开云体育

Given I don't have a schematic for the PSU it would be a bit hard to work out what the components are and what their
values are. Luckily I found a chap on eBay selling replacement PSU's for a small sum so I have one of those on the way.
Once I get that I'll take note of the component values before inserting it in the CRO. I can then take my leisure in
repairing the old PSU.

cheers

Tim

---

The photo of the underside, seems to also show some damage to the solder mask, covering two PCB traces that may have resulted in a short cct (if it was a metal part that did that.) ? As well as the heat damage.

I've repaired stuff like that in the past without drawings, purely by cutting out (by chain drilling and needle file) the damaged PCB, and grafting in some plain bare board, then hard wiring in replacement parts, based on the markings of the old parts.

The last time, that was an old 50/60Hz transformer based thing though, so quite forgiving.? I'd be especially careful with a SMPS, especially on the AC Line connected side, as you need to maintain creepage and clearance spacings of course.

Have Fun, but take care.

Dave G0WBX.

-- 
Created on and sent from a Unix like PC running and using free and open source software:

as Ceasar said, this is a too dangerous way at least for me as you can see I am afraid to even entering keywords. And after your receiver upgrade?up to 6GHz you are using 85046a or 85047a test sets?
Btw, you mention the restoration of CRT from HP 8753B. I have done this a few months ago for HP 1349A. The brightness is now ok just the focus is still not good. Is there a way how to improve it?

On Sun, Apr 5, 2020 at 06:21 PM, <ujonsson@...> wrote:

BIOS s

i downloaded the step by step.? That looks like a great writeup!? I will let you know what I find out.


Ulf

I cant be 100% sure but it is not booting up and when I took the drive out I could at first not read anything from is using a USB-IDE adapter. After some gentle tapping I got it to spin up once and I got some of the files off it.

?I did the drill modification and hooked up a DVD player that I had with IDE to the secondary IDE port on the motherboard and I created a Win 98 SE boot floppy.? ?It boots up from the floppy and creates a virtual disc A: but it is not able to install drivers for the CD player. I probably need to find newer drivers that match the DVD burner.

If I stop the boot and go to the BIOS setup its not showing the DVD player. I also tried to hook up a 5.25" IDE Hard drive to the secondary IDE and that was not showing up in the BIOS either.?I then went in and changed the BIOS to activate the primary and secondary IDE's, hooked up the 5.25 to the primary on board IDE and it tried to boot from it.? It turned out to have Linux on it so it started up GRUB Rescue...? There is hope.? I wish I had a day to focus on it.? I'm working like crazy. I'm one of 4 people in a lab that normally have 600 people in it...

He already has the option keywords and does not need to (manually) program the eeproms.? He just wants the procedure to enter the codes.? Manually reprogramming the eeproms is too dangerous and/or difficult, which is why I provide the keywords to those that want them.? I don't want anyone to accidentally destroy their analyzer.

Hi Matthew,

Nice story... its amazing what some people will do to "improve" the operation of various things.

On a side note I'm also repairing a Wavetek sig gen where ALL the 100uF35v electros have dropped their guts all over the PCBs. Initially I thought it would just be a matter of replacing all the caps but on closer inspection I found that many of the traces and plated holes have been eaten away. So now I'm slowly re-linking various parts of the boards and using very fine wire to reconnect the holes. Its the project I'm working on when I'm not working on something else!

See pics here...



cheers

Tim



--
This email has been checked for viruses by Avast antivirus software.

LOL typo :)

TT

--
This email has been checked for viruses by Avast antivirus software.

I am glad you have a new PSU on the way and plan the fix the existing one. Sounds like a good strategy all around.

One of the strangest "smoked PSU" problems I ever encountered was in a really nice Tektronix 7k mainframe I was repairing for a customer. The customer reported that they had bought a (supposedly working) plugin for it on eBay, but when they plugged the plugin in and applied power, the oscilloscope mainframe emitted popping sounds and clouds of smoke and would no longer work. I received the plugin and mainframe for repair. The source of the smoke was obvious - fuse resistors on multiple PSU rails were toasted. Moreover, even after removing all the plugins those same rails were still shorted (0-ohms) to ground. I kept pulling connectors trying to localize the short until all that was connected to the PSU were the sockets for the plugins, but the short remained. Puzzled, I looked carefully at the plugin sockets with a flashlight, and what do you know, there was something in one of the sockets that looked like crumpled aluminum foil. Using tweezers I was able to extract it and sure enough - crumpled aluminum foil. What's more, with the foil gone the short was gone too. I replaced the burned fuse resistors and everything worked fine, including the new plugin!

Apparently what had happened was the the seller of the new plugin had folded aluminum foil over the PCB-edge contacts in a (misguided) attempt to protect against ESD. The customer, not realizing the foil was there, plugged the plugin into the oscilloscope and POOF!

All is well that ends well I guess.

-Matthew D'Asaro

开云体育

On 4/5/20 7:10 PM, Tim Tuck wrote:

Hi Matthew,

Nice meter,? I think I'll have to add one of those to the repair bench. At the moment I'm using a DE-5000 LCR meter
which does a stellar job of reading things like ESR etc. but I've never tried to use it in-circuit, I've always
de-soldered suspect caps to test.

I've dissembled the PSU and I find that a number of components have incinerated themselves, see pics here...

FYI dissemble does not mean disassemble. You should look it up. (I'm not posting this to the list.) --doug

Given I don't have a schematic for the PSU it would be a bit hard to work out what the components are and what their
values are. Luckily I found a chap on eBay selling replacement PSU's for a small sum so I have one of those on the way.
Once I get that I'll take note of the component values before inserting it in the CRO. I can then take my leisure in
repairing the old PSU.

cheers

Tim

Hi Matthew,

Nice meter,? I think I'll have to add one of those to the repair bench. At the moment I'm using a DE-5000 LCR meter which does a stellar job of reading things like ESR etc. but I've never tried to use it in-circuit, I've always de-soldered suspect caps to test.

I've dissembled the PSU and I find that a number of components have incinerated themselves, see pics here...



Given I don't have a schematic for the PSU it would be a bit hard to work out what the components are and what their values are. Luckily I found a chap on eBay selling replacement PSU's for a small sum so I have one of those on the way. Once I get that I'll take note of the component values before inserting it in the CRO. I can then take my leisure in repairing the old PSU.

cheers

Tim




--
This email has been checked for viruses by Avast antivirus software.

I don't have any specific advice on that model (54720) but I can say that this is the exact situation where a cheap in-circuit ESR meter will pay for itself with a few minutes of use. I have (and really like) the Blue ESR Meter from Anatek (). The idea behind these devices is that they send a low amplitude (<0.7V) AC signal though the capacitor and use that to measure the real (resistive) component of the impedance. When electrolytic capacitors go bad, their ESR usually goes way up so this is a good way of rooting out the bad ones. The low amplitude prevents turning on of semiconductor devices that are in the same circuit (such as rectifier diodes) so the device can be used to (estimate) the ESR of capacitors in-circuit. Of course, there are a lot circuits you can think of where this trick won't work well (a tank for example, or parallel capacitors) but it works well enough for most power supplies that I find mine to be an invaluable troubleshooting tool.

That all said, more recently I have taken to just replacing them all, or at least all the ones in the same circuit, when I start finding bad electrolytic capacitors in something. It seems that often when one is bad, the others aren't far behind.

-Matthew D'Asaro

An easy one for once. These ICs seem to still be reasonably common. Here is probably the easiest way to get one:



-Matthew D'Asaro

This chip is used in the 8663A signal generator UHF Modulator A12A2 board. I would like to buy one, or find out where one could be bought. Might even be in the market for the board itself. Many thanks............Don

Since you have the 934A HARMONIC Mixer whatever you put in to the LO port will give you fairly high level harmonics between 2 and 12.4 GHz. So if you are trying for 10 GHz (-20 MHz or + 20 MHz) you would set the 8640B to 1GHz, set the 8350B system to 10GHz and then fine tune it to 20 MHz lower or higher in freq until the 8709A shows lock, it will be pretty sensitive.? Conversely, if you want a locked 10GHz you would fine tune the 8640B up or down in freq by a small amount - 2MHz (you are turning the 10th harmonic of 1GHz (10GHz) to be the required 20MHz different than the 8350B 10GHz freq.) to achieve lock on the 8709A.

thanks, so the procedure is the same as for 8753E however just to be sure it is written :

"?Perform this procedure only if :?(1) the instrument has option 002 or 006 or 010, AND"
should I worried about the last sentence, and one more hypothetical question what could happen if the codes I have are wrong??

Hi all,

My HP 54720A CRO failed to power on this morning I suspect an electro failure but given the plethora of caps in the PSU I was wondering if anyone had a likely candidate to go take a look at ?

Any other pointers to 54720A PSU repair, gratefully received.

It's a pity that the service manual considers the PSU as a unit and thus doesn't supply the schematic, so if anyone has that, please share :)

thanks

Tim



--
This email has been checked for viruses by Avast antivirus software.

Take a look at?
I think it may have what you need.
--John Gord