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Tam

Your video is most entertaining and well explained.
Well done!

The documentation accompanying my kits is spot-on, with all the correct codes and descriptions fully matched, ensuring the fastest possible clearance.

Menahem

I misspoke. It looks that that particular .bin file can't be downloaded for some reason.

Luckily, 160-3493-00 / IC U2400 (I mistyped the p/n in my previous post) is socketed and there no need to desolder. I'm going to remove the IC and clean the IC pins and socket and see if that helps things any. I'll also try to swap the IC from my 2245A if cleaning it doesnt work. If that works, someone from the list has a parts 2246 with the needed IC.

Thanks all!

Hi Vladimir and all

For the purpose of helping others who may have to tackle similar repairs, here is my report:

It should first be noted that there are at least two types of power supplies: an older model using discrete standby circuitry, the schematic being the one mentionned by Vladimir, and a more recent one incorporating an integrated controller, the one I mentionned.

Some photos of the repair can be seen here: /g/TekScopes/album?id=301696

Initial inspection revealed no voltage across the primary capacitor terminals, which required its removal to access the screw securing the bridge rectifier. It's worth mentioning that significant heat is needed to desolder the larger connections; otherwise, there's a risk of damaging the plated through-holes on the PCB. I used a soldering iron set to maximum temperature, in conjunction with a high-performance desoldering tool featuring strong suction. The Tektronix-branded PCB is of high quality and withstands heat very well.

After replacing the bridge rectifier, I observed that the expected 15V rail, generated by the standby supply, was still missing. I replaced the TOP200 controller with a TOP226—a second-generation equivalent from the same manufacturer—which restored the 15V rail, but the main power supply still failed to start.

I spent some time analyzing the protection circuitry. Disconnecting the various protection subsystems one by one did not resolve the issue. The supply remained stuck in a "hiccup" mode—operating for approximately 10 milliseconds once per second. This short active window allowed for probing and measuring voltages on the power rails.

To better monitor system status, I added LED indicators to the control circuitry. The first LED confirmed presence of the 15V standby voltage. A second LED, triggered via a transistor, illuminated when the voltage on pin 10 of the 3525 PWM controller (available at the cathode of CR9 near the top of the A18 board) was high—indicating that either the overvoltage or overcurrent protection had activated, or that the power supply was shut down.

I then cut away the portion of the PCB that had been completely burned beneath capacitors C47 and C83. Unfortunately, several surrounding traces were also affected by the damage and had to be removed and re-routed using insulated Teflon wire.

Once repairs were completed, the LED indicators confirmed that the unit was still operating in hiccup mode. Nonetheless, I was able to take voltage readings during the brief on-times. These preliminary measurements were mostly within expected ranges.

Next, I connected resistive loads to the dual-row headers labeled P5 and P6: 12-ohm, 2-watt resistors for the 5V outputs, 100 ohms for the 15V lines, and 330 ohms for the 24V rail. With these loads in place, the power supply began operating continuously, enabling accurate measurement of output voltages. All outputs were within spec, except the 24V line, which measured 32V. Since the 24V output is unregulated and rated for a nominal 2.5A, I connected an ammeter and a 10-ohm load to draw current. Under load, the voltage dropped to 22.5V, which I deemed acceptable.

To mechanically reinforce the repair, I used silicone adhesive to secure the replacement capacitors to one of the power supply's metal supports.

After reinstalling the unit, I was pleased to find that the device powered on successfully and passed all self-tests.

Jose Luu <jose.luu@...> added the photo album 784A PSU REPAIR ( /g/TekScopes/album?id=301696 ) : images of burnt and repaired area of a 784A PSU

On Sat, Apr 5, 2025 at 05:21 AM, Jay Czaja wrote:

I have a question. What is the best way to measure ripple on the LV supply.
When I checked it the first time, I had the 2247A on an isolation transformer
with my 2245A connected directly to mains AC. I used a x1 probe on my 2245A to
check for ripple and clipped the ground lead of the probe to the chassis of
the 2247A.

No need to use an isolation transformer to float the scope for this measurement. The chassis of the scope is grounded normally, not like old CRT TVs or monitors that mostly had a "hot" chassis.
Just use your other scope, set it to AC coupling and go as low in attenuation to get a readable signal across the power rail being tested. Connect the probe to ground and the tip to the power rail and see how much noise level you measure. You might also want to switch in the 20MHz bandwidth limiter so as to possibly get a more cleaner and relevant display. Ideally use a X10 probe, but X1 should be ok.

On Fri, Apr 4, 2025 at 03:23 PM, Jay Czaja wrote:

I found also this part number 160-2393-00 on the following 2245A "TekWiki"page
and there appears to be a ROM image. Is this something that would be abled to
be downloaded and programed?

You could download that BIN file and program it into a new prom chip. Perhaps the existing one is flaky, hence the come and go error?

This scope has me scratching my head. I had it running all night without any problem, I doubt part number 160-2393-00 is actually the culprit despite the occasional startup error. I suppose I should scrutinize the PSU more.

I have a question. What is the best way to measure ripple on the LV supply. When I checked it the first time, I had the 2247A on an isolation transformer with my 2245A connected directly to mains AC. I used a x1 probe on my 2245A to check for ripple and clipped the ground lead of the probe to the chassis of the 2247A.

Would it be more accurate to connect the probe ground to the ground on the LV test header (J1204) instead of the chassis?

Hi Alberto!

Your scope powers up correctly. The SRQ light stays on because a power cycle was detected. This can be cleared via GPIB or the Keyboard (see manual).
You can ignore this.

As far as I can see there a two errors:

1: ? think the trouble with the jumping/collapsing display is an analog problem - most likely a very simple fault like a dirty/defective potentiometer.

2: The keyboard section is not that complicated. It's descripbed in the "Theory of Operation" section of the service manual.
You should be able to diagnose it without the signature analyzer. Check the wiring to the front panel first.

Holger

Tnx Holger (and others)!

I will study more deeply the service documentation, because I didn’t note an easier troubleshooting approach to the digital section. I am just equipped with the signature analyzer, but I understood that it was not the only tool…

If you are curious about the issue that I need to fix, you can visit my Webpage that I’m dedicating to my 7854:

Alberto

The simple solution is just boycott the USA.

Dear Barry

Suggest you read the excellent Tektronix Circuit Concept book on oscilloscope CRTs, and learn about the development and characteristics of mesh dome CRT.

Then follow the service manual on calibration for the CRT, and HV circuits

Jon

I have a bit more info. I started the scope up again and I got the initial interrupt error that I posted in the beginning of this thread.

When I shut it off and started it back up, I was able to read the error message on the screen. It read "PART NUMBER 160-3493-00"

I was able to find this in the service manual and it appears to be a microcontroller. "MICROCKT, DGTL:8 BIT MICROCOMPUTER, MASKED FOR READOUT SYSTEM"

Is this a part I would need to find a donor scope to scavenge from?

I found also this part number 160-2393-00 on the following 2245A "TekWiki"page and there appears to be a ROM image. Is this something that would be abled to be downloaded and programed?

Jean-Paul and Raymond,

Is there anything that can be done to improve this behavior? I was thinking that reducing the sensitivity of the intensity adjustment might help.

Thoughts?

Barry

Hello,
For all those of you new to customs - in Europe we had it for 20 years.

Small video is at <> which should answer some questions.

Tam

--
With best regards
Tam HANNA (emailing on a keyboardless handset....again)

Enjoy electronics? Join 21k4 other followers by visiting the Crazy Electronics Lab at

Noise may be HV corona

j

Dear Menecham:

Very timely note, suggest to repost on Tekscopes2 and BUY/SELL forums. Perhaps also EEVblog?

We have seen congress in US proposing removing the deminimus exemption. The entire customs/tarrifs is in flux.

Chel the CBP/USPS/Fed Ex for latest info.

Our personal and corporate inports/shipping expericance

1/ The declaration of CoE, Harm # and exact descr is critial to get fast and correct clearance.

2/ Imports of USA CoE are NOT tarriffed by USA regardlss fo the export country,

3/ The reciever in USA may have a tax/tarriff levied by the shipper/US CBP, wheri must be paid before seivery.

4/ The amount is ENTIRELY at the descretion of the government office/worker that clear the shipment, and varies randomly......

High value shipments arealways examined , small packages and lw value MAY be taxed.

Best plan: Fill exact customs decalr with carefully choosen HARM number and country of origin with descr matche HARM # exactly.

Just my experince since 1970s of internation shipping


SHALOM!

Jon

Alright, so I'm not in the clear with this 2247A. I've been busy with other things and had the scope off for about 3 days. Turned it on this morning and noticed the trace was a little noisy without a probe connected and I also noticed a very faint high pitch noise that I haven't heard before. I didn't think much of it but after being on for about 5 minutes, the scope locked up and all of the LEDs in the horizontal section were off and all controls were unresponsive. When I turned the scope off, I noticed the screen displayed a little square that disappears, almost as if something was being discharged. I really don't know how I can explain it but usually when I turn the scope off, the display just turns off. I noticed this screen aberration when turning the scope off when I initially observed the lockup/error problem.

When I turned it back on, the high pitched noise was no longer present and it hasn't locked up again. The high pitched noise would point to something in SMPS, or at least I would think. Any idea how I can troubleshoot this further? My though was to leave the scope off for another few days , take the chassis out before restarting it and then if I get it to fail, check the voltages and see if anything looks to be out of spec. It seems like the scope doesn't like a cold, cold start and the failure disappears after the scope stays on for a bit. Almost seems like one (or more) of the caps are borderline.

Thoughts?

I have a sleepy-eye assembly, switch attached to cable, if interested. I got it from the Tek Country Store (Tek salvage and surplus). It appears to be unused.
Photographs at

/g/TekScopes/album?id=301673

Clark

Raymond! YES I mewant CRT expansion mesh, the SC504 have it bad, due to CRT geom, the SC501/2/3 do NOT

Cheers


Jon

I've had a couple of enquiries from US members here, requesting clarity on the new Customs Duties - which may or may not be applicable on my 24xx series Tekscope kits, which are shipped from here in Jerusalem, Israel.

For PERSONAL imports, which is EXACTLY what these are, when you buy the kits from me, there is what's called in Government language, a "De Minimus" level of US$800.

That means that any PERSONAL import (in this case, up to 3 kits) from Israel to the USA is EXEMPT from US Customs Duties, when the value is less than US$800, and 17% when the value is more than US$800.

Commercial imports (which these kits are not, unless you buy a number of kits for a commercial enterprise) from Israel are taxed at 17% from the first Dollar, irrespective of the value.

So, the bottom line is that if you (a US Resident) buy 1 or 2 kits from me, valued at about $70 each, then you are exempt from the new US Customs Duties.

I hope this helps to clarify the issue!

Regards

Menahem Yachad
www.condoraudio.com