Date   

Re: 7L13 Phase Lock Fault

Attilio
 

Sorry Miguel how do I put the video on youtube, I never did!

Thank you
--Cheers
Attilio


Re: PG506 Repair - I had a Great Day today/

-
 

Since shorted pass transistors in the TM 50xs are so common, I wonder
if it would be a good idea to add either an overload prevention circuit,
i.e. a fuse, or an over voltage detection circuit and output cutoff to to
the extender cards? A simple SCR crowbar circuit with a fuse would be
enough to prevent damage to anything plugged into the extender.

On Tue, Apr 20, 2021 at 9:07 AM Michael W. Lynch via groups.io <mlynch003=
yahoo.com@groups.io> wrote:

On Mon, Apr 19, 2021 at 04:47 PM, Tom Lee wrote:


I’ve never seen such a large collection of blown components in a single
unit. Your persistence paid off!
Tom,
Thanks! I think this is what made the repair so difficult.

For clarification, and after thinking back, I recalled that this was the
plug in where i mistakenly inverted my flexible extender and likely damaged
more than a "normal" complement of parts. I did plug it into the TM506
with a "bad" pass transistor, (the trouble started there) but the bone
headed error of inverting the extender greatly exacerbated the damage.
This was a teaching moment for me, from that point on, I NEVER plug in a
flexible extender without triple checking for correct orientation. This
was also my inspiration for building the TM500 Tester Project.

Bottom line is that what I have learned from this group made it possible
to recover the instrument, in spite of my early "ham fisted" effort to the
contrary.

Sincerely,

--
Michael Lynch
Dardanelle, AR






Re: PG506 Repair - I had a Great Day today/

Michael W. Lynch
 

On Tue, Apr 20, 2021 at 04:56 AM, tek_547 wrote:


René Stay safe and maybe you have any suggestions.
René,

Thanks for your kind response.

Perhaps I can help as this was my problem as well.

Would you be so kind as to tell me what parts you have already changed?

Do you see the "88" when you push the "variable" in?
Does the amplitude of the waveform respond to turning the "variable" knob or remain fixed at one level?
Do the amplitudes generated in each switch position agree with the selected value of the switch across all positions?

I will be glad to try to give some ideas from there.

Sincerely,

--
Michael Lynch
Dardanelle, AR


Re: PG506 Repair - I had a Great Day today/

Michael W. Lynch
 

On Mon, Apr 19, 2021 at 04:47 PM, Tom Lee wrote:


I’ve never seen such a large collection of blown components in a single
unit. Your persistence paid off!
Tom,
Thanks! I think this is what made the repair so difficult.

For clarification, and after thinking back, I recalled that this was the plug in where i mistakenly inverted my flexible extender and likely damaged more than a "normal" complement of parts. I did plug it into the TM506 with a "bad" pass transistor, (the trouble started there) but the bone headed error of inverting the extender greatly exacerbated the damage. This was a teaching moment for me, from that point on, I NEVER plug in a flexible extender without triple checking for correct orientation. This was also my inspiration for building the TM500 Tester Project.

Bottom line is that what I have learned from this group made it possible to recover the instrument, in spite of my early "ham fisted" effort to the contrary.

Sincerely,

--
Michael Lynch
Dardanelle, AR


Re: 7L13 Phase Lock Fault

Miguel Work
 

Can you pleas make a video and share it in youtube, I will compare with mine

-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Attilio
Enviado el: martes, 20 de abril de 2021 14:23
Para: TekScopes@groups.io
Asunto: [TekScopes] 7L13 Phase Lock Fault

Hello everyone
I'm haunted by phase lock failures. When I select span / div at 50 kHz or lower the signal on the screen does not stand still and hops from left to right. I also noticed that the noise (Klank) of switching from 100 kHz span / div to 50 kHz span / div is no longer heard, but only a relay (click).
The rest seem to work fine.
The 7L13 is very compact, if you have targeted advice on where to investigate / act I would be grateful.

-- Cheers
Attilio


7L13 Phase Lock Fault

Attilio
 

Hello everyone
I'm haunted by phase lock failures. When I select span / div at 50 kHz or lower the signal on the screen does not stand still and hops from left to right. I also noticed that the noise (Klank) of switching from 100 kHz span / div to 50 kHz span / div is no longer heard, but only a relay (click).
The rest seem to work fine.
The 7L13 is very compact, if you have targeted advice on where to investigate / act I would be grateful.

-- Cheers
Attilio


Re: PG506 Repair - I had a Great Day today/

tek_547
 

Thanx Michael for your detailed repair summary. My PG506 (also >B40000) functions normal but only has a strange display behaviour; when switched on STD AMPL. (and VAR AMPL. out) and rotating the VAR AMPL. only the HIGH led is continuous lighting and the LOW led never goes on. The (variable) values of the output signal varies normal up and down when rotating the VAR knob
Also the display is not given the actual value of the setting. I changed almost everything but it is difficult to understand and to troubleshoot it, so with your information maybe I got a step further.

René Stay safe and maybe you have any suggestions.


Re: Yet another 7934 power supply debug?

Albert Otten
 

(continued, hit Reply by accident.) As a current limiter use a heavy bulb in series with the mains power. The PS should go to (audible) tick mode because of voltage overload. The bulb should hardly glow, except for the flash when the big caps get charged. Probably the bulb will show full brightness because of a short or other fault in the inverter (primary side).
Albert


Re: Yet another 7934 power supply debug?

 

I've had several bulk capacitors in these PSU's behave fine at low test voltages and break down at higher voltages. I live in 230VAC land.
The main fuse breaking down often points at the bulk caps or a shorted primary rectifier.

Raymond


Re: Yet another 7934 power supply debug?

Albert Otten
 

On Tue, Apr 20, 2021 at 07:40 AM, Dave Peterson wrote:


I feel like I should try applying power with the mainframe's connectors
disconnected. Is this a bad thing to do? Run with no load? I've done a cursory
search here, and saw a thread where Dennis (I think?) was talking about
building dummy loads? Is that necessary for just verifying the supply itself
is or isn't the source of the fuse blowing? Mostly I guess I'm wondering what
harm that might cause. Also clearly fishing for ideas or common problems.
In my opinion dummy loads won't help you in this stage. They are needed when you want to find out what causes the PS to fall in tick mode.


Re: Yet another 7934 power supply debug?

 

Shorted bulk capacitor (those 900uF ones), or rectifier bridge are the 1st suspects if the main fuse blows.

D.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Dave Peterson via groups.io
Sent: 20 April 2021 06:41
To: TekScopes@groups.io
Subject: [TekScopes] Yet another 7934 power supply debug?

Hi All,

I picked up a 7934 this past weekend, and I tried to power it up today. Sadly as soon as the panel lit up, it went out. Checked the main fuse, and sure enough it was out.


Re: OT Chip Quik - which one to choose

 

Thanks to all of you for constructive useable answers!
I have now ordered SMD1 from Mouser

Mouser is my first choice here, because they maintain a very well-stocked warehouse in Israel - with delivery within a couple of days.

After that is Digikey, who ship to Israel and deliver within 2 weeks.

And after that, all the other players.....


Yet another 7934 power supply debug?

Dave Peterson
 

Hi All,

I picked up a 7934 this past weekend, and I tried to power it up today. Sadly as soon as the panel lit up, it went out. Checked the main fuse, and sure enough it was out.

I pulled down the manual from Tek Wiki and started studying. Fortunately there is some really nice debug and and disassembly instructions.

The scope is in good shape, has been stored well for 10ish years, and was locally picked up - not shipped. I've gotten the PS out and covers off. No obvious critters inside, nor obvious damage. Why would the fuse blow now? Obviously it was fine before I pushed the switch. Guess that's kind of a moot question. It did. Deal with it Dave. But what goes that bad sitting in a clean dry shed?

Moving on: I went through the resistance checks described in the Maintenance section, step B, and there are no low resistances. The only anomalous resistance would be the -50v test point that showed about 4k ohm instead of 500 ohm. I also disconnected the ribbon cables to the mainframe and rechecked resistances. The loads are pretty clear on the supplies when connecting and disconnecting the cables while watching the voltage test points. So there don't appear to be any shorts at the back end of the PS nor in the mainframe itself.

I'm a little confused by the manuals debug procedure. It's not really dealing with a blowing fuse. The step C and later steps presume things are working somewhat, but I don't feel like repeatedly blowing fuses trying to test details when I know it's just going to blow the fuse again. No reason it shouldn't.

I've done some of my own cursory checks of input side components. There's no obvious shorts on the line side of the PS. I can test continuity through the first rectifier. The big blue caps are not shorted and hold charge. Test points beyond the first transformer are not shorted to ground nor to the neutral side.

I feel like I should try applying power with the mainframe's connectors disconnected. Is this a bad thing to do? Run with no load? I've done a cursory search here, and saw a thread where Dennis (I think?) was talking about building dummy loads? Is that necessary for just verifying the supply itself is or isn't the source of the fuse blowing? Mostly I guess I'm wondering what harm that might cause. Also clearly fishing for ideas or common problems.

Four amp fuses coming from Amazon tomorrow. Would like to move to "live" testing by isolating blocks and components logically. Any suggestions would be appreciated.

Dave


Re: Free new Tek 152-0383-00 SMTD-898 Tunnel Diode

snapdiode
 

I have been searching for a 152-0230-00, aka CR71 in the 2901 time mark generator. It's some sort of tiny button package. It's a "capacitance diode". Would you happen to have one? Maybe under the couch, or behind the fridge? My 2901 has no 500MHz output, and needless to say the endless taunting from the neighborhood kids is very hurtful.


Re: CRT Tester

greenboxmaven
 

All CRT testers I have ever seen or used are totally devoted to checking for heater-cathode shorts, cathode-grid shorts, and emission. Rejuvination circuits and concepts vary widely, but aside fron heater voltage, I have never seen any sort of settings for a particular tube. I will make a guess that a good scope tube is likely to read lower on emission that a television tube, especially a color tube.

     Bruce Gentry, KA2IVY

On 4/19/21 17:39, wallydoc via groups.io wrote:
I rescued a nice looking B&K CRT tube tester. Model 465
Has the manual and the connectors also.
From TV repair guy.
I do not know if it can test scope tubes or not,so I thought I would ask here first.

Wally KC9INK




Re: CRT Tester

Paul Amaranth
 

Some of the Sencore units will list a few of the common commercial electrostatic
CRTs (think Eico or Heathkit) but none of the Tek/HP/etc tubes.

The units may provide some value in rejuvinating a dim CRT or maybe clearing
a short. In those cases you don't have much to lose anyway. They will
test them in a general way, mostly for emission. The Sencore manual, at
least, gives enough information so you can set it up for nonlisted tubes.

I have a 576 that's double peaking. One of these days I will try my
CR70 on it and see what happens.

Like a lot of test equipment, prices on those things are getting out of
hand. You used to be able to find a CR70 around $75 a couple years back.

Paul

On Mon, Apr 19, 2021 at 06:18:30PM -0700, Tom Lee wrote:
Right--no commercial testers (that I'm aware of) have chart listings for such specialized crts. Pretty much any CRT tester probably has the bits needed to perform at least a basic test, but you'd have to do the extra work of hooking up this to that and then interpreting the readings.

Sent from an iThing, so please forgive the typos and brevity

On Apr 19, 2021, at 17:53, "David Holland" <david.w.holland@gmail.com> wrote:

On Mon, Apr 19, 2021 at 7:15 PM Tom Lee <tomlee@ee.stanford.edu> wrote:

Be advised that the BK will not have a chart listing for any Tek-made CRTs.

Doesn't that apply to all of the generally available commercial testers?
('cause if I'm wrong I wouldn't mind keeping an eye out for something.)

I've heard rumors that the Sencore CR-70 (and 7000?) can test Tek CRTs, but
those two testers tend to go for more than I'm willing to gamble on whim,
and a rumor.
Even then, I'd still be surprised if they included a chart listing for any
of them.

David
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix/Linux - We don't do windows


Re: CRT Tester

shalopt
 

Should, had one years back recall think it just measures emission.
Will obviously need to make adapters, mine had adapters for all
known TV CRTs at the time.
Gary G


Re: CRT Tester

Tom Lee
 

Right--no commercial testers (that I'm aware of) have chart listings for such specialized crts. Pretty much any CRT tester probably has the bits needed to perform at least a basic test, but you'd have to do the extra work of hooking up this to that and then interpreting the readings.

Sent from an iThing, so please forgive the typos and brevity

On Apr 19, 2021, at 17:53, "David Holland" <david.w.holland@gmail.com> wrote:

On Mon, Apr 19, 2021 at 7:15 PM Tom Lee <tomlee@ee.stanford.edu> wrote:

Be advised that the BK will not have a chart listing for any Tek-made CRTs.

Doesn't that apply to all of the generally available commercial testers?
('cause if I'm wrong I wouldn't mind keeping an eye out for something.)

I've heard rumors that the Sencore CR-70 (and 7000?) can test Tek CRTs, but
those two testers tend to go for more than I'm willing to gamble on whim,
and a rumor.
Even then, I'd still be surprised if they included a chart listing for any
of them.

David





Re: CRT Tester

David Holland
 

On Mon, Apr 19, 2021 at 7:15 PM Tom Lee <tomlee@ee.stanford.edu> wrote:

Be advised that the BK will not have a chart listing for any Tek-made CRTs.

Doesn't that apply to all of the generally available commercial testers?
('cause if I'm wrong I wouldn't mind keeping an eye out for something.)

I've heard rumors that the Sencore CR-70 (and 7000?) can test Tek CRTs, but
those two testers tend to go for more than I'm willing to gamble on whim,
and a rumor.
Even then, I'd still be surprised if they included a chart listing for any
of them.

David


Re: CRT Tester

Tom Lee
 

Be advised that the BK will not have a chart listing for any Tek-made CRTs.

Sent from my iThing, so please forgive typos and brevity.

On Apr 19, 2021, at 3:45 PM, Charles Plunk <af4o@twc.com> wrote:

Before I sold my B&K 470, I made an adapter with all grabber leads so if did not have the right adapter. Worked well just a bit time consuming to hook up.

Sometimes I did not have the setup data to properly test but would guess, lol. And the 470 had a rejuvenation function which sometimes would save a CRT.

Chuck
AF4O

On 4/19/21 4:39 PM, wallydoc via groups.io wrote:
I rescued a nice looking B&K CRT tube tester. Model 465
Has the manual and the connectors also.
From TV repair guy.
I do not know if it can test scope tubes or not,so I thought I would ask here first.

Wally KC9INK






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