace.

Bert Haskins
 

On 3/29/2017 10:18 AM, David Berlind david@... [TekScopes] wrote:

yes @davidw, that's what I'm hoping to do now:

1. lube the fan motors in both the 465 and 466
2. replace the op-amp in the 465 in hopes of restoring the trace (or,
apply
I guess my other reply got lost.
Before you replace the op-amp, measure the power supply voltages.
On mine, one supply was way off and the op-amp output was wrong.
After replacement things were back the way they should be.

- Bert

other feedback found here)

thank you very much!

On Tue, Mar 28, 2017 at 6:04 PM, David @DWH [TekScopes] <
TekScopes@...> wrote:



Why not both? :)

Pull or access the 466 fan motor to lubricate the bearings and adjust
the rear fan bearing to see if that is sufficient to fix it. Then
repair the 465.

On Tue, 28 Mar 2017 14:37:33 -0700, you wrote:

I'm trying to determine for my 466 with an ailing fan motor, if it's
better/eaiser to transplant the fan out a 465 that has no trace, or
to fix
the 465's trace problem. :)
[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]


Re: A Vacuum Tube Curve Tracer for all Tek Semiconductor Curve Trace

 

Hi Cheater,
The original version is in the TekScopes archive.

The latest version of the paper (I have made a few parts changes to improve performance) is always on John Miles web site. The link is
http://www.ke5fx.com/A_VTCT_Adapter_for_All_Tektronix_SCTs_W7PF.pdf

Dennis Tillman W7PF

-----Original Message-----
Sent: Tuesday, March 28, 2017 7:05 PM
Subject: Re: [TekScopes] Re: A Vacuum Tube Curve Tracer for all Tek Semiconductor Curve Trace

Yeah, it would be on page 24, except I don't have the paper any more.
Mind sending out a link again? Thanks.

On Wed, Mar 29, 2017 at 3:27 AM, 'Dennis Tillman' @Dennis_Tillman_W7pF [TekScopes] <TekScopes@...> wrote:
Hi Cheater,
You must have read right past the 2nd sentence that says:
"If you take a look at page 24 of my paper you can see what the first crude fixture looks like"
Dennis Tillman W7PF

-----Original Message-----
Sent: Tuesday, March 28, 2017 2:35 PM
Subject: Re: [TekScopes] Re: A Vacuum Tube Curve Tracer for all Tek
Semiconductor Curve Trace

Hi Dennis,
difficult to picture, mind linking to the article again? Thanks

On Tue, Mar 28, 2017 at 9:45 PM, 'Dennis Tillman' @Dennis_Tillman_W7pF [TekScopes] <TekScopes@...> wrote:
Hi Cheater,
The Vacuum Tube Curve Tracer I came up with can match tubes very simply. This is an important capability that is lacking in the 570 Curve Tracer. If you take a look at page 24 of my paper you can see what the first crude fixture looks like that I made and the pairs of curves it can display. For that one I had to make a plug by hand as several people have suggested but that took several hours and it doesn't look very professional.

All you need is two sockets, a 3 pole double throw switch to switch the grid, screen, and plate voltages, and a plug that you insert into the right socket of the tube tester. To match 7-pin tubes you need a 7-pin plug, ditto for 8-pin octal tubes, and for 9-pin miniature tubes. All I need is a corresponding plug to do this for the tubes that use that socket. That is why I started looking for these plugs. 9-pin and 8-pin plugs are available everywhere. The only 7-pin plugs I have found are on obsolete products.

One possible solution are the Vector pins so I ordered a bag of those. I am hoping they will be sturdy enough to withstand many insertions and removals from the tube tester's sockets. I should be able to make a printed circuit board that they can be swaged into then soldered in place. My hope is that this will be a professional looking solution. They make PC Board mountable sockets which I would also use for this.

Dennis Tillman W7PF

-----Original Message-----
Sent: Tuesday, March 28, 2017 9:56 AM
Subject: Re: [TekScopes] Re: A Vacuum Tube Curve Tracer for all Tek
Semiconductor Curve Trace

So Dennis, why do you need a 7 pin base anyways? I think after 50
messages it's worth asking :^)

On Tue, Mar 28, 2017 at 6:49 PM, David Wise david_wise@... [TekScopes] <TekScopes@...> wrote:
Mouser has three packs of 100 pins each in stock, $12.45 a pack.

Dave Wise
________________________________________
From: TekScopes@... <TekScopes@...> on
behalf of 'Dennis Tillman' @Dennis_Tillman_W7pF [TekScopes]
Sent: Monday, March 27, 2017 9:08 AM
Subject: RE: [TekScopes] Re: A Vacuum Tube Curve Tracer for all Tek
Semiconductor Curve Trace

Hi Bruce,
Vector still makes pins of the right diameter and length (Vector
part
number: K24C/C) that I could press into a PC Board and make a plug
that way, but nobody seems to have these pins in stock.
Dennis Tillman W7PF

-----Original Message-----
Sent: Monday, March 27, 2017 8:38 AM
Subject: [TekScopes] Re: A Vacuum Tube Curve Tracer for all Tek
Semiconductor Curve Trace

Vector used to sell little extruded round aluminum cans with 7-pin
and 9-pin tube pin bases. The bases attached with side screws.
These were used for constructing special plug-in modules. I don't
know if they are still in the Vector product line.

Bruce, KG6OJI
------------------------------------
Posted by: brucekareen@...
------------------------------------
------------------------------------
Posted by: "Dennis Tillman" <@Dennis_Tillman_W7pF>
------------------------------------
------------------------------------
Posted by: cheater00 cheater00 <cheater00@...>
------------------------------------
------------------------------------
Posted by: "Dennis Tillman" <@Dennis_Tillman_W7pF>
------------------------------------
------------------------------------
Posted by: cheater00 cheater00 <cheater00@...>
------------------------------------
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Posted by: "Dennis Tillman" <@Dennis_Tillman_W7pF>
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Posted by: cheater00 cheater00 <cheater00@...>
------------------------------------


Re: OT: FET matching

mosaicmerc
 

Some updates: It appears the FET SOA is being violated by the avalanche
pulse currents.

The BackEmf can charge a 1KuF cap (I measured the capacitance) to 36V in
40mS. It delivers .65J in 40mS = 16.25W
@ 700Hz that translates into 28 pulses. So 1 pulse = 23.2 mJ of kick
back energy.

The capacitor tops out at 38V. Given the avalanche is happening @ 65V =>
the pulse diode resistance is just a bit less than the ESR of the
capacitor which is around 30mΩ; based on the voltage divider formed by
the two as they are in series.

However, the backemf pulse current induced voltage across the 30mΩ
Capacitor ESR is up to 25V. Which is 833Amps!
The rated max avalanche current is 100A per IRFP3206 spec sheet. So this
may be the problem. Even with balanced load sharing across the 4 FETs in
the array, the max avalanche current per device may be being exceeded.


Having snubbed the avalanche I did some thermal tests. With an RMS of
2A, about 280A normal pulse occurs over 20 to 22uS. With the flywheel
in place the transistors had a 3°C temp increase after 10 min.

Without the flywheel and a 5uS avalanche, there is a 15°C temp increase!
So the flywheel certainly siphons off the heating and improves the
transistor SOA.

The avalanche protection is a bit more complex than a flywheel diode. It
is a flywheel in series with a 30mΩ, 50V , 105°C electrolytic cap which
is discharged thru a 10W G4 lamp (16Ω). The purpose is to allow for
accidental reverse connection of a 12V battery load. The lamp limits the
rev. current (and lights up as well) and the cap allows high flywheel
current (>800A). The lamp glows dimly when absorbing some back emf energy.


[Non-text portions of this message have been removed]


Re: 465B Missing B Sweep

David Berlind
 

*@davidw*

This is a 465 (not a 465B) and all I know from the seller of the 465 is
that it has "no trace." I'm unsure if that really means "missing B sweep."

But I am hoping to get my hands on it and find out. Fingers crossed.

On Tue, Mar 28, 2017 at 5:51 PM, David @DWH [TekScopes] <
TekScopes@...> wrote:



Just to verify, you have a 465B with a missing B sweep? Are there any
other symptoms?

1. Check the low voltage power supply outputs just to be sure.

2. Are you operating the B sweep correctly? Make sure it is set to
"runs after" instead of "triggers after".

3. Check the voltage at the output of the delay time potentiometer
shown at the lower left corner of schematic 7. If it was stuck at +15
volts, then I do not think the B sweep would ever be activated.

4. We have had a couple of 465 era oscilloscopes now with bad JFETs in
the sweep integrators. With the B sweep selected, use a voltmeter to
check the sweep B output at the collector of Q4570 shown on schematic
8 to see what it is doing. Also check the level of the B sweep gate
at the emitter of Q4565. These tests can be done at slow time/div
settings so a voltmeter can be used instead of an oscilloscope for
testing.

These B sweep measurements can be compared to measurements taken of
the A sweep at the collector of Q4598 and emitter of Q4497 when the A
sweep is operating to get an idea of what should be happening.

*@DavidW *Thanks, OK, so if the op amp isn't the first place you'd look,
what would be your gut instinct on a failure to produce a trace?

ps: glad to see this discussion produced another advancement in the
understanding of the 465B! At least something good has become of it!

On Tue, Mar 28, 2017 at 11:52 AM, David @DWH [TekScopes]
<
TekScopes@...> wrote:

It should not be difficult at all although that is an odd symptom if
one of the regulators was not operating correctly. It should have
affected more than the B sweep.

I thought maybe there was an operational amplifier buffering the delay
time control like on some other designs but no such luck; in the 465B
that entire circuit is discrete.

On Tue, 28 Mar 2017 10:58:25 -0700, you wrote:

ooh, so maybe I can swap out the opamp? how difficult is that?

FWIW2 At one time my B lost it's trace and the problem turned out to
be
just a bad opamp in one of the voltage regulator circuits.
Easy fix!

[Non-text portions of this message have been removed]


Re: Bad 466 fan motor and 465 with no trace.

David Berlind
 

yes @davidw, that's what I'm hoping to do now:

1. lube the fan motors in both the 465 and 466
2. replace the op-amp in the 465 in hopes of restoring the trace (or, apply
other feedback found here)

thank you very much!



On Tue, Mar 28, 2017 at 6:04 PM, David @DWH [TekScopes] <
TekScopes@...> wrote:



Why not both? :)

Pull or access the 466 fan motor to lubricate the bearings and adjust
the rear fan bearing to see if that is sufficient to fix it. Then
repair the 465.

On Tue, 28 Mar 2017 14:37:33 -0700, you wrote:

I'm trying to determine for my 466 with an ailing fan motor, if it's
better/eaiser to transplant the fan out a 465 that has no trace, or to fix
the 465's trace problem. :)