Date   

Re: 7704A (et. al.) Inverter Regulator Question

Mark Vincent
 

Barry,

Goran is right about that area. VR3147 being open will throw the circuit off. C3127 and C3129 are marked ,1mfd. Some models use 1mfd in this place. I have replaced mine with the 1mfd 63V film types because the ESR of the originals was too high causing too much ripple and low B+. After replacing the parts, the B+ voltages at the pins on the 0067 IC were correct. These parts can be checked while the parts you have on order are being shipped. I also replaced the 1 and 2mfd electrolytics on the inverter board with film types of a higher voltage. The originals were bad in mine.

Mark


Re: 465M

Bert Haskins
 

On 9/13/2021 12:16 PM, Michael W. Lynch via groups.io wrote:
On Mon, Sep 13, 2021 at 10:57 AM, Michael wrote:

I have owned one for many years. It still works perfectly. I mainly use it for
stereo and hf transceiver repair work.
Oh, Yes. Even though they are not as rugged as the other 4XX series, they are lighter and just as competent in performance. TEK certainly did not cheap out in the performance department. I like my 455 for many tasks and find it to be a fine scope as well.
I have had a total of six.

Now it's one plus a parts mule which could be restored if I could find a handle with all hardware.

The one that's complete serves mainly as a display for any of my many curve tracers.

A huge advantage of the 465M is that if it's the lower scope in a stack, you don't have to worry about blocking any heat vents.


Every one of these had bad 2.0 and 2.2 caps in the horizontal power supply section!

- Bert


Re: Tektronix 067-1338-0x calibration step generator for SD-series sampling heads

Sergey Kubushyn
 

On Mon, 13 Sep 2021, Ken Eckert wrote:

Thought this might be of interest................

https://www.ebay.co.uk/itm/384042630024?
That "Add to basket" on UK site is a charm :)

---
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* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
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Re: 7704A (et. al.) Inverter Regulator Question

n4buq
 

Until I get that bad transistor replaced, then I don't plan on trying it connected to the display unit as a load. I tried that before I was aware of the bad transistor. Once I get that, I do plan to test it connected to the display unit. If it's still ticking, then it's either a problem with the display unit or the PS. In that case, the external load resistors will at least eliminate the display unit from the equation. I'll report back once I get the transistor replaced.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Göran Krusell" <mc1648pp@gmail.com>
To: TekScopes@groups.io
Sent: Monday, September 13, 2021 11:29:02 AM
Subject: Re: [TekScopes] 7704A (et. al.) Inverter Regulator Question

Hi, I have not followed this discussion very closely but my guess is that you
are looking in the wrong direction.

You need to check U3105 pin 2, BAL SENSE, where the voltage should be 0V in
normal operation. If it deviates more than 200mV (+ or -) then the PS should
turn off.

Also check U3105 pin 13, I SENSE, where the voltage shall be positive,
perhaps +0.23V, in normal operation. In an over-current situation the
voltage drops below 0V and the PS should turn off.

If you hear a hissing and sparking sound you may have a problem with your
voltage multiplier.

Carry on and good luck
Göran






Re: 7704A (et. al.) Inverter Regulator Question

n4buq
 

Very good! I appreciate the link.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Ozan" <ozan_g@erdogan.us>
To: TekScopes@groups.io
Sent: Monday, September 13, 2021 11:28:36 AM
Subject: Re: [TekScopes] 7704A (et. al.) Inverter Regulator Question

Following link also has debug information on 7904 PSU which may contain
useful information for 7704A PSU:
https://w140.com/Tek_7904_Power_Supply.pdf

Ozan






Re: 7704A (et. al.) Inverter Regulator Question

Göran Krusell
 

Hi, I have not followed this discussion very closely but my guess is that you are looking in the wrong direction.

You need to check U3105 pin 2, BAL SENSE, where the voltage should be 0V in normal operation. If it deviates more than 200mV (+ or -) then the PS should turn off.

Also check U3105 pin 13, I SENSE, where the voltage shall be positive, perhaps +0.23V, in normal operation. In an over-current situation the voltage drops below 0V and the PS should turn off.

If you hear a hissing and sparking sound you may have a problem with your voltage multiplier.

Carry on and good luck
Göran


Re: 7704A (et. al.) Inverter Regulator Question

Ozan
 

Following link also has debug information on 7904 PSU which may contain useful information for 7704A PSU:
https://w140.com/Tek_7904_Power_Supply.pdf

Ozan


Re: FG502 No wave

Ozan
 

Hi Chris,
There could be multiple issues. You can jump to “Collector voltage at Q315 = -0.6V at Q325 = -3.5V.” if you are looking for a quick answer.

Turn the dial so that output (pin 6) of U135 is about +10V, pick triangle waveform, pick 10^3 range.
I cannot quite get to +10V and the dial was set to maximum which is +9.8V.
Earlier you measured 7.28 to 19.7V which is about what is expected. Although 9.8V is fine for analysis something seems to be wrong with R110, is the pot securely mounted with no loose nuts? This is not the root cause of the “no oscillation” problem but something that needs to be debugged separately later.

Voltage across R140 = +2.66V, across R175 = -2.52V, measured with + of DVM probe on collector of transistors.
Thank you for giving the + reference, it eliminates any ambiguity. This says up and down currents are about 5mA. There is slight mismatch in currents, and the value is higher than expected but this should still make the circuit oscillate. This step eliminates the current source circuit as the suspect. We can re-visit the currents when you fix R110.

Collector voltage of Q292 = +0.15V, R155 is quite hot and voltage at supply side is + 16.23V. No sign of any wave.
Collector of Q292 should be either +5V or -5V (comparator output) in normal operation. +0.15V is not right but see below. R155 burns 16.23^2/820=0.3W. Should be warm but not very hot. If it is getting really hot you may want to measure its resistance, we are looking for much smaller than 820-ohm so in circuit testing can give you an idea. See the next item before checking it though.

Collector voltage at Q315 = -0.6V at Q325 = -3.5V.
This portion is the “gate function”. This is (one of?) the reasons for stopped oscillations. If collector voltage of Q325 is -3.5V it will turn on Q315 and it will clamp collector of Q292 to stop the oscillations. You can short collector of Q325 to its emitter with a piece of wire, if you get waveforms out then this is it.

As for debug:
I assume nothing is connected to the “GATE IN” BNC.

Base of Q332 should be about two diode voltages above ground ~ 1.2-1.4V. This should turn off Q332 and turn on Q330 which supplies base bias to Q325. Base of Q325 should be one diode drop above is emitter (0.7V above -17V). This should turn on Q325 and make its collector voltage ~ -17V. You are measuring -3.5V so something is not working. In normal operation Q315 should be off but in your case I suspect Q315 is on. You can confirm by measuring voltage drop across R318 which should be 0V in normal operation.

I recommend measuring base, emitter, collector voltages of Q325, Q330, and Q332.

Rest can wait until this is debugged. Your “GATE” circuit is gating off the oscillations.

Base voltage of Q230A = +0.14V (for reference base voltage at Q230B = +.05V) Both A and B were checked out of circuit and appear to be OK.
Base of Q230A is OK given other side of the bridge is at +0.15V. Base of Q230B depends on emitter voltage of Q210, which is OK for your measurement below.

Gate voltage of Q200 = +7.9V fixed i.e.. not going up / down. Please confirm that the gate connection is what would be the base if it were a transistor.
Yes, you can think gate of a JFET similar to base of a transistor. Just to make sure: gate terminal is the one connected to cathode of CR145 and anode of CR175. I suspect this measurement is not at the gate of Q200 because of the following point.

Emitter voltage of Q210 = +0.16V This transistor gets very hot (not unexpectedly, as it is fitted with a heat sink). Q204 also gets very hot.
Emitter of Q210 should try to follow gate of Q200. We expect gate of Q200 to be ~ 0.15V and the emitter is at 0.16V which would be correct if we ignore the 7.9V measurement.

Could you confirm gate voltage of Q200 again, which is the same node as cathode of CR145 and anode of CR175.

Ozan


Re: 465M

Michael W. Lynch
 

On Mon, Sep 13, 2021 at 10:57 AM, Michael wrote:


I have owned one for many years. It still works perfectly. I mainly use it for
stereo and hf transceiver repair work.
Oh, Yes. Even though they are not as rugged as the other 4XX series, they are lighter and just as competent in performance. TEK certainly did not cheap out in the performance department. I like my 455 for many tasks and find it to be a fine scope as well.

--
Michael Lynch
Dardanelle, AR


Re: "mottled effect" on anodized front panel

Greg Muir
 

I’ve seen similar effects from contaminated anodizing solutions. If the rinse is inadequate after the item leaves the electrolyte bath some of the acid can remain in the porous aluminum oxide layer during sealing. Over time the remaining acid can slowly affect the finish.

Greg


Re: 465M

Michael
 

I have owned one for many years. It still works perfectly. I mainly use it for stereo and hf transceiver repair work.


Re: "mottled effect" on anodized front panel

Chris Wilkson
 

On Sun, Sep 12, 2021 at 09:34 AM, Tom Norman wrote:


The
product I used is called Novus, but I don't recall if it was the #2 or #3 (#3
is least aggressive).

Slight correction...Novus #3 is the MOST aggressive. Beware!

Novus #1 is for cleaning and polishing. It's non-abrasive and pretty safe.
Novus #2 is for fine scratch removal and heavy cleaning. It is mildly abrasive and will damage fine finishes and artwork.
Novus #3 is for heavy scratch removal. VERY ABRASIVE!! It will destroy the finish and remove artwork completely.

Novus is great for restoration and maintenance. Used extensively in pinball and video arcade hobbies and some automotive applications.
Always start with #1. Use #2 gently to remove fine scratches and blemishes. #3 is rarely used...only in extreme restoration cases.


Re: 7704A (et. al.) Inverter Regulator Question

n4buq
 

Hi Albert,

No, I hadn't seen that. I've downloaded that manual and am reviewing those sections. That should be a big help.

Thanks!
Barry - N4BUQ

----- Original Message -----
From: "Albert Otten" <aodiversen@concepts.nl>
To: TekScopes@groups.io
Sent: Monday, September 13, 2021 10:13:56 AM
Subject: Re: [TekScopes] 7704A (et. al.) Inverter Regulator Question

Hi Barry, just in case it escaped your attention: for instance the 7904A
manual contains a more extensive fault finding procedure for the similar
SMPS.
Albert






Tektronix 067-1338-0x calibration step generator for SD-series sampling heads

Ken Eckert
 

Thought this might be of interest................

https://www.ebay.co.uk/itm/384042630024?


Re: help with identity of 7000 series PSU part no 620-0276-00

Brian
 

Hi Hakan , thank you for that info , I'll have to keep looking or try harder to fix the supply in my 7834 which just sits there and ticks .
Brian

On Monday, 13 September 2021, 16:42:35 BST, zenith5106 via groups.io <hahi=telia.com@groups.io> wrote:

On Mon, Sep 13, 2021 at 04:21 PM, Brian wrote:


I am in need of a new or working power supply for my ailing 7834 and I have access to this one 620-0276-00.
620-0276-00 was used in 7104 only and in case of replacement 620-0283-02 should be used.
620-0283-02 was used in 7103, 7104, 7704A, 7854, 7904A and 7934.
No replacement info on 620-0250-00 which was used in 7834 possibly because 7834 went out
of support in 1995.

/Håkan


Re: help with identity of 7000 series PSU part no 620-0276-00

 

On Mon, Sep 13, 2021 at 04:21 PM, Brian wrote:


I am in need of a new or working power supply for my ailing 7834 and I have access to this one 620-0276-00.
620-0276-00 was used in 7104 only and in case of replacement 620-0283-02 should be used.
620-0283-02 was used in 7103, 7104, 7704A, 7854, 7904A and 7934.
No replacement info on 620-0250-00 which was used in 7834 possibly because 7834 went out
of support in 1995.

/Håkan


Re: TCP202 with 15mA of ~150KHz noise.

Andy Warner
 

I tried adding some ferrites with decent impedance in the ~100KHz range to
the +/- 15V rails:
https://photos.app.goo.gl/RaxHFTVdvF6T7LAJA

No significant change, next step repeat for the +/- 5V rails, and if that
doesn’t help, move on to augmenting the decoupling…

On Fri, Sep 10, 2021 at 16:17 Andy Warner <andyw@pobox.com> wrote:

Thank you for the datapoint, I wish I were so lucky.

On Fri, Sep 10, 2021 at 16:08 Raymond Domp Frank <hewpatek@gmail.com>
wrote:

On Fri, Sep 10, 2021 at 07:40 PM, Mark Litwack wrote:


I'll add one additional comment that in looking at the noise with FFT,
there's
a strong 88kHz component in there as well on both probes, so there's
likely
multiple noise sources getting into the probe power supply.
I checked my TDS3000B/TCP202 combination. In normal ‘scope mode, all I
see
is an 88 kHz waveform at about 2 mA pp.

Raymond





--
Andy





--
Andy


Re: 7704A (et. al.) Inverter Regulator Question

Albert Otten
 

Hi Barry, just in case it escaped your attention: for instance the 7904A manual contains a more extensive fault finding procedure for the similar SMPS.
Albert


502A Dual Beam Oscilloscope on Shopgoodwill

Bert Haskins
 

No affiliation I just watch this hoping to see a good 7603 ( not a rackmount ) come up.


Re: Suggestion for our group Administrator

 

FWIW I've seen a spam of microedits just this month on HPAK - and I
barely even read that list.

On Sun, Sep 12, 2021 at 6:43 PM Jim Adney <jadney@vwtype3.org> wrote:

It was just a suggestion, and I believe this list's owners have done a good job explaining why editing causes problems. Many of you clearly have long history with this list that I lack.

I'm very familiar with listservs and I'm also very fond of them. None of the lists I own have as many listees as this one does, and I've never run into the kind of OCD that got brought up here, generating multiple reposts. I was thinking more about the long term problem of having incorrect part numbers, etc. become part of our permanent record. I communicate almost exclusively via email. I reread my messages before sending and make corrections and additions if necessary. Nevertheless, I'm not perfect, so occasional mistakes slip thru.

I take the digest form of this list, and I'm VERY aware of the problems that this can cause if someone top posts and quotes the whole digest with the wrong subject line. I'll never make THAT mistake. Yes, that happens on another list I'm on and it's really annoying. It's good that groups.io has instructions at the top of each digest that discourage this. I've found it hard to add proper replies from the digest, but I'll catch on. Up to now, I've just gone to the web site, searched for the message I want to reply to, and then written my reply. THIS reply comes via the individual message link within the digest. I hope this worked as intended.

I wish groups.io did a better job of showing threads on their web site. They are there, but you have to dig down to find them. That's something we can't fix.




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