Date   

Re: Free TWD 120

Thomas Garson
 

Yes, isn't it.

Apparently even Tektronics was not above a well executed kludge.

Thomas Garson
Aural Technology, Ashland, OR
By my calculation, the dynamic range of the universe is roughly 679dB,
which is approximately 225 bits, collected at a rate 1.714287514x10^23 sps.

On 9/22/20 10:52 PM, ykochcal wrote:
Interesting dead bug looking patch in the last picture
John


Re: Shipping Scopes

greenboxmaven
 

Fedex and UPS pack things fairly well, I have not had any damage. It can be pricey, but is usually less then traveling to pick something up. Some people offering equipment demand that you pick it up from them. I have accounts with both Fedex and UPS, that allows me to take care of everything from my end and convince reluctant sellers to take items to the stores. I ask everyone who demands pickup only to reconsider and be willing to take the item to a shipper who will take care of the packing and shipping.

Bruce Gentry, KA2IVY

On 9/23/20 10:31 AM, Eric wrote:
Ups , FedEx. At least in the US. Use heavy card board and at minimum 2
inches of loose padding all round for shock. I have gotten them double
boxes before and a 576 even in a wooden crate the trick is limiting
movement in the box I double boxed a high end computer it made it safely to
California from the east side. But it was not cheap to ship. I have also
been successful crating things and shipping them freight. Plywood and
padding is wonder for protecting the device.

On Wed, Sep 23, 2020, 10:26 AM Adam Beasley <abeasley@outlook.com> wrote:

Is there a good service to use to ship scopes? The only boxes I have
available are from Amazon and they are not very sturdy so I wouldn't trust
shipping something heavy and expensive in them.

Thanks,
Adam








Re: Shipping Scopes

Eric
 

Ups , FedEx. At least in the US. Use heavy card board and at minimum 2
inches of loose padding all round for shock. I have gotten them double
boxes before and a 576 even in a wooden crate the trick is limiting
movement in the box I double boxed a high end computer it made it safely to
California from the east side. But it was not cheap to ship. I have also
been successful crating things and shipping them freight. Plywood and
padding is wonder for protecting the device.

On Wed, Sep 23, 2020, 10:26 AM Adam Beasley <abeasley@outlook.com> wrote:

Is there a good service to use to ship scopes? The only boxes I have
available are from Amazon and they are not very sturdy so I wouldn't trust
shipping something heavy and expensive in them.

Thanks,
Adam






Re: Shipping Scopes

Bill Riches
 

Depending on how many boxes you need check out Uline.  They have double wall boxes of all sizes.  Staples have some boxes that are better than the Amazon boxes.  
73,
Bill, WA2DVUCape May, NJ

On Wednesday, September 23, 2020, 10:26:12 AM EDT, Adam Beasley <abeasley@outlook.com> wrote:

Is there a good service to use to ship scopes?  The only boxes I have available are from Amazon and they are not very sturdy so I wouldn't trust shipping something heavy and expensive in them.

Thanks,
Adam


Shipping Scopes

Adam Beasley
 

Is there a good service to use to ship scopes? The only boxes I have available are from Amazon and they are not very sturdy so I wouldn't trust shipping something heavy and expensive in them.

Thanks,
Adam


Re: Is my Tek 468 beyond repair?

SCMenasian
 

You're right - my fingers were typing faster than my brain.

SCM


Re: Is my Tek 468 beyond repair?

John
 

Replacement 5V crystal arrived today. Extremely fast dispatch but its output is only 1.2Vpp and nowhere near the expected TTL level!

I modeled satbegginers idea in LTSpice but couldn't get it to work properly. The output was barely above zero. Scm's idea works well enough though provided NPN collector goes to Vcc and PNP collector goes to ground! I used 2N2222 for the NPN (transition frequency=250MHz) and 2N2907 for the PNP (transition frequency=200MHz).


Re: 7623A Storage problem

Roger Evans
 

Colin,

I had the afterthought about low voltages since the regulation of the power transistor Q1195 relies on +5V, +15V and +130V being OK. The components I mentioned are all on the low voltage side of the transformer T1199 and can be checked with the power off. Q1195 is attached by a plug and socket so it can effectively be tested out of circuit, Q1190 can be checked as a pair of diodes for open circuit / short circuit. The two capacitors are likely to be short circuit if they have failed and L1198 will be open circuit if the fuse didn't do its job in time.

At least you don't have to wait 30 minutes for the high voltage to leak away!

Regards,

Roger


Re: Tek 7854 intermittent issues

 

On 23. Sep 2020, at 14:57, Chuck Harris <cfharris@erols.com> wrote:
....
My favorite is the bootstrap capacitor, which is
invariably some cheap piece of Chinese garbage
capacitor in a sea of Nichicon's, or other good
quality capacitors.
Chuck,

thats how I would engineer if I wanted planned obsolescence... a nice single point of failure.

cheers
Martin


Re: Tek 7854 intermittent issues

Chuck Harris
 

Honestly, that is what I find in about 80% of the
repairs I do. A single poorly sourced capacitor
wrecked all orderly operation.

My favorite is the bootstrap capacitor, which is
invariably some cheap piece of Chinese garbage
capacitor in a sea of Nichicon's, or other good
quality capacitors.

-Chuck Harris

David C. Partridge wrote:

The ripple on the -5V looked really quite high ...

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Nick Corvid
Sent: 23 September 2020 09:29
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 7854 intermittent issues

Not very good at finding things on schematics but I'm fairly sure that the funky looking capacitor is A27C321 I'll have to look through my stuff and see if I have a spare of a decent value on hand. Also if I'm reading things correctly it has to do with the +5 volt rail, but it seems strange that all these issues would be caused by a single sad cap that's kind of out of the way. So I'll keep looking for what is causing these problems in the meantime before I find a replacement and see if that changes anything at all.











Re: Tek 7854 intermittent issues

 

The ripple on the -5V looked really quite high ...

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Nick Corvid
Sent: 23 September 2020 09:29
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 7854 intermittent issues

Not very good at finding things on schematics but I'm fairly sure that the funky looking capacitor is A27C321 I'll have to look through my stuff and see if I have a spare of a decent value on hand. Also if I'm reading things correctly it has to do with the +5 volt rail, but it seems strange that all these issues would be caused by a single sad cap that's kind of out of the way. So I'll keep looking for what is causing these problems in the meantime before I find a replacement and see if that changes anything at all.


Re: 7623A Storage problem

Colin Herbert
 

Hi Roger,

Thanks for all the ideas. I am a bit careful with voltages over 1 KV, but in the past, when I was still at school, I caught a belt at 2 KV on a homebrew scope that I was trying to build. This was from a mains-transformer supply with a voltage doubler and so was low-impedance and capable of quite a whack. It came about from a leaky capacitor which was supposed to be keeping the X-modulation input safe. More fool me!

With regard to the 7623A, I think I mentioned that I had checked all of the voltages from the low-voltage DC supply and found that they were all in spec. I might also have mentioned that I could see the sweep output on the BNC at the back of the scope, so a good few voltages are obviously ok.

I suppose I should gird my loins and try to gain safe access to the high-voltage board and that heat-sunk transistor Q1195.

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Roger Evans via groups.io
Sent: 23 September 2020 11:13
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7623A Storage problem

Apologies - I skipped the very important 'check all the low voltage DC supplies', there are so many inter-dependencies in these scopes.

Roger


Re: 7623A Storage problem

Roger Evans
 

Apologies - I skipped the very important 'check all the low voltage DC supplies', there are so many inter-dependencies in these scopes.

Roger


Re: 7623A Storage problem

Roger Evans
 

Colin,

The voltage on the 'collector' together with the voltage on the front mesh of the storage tube depend on a +600V supply derived from a separate winding on the HV transformer. So the lack of +150V on the collector traces back to the lack of -1475V on the CRT.

The usual suspects for failure of the -1475V are the heat-sinked drive transistor Q1195 and the power supply decoupling components C1198 and L1198. Q1190 is also worth checking and C1224 (is it one of the failure prone tantalums?) will kill the drive to Q1195 if it (ie C1224) goes short circuit. There is a fuse in the unregulated supply to Q1195, (F814) which is on the low voltage regulator board.

There are of course other potential failures on the HV side of the -1475V supply.

Regards,

Roger


Re: Tek 7854 intermittent issues

Nick Corvid
 

Not very good at finding things on schematics but I'm fairly sure that the funky looking capacitor is A27C321 I'll have to look through my stuff and see if I have a spare of a decent value on hand. Also if I'm reading things correctly it has to do with the +5 volt rail, but it seems strange that all these issues would be caused by a single sad cap that's kind of out of the way. So I'll keep looking for what is causing these problems in the meantime before I find a replacement and see if that changes anything at all.


Re: Free TWD 120

ykochcal
 

Interesting dead bug looking patch in the last picture
John


Free TWD 120

Thomas Garson
 

My "new to me" TWD120 arrived today. Thank you Charlie.

As Charlie advised in previous email, it did not pass self test, leaving the front panel LED unmistakably solid red.

However, the repurposed IBM laptop external power supply worked admirably so I dove into it.

After removing a number of screws and a cal sticker, I was presented with a single nice and compact SMD loaded PCB. No out-sourced PWM supplies for Tek. The regulator circuitry occupies a compact "can" in one corner.

As I was working w/o a schematic I had to find supply lines on some chips to check voltages. Voltages were good, but one was a bit noisy. DC to DC portion of supply looked good on (Tek 5000) scope. After sniffing around a bit (figure of speech. It did not smell) I noticed several Motorola T10N05e TO-263 type SMD packages near the supply wall, but outside of it. At first I was puzzled as I could find these parts for sale but no data sheet. Figured out they were N-channel power mosfet. I determined they were used for gates to enable/disable DC power feeding from the supply. Interesting. Squinting trough my trusty Swiss Army Knife magnifier (glass lens!) I noticed serious corrosion on the Source solder connection of one of those FETS (Q104: +8v line), which I theorized may have been the source of the noise I has seen. Reflowed the funky joint. Kicked on the power, waited a minute or so for self test to complete: Bingo! LED now turns Green!

That's as far as I got today. Next thing is I have to pull the software for it off of the floppy discs (fingers crossed) for copying over to the server and then burn a back up disk. After that, get my Win98SE PC set up with SCSI (not too big a deal as I used to do a lot of SCSI stuff) and see if I can actually get the thing to work. At the moment, I'm fairly optimistic this will happen in short order.

A few photos here:
https://www.dropbox.com/sh/p0n014thvy22117/AAC3wDTvCpiVvPIIZQY5XTxBa?dl=0

Thomas Garson
Aural Technology, Ashland, OR
By my calculation, the dynamic range of the universe is roughly 679dB,
which is approximately 225 bits, collected at a rate 1.714287514x10^23 sps.


Re: 535 in the Colonies, for only 3,000 CDN pesos

snapdiode
 


535 in the Colonies, for only 3,000 CDN pesos

Roy Thistle
 

If you are in the environs of Calgary, or just plain rich, and intent on getting a 535.... there's one for sale there, for just 3,000 CDN.
And the ad says, it comes with a cart that tilts too!
What a deal, eh.


Front cover for 2225 ?

David Slipper
 

I am looking for a front "clip-on" cover for a Tek2225 but they seem as rare as hens teeth - but it occurred to me that a cover from another scope in the 22xx range may fit.

Can anyone suggest a likely range ??

Before some kind soul offers me one it would need to be in the UK or Europe otherwise the shipping costs become prohibitive :-(

Best regards,
Dave

9681 - 9700 of 181236