Date   

Re: 454 Fireworks Followup

Richard R. Pope
 

Sean,
I would use Mouser or Digikey. I trust both of them. I don't trust E-bay or Amazon for electronic components.
GOD Bless and Thanks,
rich!

On 3/25/2021 12:00 AM, Sean Turner wrote:
Jeff,

Thanks, maybe I'll go with Mouser. I order stuff from them with some regularity, and that's not a horrible price IMO. Amazon is right out...too much counterfeit garbage. Though it might be fun to get some of both and compare their characteristics.

Sean

On Wed, Mar 24, 2021 at 09:56 PM, Jeff Dutky wrote:

Sean,

Or Amazon: https://www.amazon.com/s?k=2N3442

I'm not sure Amazon is really any more reliable than eBay, but just so you
know your options.

I did find 114 count 2N3442 and 951 count 2N3442G in stock at Mouser, both
available in qty 1 for about $6.75 each, so you have an option of a reputable
source, but it comes with a price (the stuff on Amazon is about $2 each, but
you get what you pay for, maybe)

-- Jeff Dutky



Re: 454 Fireworks Followup

Sean Turner
 

Jeff,

Thanks, maybe I'll go with Mouser. I order stuff from them with some regularity, and that's not a horrible price IMO. Amazon is right out...too much counterfeit garbage. Though it might be fun to get some of both and compare their characteristics.

Sean

On Wed, Mar 24, 2021 at 09:56 PM, Jeff Dutky wrote:


Sean,

Or Amazon: https://www.amazon.com/s?k=2N3442

I'm not sure Amazon is really any more reliable than eBay, but just so you
know your options.

I did find 114 count 2N3442 and 951 count 2N3442G in stock at Mouser, both
available in qty 1 for about $6.75 each, so you have an option of a reputable
source, but it comes with a price (the stuff on Amazon is about $2 each, but
you get what you pay for, maybe)

-- Jeff Dutky


Re: 454 Fireworks Followup

 

Sean,

Or Amazon: https://www.amazon.com/s?k=2N3442

I'm not sure Amazon is really any more reliable than eBay, but just so you know your options.

I did find 114 count 2N3442 and 951 count 2N3442G in stock at Mouser, both available in qty 1 for about $6.75 each, so you have an option of a reputable source, but it comes with a price (the stuff on Amazon is about $2 each, but you get what you pay for, maybe)

-- Jeff Dutky


Re: 454 Fireworks Followup

Sean Turner
 

Jeff,

Yes, indeed that is the part number on the transistor I removed.

I'm figuring a plain old 2N3442 that is free of defects (I have curve tracers and the test fixture for this case style) should work fine. I want to give it a try at any rate. Apparently this part is still manufactured by Microchip/Microsemi, but it isn't stocked at the usual suspects and is only available in bulk quantities for absurd prices and long lead time. So my options are someone here or ebay.

Sean

On Wed, Mar 24, 2021 at 09:01 PM, Jeff Dutky wrote:


Sean,

I've been trying to find what the selection criteria were for Q1197, which is
Tek part number 151-0209-00, if I am not mistaken. The service manual does say
that it is selected from 2N3442, but when I consult the Common Design Parts
Catalog I do not find 151-0209-00 listed under selected transistors. Further,
in the section that discusses (and tries to dissuade engineers from using)
selected parts it sounds like a selected part should have a part number
starting with 153- rather than 151-. It also sounds like there are a
population of 151-****-89 parts that are still considered "selected" in the
sense that while they have failed the selection criteria, they have been
checked to be free of other faults, and so are considered higher quality
parts.

Could it be that Q1197 is from the latter population of selected parts and
that the -89 suffix was not yet in use when the 454 was designed? Maybe any
old 2N3442 would suffice, so long as it was working?

-- Jeff Dutky


Re: 454 Fireworks Followup

 

Sean,

I've been trying to find what the selection criteria were for Q1197, which is Tek part number 151-0209-00, if I am not mistaken. The service manual does say that it is selected from 2N3442, but when I consult the Common Design Parts Catalog I do not find 151-0209-00 listed under selected transistors. Further, in the section that discusses (and tries to dissuade engineers from using) selected parts it sounds like a selected part should have a part number starting with 153- rather than 151-. It also sounds like there are a population of 151-****-89 parts that are still considered "selected" in the sense that while they have failed the selection criteria, they have been checked to be free of other faults, and so are considered higher quality parts.

Could it be that Q1197 is from the latter population of selected parts and that the -89 suffix was not yet in use when the 454 was designed? Maybe any old 2N3442 would suffice, so long as it was working?

-- Jeff Dutky


Re: S-1 transient response problems

 

Thanks :)

While comparing the S-1 to the S-2, I discovered another reason to prefer the diodes I used.. I was swapping cables around and plugged the avalanche pulser (at least 10 volts) into the S-1 without the 10x attenuator! Oh my, I said, and yanked the power lead to the avalanche supply as soon as I saw the trace shoot off the screen...

So I put the attenuator on the CORRECT side of the divider tee and the S-1 still works. I am sure the original diodes would have bit the big one instantly. Also glad I didn't do that to the S-2!


Re: S-1 transient response problems

Tom Lee
 

Congratulations on getting it all working, Charles. Another victory for persistence!

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 3/24/2021 20:42, Charles wrote:
Thanks... but I broke the nylon holder, and those diodes are rather prone to destruction (which is how I got the S-1 in the first place). Also they are REALLY tiny and I just don't have the mechanical skill to work with them - in fact I broke a lead, on the remaining good one of course, just removing them from the holder. I decided that more recent diodes could be substituted, and SOT-23 packages are about as small as I'm comfortable handling... and don't forget that they are available from electronic suppliers like Digikey, instead of (50+ year old) dwindling Tek parts stashes.

Anyhow, I finally found the problem... the push-together connectors carrying the trigger from the sampler board pickoff to the preamp board were just barely mating. So when they parted, the center pin(s) were so close that there was enough capacitative coupling to send a fast pulse to the trigger amp, but way too small for the blowby compensation circuit. Verified with scope. On further investigation, the case is supposed to have four "wiggly" long spring strips to make contact with the ground planes on the outside boards, and presumably to also keep a tiny bit of pressure on the connectors at issue! There were only three, and the missing one was on the side where the problem is. I moved one strip to that slot, reassembled and everything's working fine again :)

p.s. to dan: the notorious R18 (36 ohm) was 37.7 so I left it alone :)




Re: S-1 transient response problems

 

Thanks... but I broke the nylon holder, and those diodes are rather prone to destruction (which is how I got the S-1 in the first place). Also they are REALLY tiny and I just don't have the mechanical skill to work with them - in fact I broke a lead, on the remaining good one of course, just removing them from the holder. I decided that more recent diodes could be substituted, and SOT-23 packages are about as small as I'm comfortable handling... and don't forget that they are available from electronic suppliers like Digikey, instead of (50+ year old) dwindling Tek parts stashes.

Anyhow, I finally found the problem... the push-together connectors carrying the trigger from the sampler board pickoff to the preamp board were just barely mating. So when they parted, the center pin(s) were so close that there was enough capacitative coupling to send a fast pulse to the trigger amp, but way too small for the blowby compensation circuit. Verified with scope. On further investigation, the case is supposed to have four "wiggly" long spring strips to make contact with the ground planes on the outside boards, and presumably to also keep a tiny bit of pressure on the connectors at issue! There were only three, and the missing one was on the side where the problem is. I moved one strip to that slot, reassembled and everything's working fine again :)

p.s. to dan: the notorious R18 (36 ohm) was 37.7 so I left it alone :)


Re: S-1 transient response problems

Craig
 

You can find the likely part numbers for the original diodes in the "Tek schottky Diodes memo" in the reference materials files on Tek Wiki.
Specs for many of the part numbers are in section 12 of the Semiconductor common design parts catalog also on tek wiki.
Craig


Re: 2230 PSU Replacement Component Choices

Bert Haskins
 

On 3/24/2021 5:25 PM, alastair.knights@gmail.com wrote:
Hi Bert,

Thanks for supplying your experience. Yes, I may be going overboard, but the long repair stories on the EEV Blog bring out the preventative engineer in me!

The RIFAs capacitors in my input filter already have cracks (are will be replaced), and an open-circuit focus chain resistor was the original fault when I got the scope.
When I replace these resistors I replace the high value ones with two resistors of half the value in series to split the voltage drop.

They seem to last longer that way.


Thanks again,

Alastair




Re: S-1 transient response problems

 

Thanks, Ed & dan. I will check R18 in particular. But I apparently have overthought the problem. It's mechanical, not electrical! I posted three pics in "Sampling with 3S2" (and set the order to most recent first, to save you thumbing through in alphabetical order).

I carefully adjusted the pots (ALL of which interact, what a PITA) as in the manual. Since I don't have a really fast edge, I used my ~600-650 ps pulser edge and set it to display ~750 through the S-1, which should be close to 350 ps risetime. Going back to the 1 MHz square wave, it looks like crap as I initially described. Not only that, suddenly the transient response pot wouldn't do anything either! But flexing the preamp board the right way caused it to pop into flatness (second pic). Now I just have to find the bad solder joint (or carbon comp resistor)...

The slight ripples in the S-2 are probably because I haven't adjusted it either - or possibly from the 114, cables and adapters, and too fast to see on my 60 MHz scope mainframe)... I'd try my delicate S-4 but it has a new hybrid and hasn't been readjusted either! Guess it's time to buy a Leo Bodnar pulser :)


3 photos uploaded #photo-notice

TekScopes@groups.io Notification <noreply@...>
 

The following photos have been uploaded to the Sampling with 3S2 album of the TekScopes@groups.io group.

By: Charles <charlesmorris800@...>


Re: S-1 transient response problems

Dan G
 

Hi Charles,

I have had multiple S-1 and S-2 heads with transient responses that could
not be leveled. In all but one case, the problem was caused by R18 that
had drifted high by 100% - 150%. It also caused increased signal noise,
especially with the sampling head case removed. (All my sampling heads
still have original diodes, though.)

I thought I'd mention this, as it is quick and easy to check, and fairly easy to fix.


Good luck,
dan


454 Fireworks Followup

Sean Turner
 

Quick update: I was able to remove Q1197 from the +75V regulator circuit quite easily by loosening the power transformer and taking the rear panel off to go in through the fan opening. Threw that bad boy on the 575 and it is definitely shorted!

According to the manual, this is selected from 2N3442. Anyone have a spare one or two of those laying around they would be willing to part with, that are known good, before I take my chances on ebay? Willing to pay a reasonable fee + your cost to mail.

Thanks!

Sean


Re: 485 super weak brightness control

Ozan
 

I measured A sweep A Gate B sweep B gate

In the long times all the A sweep A gate and B gate are exactly the same
length and correct but there is no B sweep at all.
What is the B sweep voltage level when there is no sweep?


As the things go to the ns range the zeroed B offset starts to show so it's
slightly delayed but more importantly the B sweep at one point doubles on
its amplitude and starts having a flat top (saturation) from then on its
Both A and B sweep are expected to reset to +13V and should go down from that level when gate starts. When you say it doubles does it always start from +13V but end at different voltages (i.e. delta-V is double) or does the top start from a different voltage? Top should be flat if you are looking at sheet <11> (there is inversion if you are looking at A-sweep at the BNC, then bottom should be flat).

I'm wondering if its best to wait for the relays and continue
troubleshooting after that it if there is something we can tackle in the
meantime while I source needed parts
Please see my earlier comments about the relays, did you test them off the board? The relays are supposed to be off until timebase > 200ns, you can pull them off and debug 1ns-100ns range. However, it is up to you if you want take a break and work on something else.

Ozan


Re: Persuading a 7S12 to play nice with a 7934.

Albert Otten
 

... or it was wrong in the Rev. 1985 manual? There the schematic says Q694 is NPN while the parts list says PNP. It's long ago that I ran into this. Albert


Re: Persuading a 7S12 to play nice with a 7934.

Albert Otten
 

Hi Richard,
W.r.t. to your final question: Which manual are you using? In my paper manual (rev. March 1984) the labels Q690 and Q694 at <7> are wrong (interchanged). The internet pdf (Rev. March 1985) is correct and also shows P600 for interdot enable/disable. Albert


Re: 2230 PSU Replacement Component Choices

alastair.knights@...
 

Hi Bert,

Thanks for supplying your experience. Yes, I may be going overboard, but the long repair stories on the EEV Blog bring out the preventative engineer in me!

The RIFAs capacitors in my input filter already have cracks (are will be replaced), and an open-circuit focus chain resistor was the original fault when I got the scope.

Thanks again,

Alastair


Re: 2230 PSU Replacement Component Choices

Bert Haskins
 

On 3/24/2021 12:18 PM, alastair.knights@gmail.com wrote:
I’d be grateful for comments on my component choices below, which are for an upgrade of my 2230 PSU as per Tek’s Product Modification 060-2239-03 (‘Q935…Q9070 Replacement’). Although my scope works, I’m wary given some of the cautionary tales told in this group and the early SMPS design concepts used and improved on by Tek over the years.

The Tek modification involves replacing most of the critical semiconductors in the pre-regulator, crowbar and inverter, so correct component choice is vital. Your comments and the reasons behind the advice would be welcome. NB In the UK the mains can be up to 245Vac, which affects component voltage ratings in the pre-regulator.

Circuit Ref, ‘Tek description’, originally specified (as fitted in italics) part, my suggested replacement, followed by my reasons for selection:

Q935, ‘Thyristor, SCR 8A, 200V sens gate, TO-220’, C10682X283 (GE C10682), ST Micro TS820-600T – An old GE datasheet for the C106 series lists the ‘On’ condition with 1mA of gate current and the TS820-600T has Ig and Vg as 0.2mA and 0.8V respectively, together with higher voltage and current ratings. NB R935 will shunt the first 6mA of any leakage in VR935 and CR948 before Vg reaches 0.8V.
Ref. - https://www.st.com/resource/en/datasheet/ts820.pdf

Q946 and Q947, ‘Transistor NPN, 50V, 150mA, 200mW, inverter’, SJE389, On Semi MJE15032G – The manual shows 80Vp-p swings at Q947c and the later TIP31C fitted was rated at 100V and 3A. The MJE1503G is rated at 250V for extra margin and has a greater SOR (safe operating area) than the TIP31C (some obvious replacements don’t). The hFE is a bit higher at 100 rather than 40 for the TIP31C but as close as I could find while having the higher voltage and SOR rating. It’s not obvious how or if a higher hFE would affect operation of the inverter and I can’t model it, hence my caution. Ft is higher at 30MHz but hopefully that won’t be a problem.
Ref. - https://www.onsemi.com/pdf/datasheet/mje15032-d.pdf

Q9070, ‘MOSFET, N-channel, TO-220’, STP3000 (Motorola 8630), Toshiba TK10E60W – The Toshiba TK10E60W has higher voltage and current ratings, while keeping the Rds On, gate capacitance and gate charge below that of the IRF730 Tek suggest as a replacement. The gate threshold voltage is within range and modelling in LTSpice suggests it should work well.
Ref. - https://toshiba.semicon-storage.com/info/docget.jsp?did=13500&prodName=TK10E60W

VR935, ‘Zener, 51V, 5%’, SZG35009K7 (1N978B), Nexperia BZX79-C51, 143 - It is not obvious why the original is being replaced, but the mod sheet says all listed components should be replaced. A low power 500mW Zener is indicated to ensure that the full 51V develops when a few mA passes through it. My PSU already has a 1N978B fitted, so I’m strongly tempted to leave it in, given that it shouldn’t be under stress and the available replacements don’t appear to offer an advantage in performance or reliability.
Ref. - https://assets.nexperia.com/documents/data-sheet/BZX79.pdf

CR907 (and CR906), ‘Rectifier diode, silicon, 400V, 1.5A, 50ns’, DSR3400X (BDY73), Vishay MUR460 – The Tek modification sheet recommends 2 x BYD73G in parallel, which makes sense given their rating. LTSpice modelling shows currents of around 1.7A ave and 1.8A rms in CR907. I have a single BDY73G fitted which sounds unhealthy, so the MUR460 looks better with its 4A and 600V ratings, together with a short 50ns recovery time.
Ref. - https://www.vishay.com/docs/88686/mur440-e3.pdf

Finally, I’m reluctantly replacing all the electrolytics in the PSU for safety. While the existing capacitors all read okay in terms of value, leakage and ESR, I’d rather not take the risk given the early nature of the design and known component stress in places. I’m also replacing C907 (1uF non-polarised) as modelling shows that this takes a lot of punishment – 1.2A during the ‘on’ period with 245Vac mains – and failure would break a lot of expensive parts!

Everything else is being kept original. I also have a parts list for Mouser is this is of use to anyone.

Sorry for the long post and thanks in advance for your comments.

Alastair Knights
Hi Alastair
FWIW
I have 2221A 2230, 2232 2235 versions 0f the 22 series Teks.
The only PS failure in any of these has been the line input filter, three so far and counting.
These scopes have only been used on US power.

The only other chronic problem that I've had with these is the focus resistors.


In the past I have had many! PS problems in the 2213, 2215, and the 'A' versions of these models.

YMMV.

Bert


Re: 485 super weak brightness control

Ondrej Pavelka
 

I did lot of measurements and there are two steps where the gate timing
goes wrong. These are associated with relay. I am trying to find some
relays to buy but the guy in the UK I used before now brexited and doesn't
deliver to EU. I hope I can persuade him.

Sadly I forgot them at the workshop so it'll have to wait until tomorrow.

I measured A sweep A Gate B sweep B gate

In the long times all the A sweep A gate and B gate are exactly the same
length and correct but there is no B sweep at all.

As the things go to the ns range the zeroed B offset starts to show so it's
slightly delayed but more importantly the B sweep at one point doubles on
its amplitude and starts having a flat top (saturation) from then on its
hard to tell how long the sweep is but generally speaking its similar to A
sweep but gate is much shorter.

I'm wondering if its best to wait for the relays and continue
troubleshooting after that it if there is something we can tackle in the
meantime while I source needed parts

All the best
Ondrej

On Wed, 24 Mar 2021, 02:07 Ozan, <ozan_g@erdogan.us> wrote:



Tomorrow I'm going to make a table with gate times both A and B at each
setting.

I observed today the gate width was same as 1ns on 10ns and 100ns, there
must be some logical explanation for that?
Can't think of an easy explanation. When you are making the table could
you also mark down both A gate width and B gate width while you are
measuring B sweep timing? Also please observe if you really see a fast
sweep when gate is shorter than expected or if the gate is cut short. If
you apply a signal you can tell from the screen whether sweep is complete
but fast or if it is truncated.

Ozan






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