R&S CRTU - Need help removing the front panel + questions on broken TFT

[Bicurico]

Hi,

I got myself a CRTU (Thanks!), which has a few problems, one being a non-working TFT.

With a direct light against the screen, I can see the image is still working, it is just the backlighting that is not working. I assume that either the DC/AC Converter board is broken and/or the CFL.

This gives me hope and options for repair: fixing the Converter, replacing the CFL (not sure that would be easy, though) or trying to replace it altogether with LED stripes as described/linked somewhere in this forum.

The last chance would be simply replacing the front module or just the TFT with one extracted from another broken CRTU (with these parts intact, of course).

Anyway: I am stuck with the most stupid thing. I cannot extract the front module.

The service manual says the following for "Replacing the LCD and/or DC/AC Converter in the FRONT MODULE":

Opening the instrument and removing the FRONT MODULE

Switch off the instrument, pull the mains plug and unscrew the rear-panel feet.

Place the instrument onto the front carrying handles, push the tube upwards and take off.

Unscrew the four screws of the front handles at the instrument frame on both sides and take off the front handles.

Unscrew a countersunk screw (if present) at the front on the labeling panel next to the spinwheel and pull off the labeling panel towards the front.

Unscrew two countersunk screws in the front frame at the top and at the bottom as well as twocountersunk screws at the front above the AUX1/2 BNC connectors.

Unscrew a combi screw at the top of the module support for support of the PCMCIA INTERFACE.

After unscrewing the two countersunk screws at the top left instrument frame slightly lift the cover at the top of the instrument, slightly shift towards the right and lift off.

Slightly push the FRONT MODULE from the rear to the front using little pressure.

Note: Note the three ribbon cables for the PCMCIA INTERFACE that are still connected to the MOTHERBOARD1.

After sliding out the FRONT MODULE disconnect the three ribbon cables from the MOTHERBOARD1 connector.

Take the FRONT MODULE completely out of the CRTU Radio Unit.

This is where I don't know what to do and the manual doesn't provide any pictures:


After unscrewing the two countersunk screws at the top left instrument frame slightly lift the cover at the top of the instrument, slightly shift towards the right and lift off.

Slightly push the FRONT MODULE from the rear to the front using little pressure.

What cover???
In what position should I put the device???

What happens to me is that the front module seems to be attached to the input board on the upper right side. If I remove the screws holding the input board, then yes everything wants to slide out, but can't because of all the cables/wires (I did not do it, of course).

As I said, next to the PCMCIA module on the top upper right, both modules behave as if they are soldered against each other.

Is there any trick to it?

I can slide the front module out on the left side for about 15mm, but it won't move on the other side. And yes, I removed the screw holding in the PCMCIA module to the frame.

When I mentioned LEFT, RIGHT, UP, DOWN, I am referring from when you are facing the front side of the device, looking at the screen and buttons.

Any help would be appreciated. I don't want to push with too much force, to avoid breaking stuff.

Thanks,
Vitor

[CJay]

I stripped my CMU down with a good amount of trepidation but it wasn't quite as bad as it seemed.

You need to remove the side handles, then the lettered front panel will come off.

Once you have that removed it will expose the rest of the 'external' screws you need to access to separate it from the input/output connectors .

Make sure you unplug the PCMCIA/Floppy cables.

Remove the main instrument cover and you'll find (from memory) ten or so countersunk screws which hold the 'PC' module in place, you'll also need to remove the screw(s) on the PCMCIA/Floppy bracket inside the instrument.

Once you've removed those screws check for cables (power cable for one) and unplug them.

It should then separate with a little gentle persuasion.

Disassembly of the PC is fairly straightforward but be aware there may be cables inside which are clipped to the cover so proceed slowly and with cautiuon as you'll need to unplug them in fairly limited space.

I've heard of a few inverters failing so it should be an easy fix with luck but the CCFL in mine was a very odd shape (pic in thread linked below) and if that's failed I imagine it'd be rather difficult to source so given the amount of effort required to disassemble it might be an idea to have replacement LED backlight available?

Reassembly, as all the books say, is the reverse of the above procedure, the multi pin bus connectors that connect the PC to the motherboard are well keyed and the fit of the assembly is good enough that it wouldn't be easy to get it wrong and damage them but make sure the PC goes back in, square and all should be well.

The screws on mine were non magnetic so be careful not to drop them inside, it's a heavy instrument so rattling them out isn't easy (don't ask me how I know)

Thread with backlight pic:

https://www.eevblog.com/forum/repair/rohde-schwarz-cmu200-lcd-backlight-success/msg1072224/#msg1072224

[Bicurico]

Thanks.

Thought it should be possible to remove the front module without having to pull out the input connector module (I mean the module with all connectors to the right of the front module).

From the manual I thought one just removed the handles, printed front cover, 4 feet, main tube case and then 2 screws on top and 2 screws on bottom. Take off the two screws of the PCMCIA interface and the bigger screw holding it in place.

Then I expected to pull out the front module. But it doesn't, because it seems attached to the front input module. This is what I don't understand...


Any help is welcome.

Thanks!

[CJay]

Ah, I see.

No,  the N connectors and DB 9s on the CMU stayed behind when the FMR5 came off.

I would expect the CRTU would be the same.

If I can find time I will take some pictures tonight and post them in here (I *think* there may be pictures elsewhere on the forum too)

[richnormand]

Had similar issues with my CMU200.


1)
You need to remove the front panel and inner RF trim to expose all the screws holding the front unit together.
The RF connectors are not part of that assembly but I had to remove ribbon connectors and one or two screws holding the PCMCIA assembly too.
Don't forget to reconnect the front LEDs also...... need tiny fingers there.


2)
"one being a non-working TFT.

With a direct light against the screen, I can see the image is still working, it is just the backlighting that is not working. I assume that either the DC/AC Converter board is broken and/or the CFL."

That was my issue. Turned out to be the smd micro fuse on the inverter board on my unit.

Fuse and inverter references:
http://www.koaglobal.com/ja-JP/product/fuse
CCP2B or CCP2E smd micro fuse

inverter board
http://www.tdk-lambda.com/products/sps/catalog/eng/etl_cxa_l0605a_vjl.pdf

Hopefully that is it and will save you the pain of pulling the actual screen apart.
If it is the lamp that is bad you might consider LED replacements and also check the front glass (shielded) for yellowing.


3)
Finally, while you are in there the small fan on mine was seized and a telltale sticker on a chip was indicating it had been exposed to high temperatures.
Popped the inner fan shaft seal and oiled it. No issues for close to a year now. If yours is similar that is worth checking.

Best of luck with it. I can post photos should you need them

[Bicurico]

Thanks!

I actually just finished disassembling and reassembling the unit.

No fix done, but now I know how to open it: real PITA.

Turns out that the upper right corner of the front panel is actually screwed to the front input module. You need to pull it half out around 10mm, then you can fiddle and remove that screw. That is not documented in the manual.

The power cord is a nother pain. I unscrewed the whole USB PCB. Getting it back, though, was again a PITA.

I opened the front module and everything looked fine. I saw that sticker you refer to, but I couldn't interpret it.

Fans are OK, noisewise, right now.

Let me study the inverter and micro fuse. I am tempted to purchase a whole new inverter board...

Let's see.

At lease I can now open/close the device.

Regards,
Vitor

[Bicurico]

Hi,

Question: If I measure continuity on the micro fuse and it is interrupted, how much of a deal would it be to just remove this fuse and make a short connection?

I don't have any spare CCP2B/E lying around (checked some PCB's) nor do I find anywhere reasonable to purchase them.

The inverter board can be purchased for around 20 Euro, but would take a month to arrive. Hence I am tempted to just short the fuse out, to see if it works. If so, I can still order a new inverter board.

What's the general opinion on this? I feel that circumventing fuses is generally a bad idea...

Regards,
Vitor

[CJay]

I'd agree, but perhaps a pico fuse of 1 to 1.5 amps?

Of course you'll have checked any electrolytics on the inverter already.

[richnormand]

" don't have any spare CCP2B/E lying around (checked some PCB's) nor do I find anywhere reasonable to purchase them."

Yep.


After checking the electrolytics, as pointed out by CJay, I used a generic smd fuse from my kit (cheap assortment from ebay).
My notes say the blown fuse was a cpd2 series KOA 20.
The spec sheet for the TDK board says 1.2A, 1.5 max at 5V input. The other version is 0.8A at 5V. Check the version you have as yours could be a different manufacturer altogether.
The CPD2B is a 1A rated and 2.0A fusing so I guess I have the second version.

My guess is I used a 1.5 or even a 2A.
In the past I have come across several inverter boards like those that had blown fuses.
I use a bench PSU (current limited to say 3A) as input to the board with my DMM on amps in place of the fuse and bring it to the rated voltage (connected to the display lights).
Shorted trans or open FET will be immediately obvious. If it works I use twice the current it takes for the fuse rating. That might be generous but it works.
I figured some transients take the fuse but never had to change a cap.... or have one fail in several years, so your choice

[Bicurico]

Went to my article and picked an old Sony LCD monitor and a Vail laptop. Hopefully I can scrap a useful fuse, though I know it's quite impossible to measure fuses...

Another question:

1. Why would the fuse break?
2. How did you solder/unsolder the fuse? I do have a hot air soldering station, but would like to know how you guys do it.

Thanks,
Vitor

[richnormand]

Your only indication for the fuse is the markings on it and a google search. If not, the method with a power supply while measuring the current to the board (if the board works well otherwise) is another indication.
In my case the TDK board specs gave the input current expected, so a fuse 1.5 to 2x that should be OK.

To remove it I used my soldering iron with a wide blade to touch both pads while feeding a bit of solder.
Then cleaned up with solder wick. Put a small amount on each pad and used tweesers to deposit the new part. Touched each side with a fine point, back and forth.

Hot air pencil is the other option if you shield the heat to the other surrounding stuff.
There are several excellent smd soldering techniques demonstrated on youtube if you are not familiar with this.

[g4wyz6]

So on the inverter board, where is the SMD fuse located?

Recently acquired an CRTU, the LCD is dead.

Regards,

Mike G4WYZ

[g4wyz6]

Hello

I have a faulty inverter board, I've applied an external 5 volts its not drawing any current. The only fuse I've found is SMD one the output.

Can you tell me who the supplier of the CXA-L0605 are please.

73's

Mike G4WYZ

[richnormand]

So on the inverter board, where is the SMD fuse located?

Recently acquired an CRTU, the LCD is dead.

Regards,

Mike G4WYZ

Just follow the 5V trace from the supply plug to the corner where there is a small inductor and a few caps. If you look at my first posting in the thread you will find links to the TDK inverter board layout as well as the fuse spec-sheet with the ID numbers. Should be easy to identify at that point ( smd fuse KOA 20 is a CCP2 series) and you can confirm with a dmm reading across it. Unfortunately I did not take photos when I did the replacement about a year ago. If I remember correctly it only had the number 20 on it.


Hope that will help.

[Bicurico]

Hi,

I ended up repairing the broken LCD by soldering a new non SMD fuse on top of the broken fuse.

To be sure that it is the inverter and not the LCD panel, turn on your device and hold a bright light source against the screen. If the panel is working, you can actually see a faint image on the screen. If this is the case, chances are your inverter is broken.

Look at the attached picture: the red rectangle marks the SMD fuse. Just use a multimeter in continuity mode and see if the fuse is broken.

If so, get an equivalent fuse 1A-2A of the fast kind and solder it on the sides of the existing SMA fuse.

As a plan B I ordered a new inverter board, but I have not used it, yet, as my "repair" was successfull so far.

Here is an example link: http://www.ebay.de/itm/1Pcs-New-For-Tdk-Lcd-Cxa-L0605-Vjl-Inverter-Plc-Module-Q-/232345204100

Please verify prior to ordering it, if it is really the correct version: it has to be a L0605-VJL one, or whatever the version you have is.

Good luck!

Regards,
Vitor

[eb4eqa]

My CMU200 arrived with no backlight either. I changed it to LEDs, a big improvement for this display:

http://www.rbarrios.com/projects/LCD2LED/

And for driving the LEDs:

http://www.rbarrios.com/projects/8753LED/

I have the pictures of the installation I did in the CMU200 somewhere... I attached the regulator next to the high stability OCXO.

Regards,
Roberto

[Bicurico]

Cool!

Please add pictures and further information, i.e. where you got the power from.

Thanks,
Vitor

[jklasdf]

Here are some pictures and notes for replacing the backlight inverter fuse on the CRTU (the CMU200 is slightly different).

The first picture is with the cover and front labeling panel off. Circled in green is the PCMCIA screw bracket. You don't need to remove the two screws on the cover for the PCMCIA slot. (I don't think you need to remove the 3 screws circled in red either even though I did. I think I pretty much removed every screw possible before finding this thread -- 6 on top, 2 on the left, 2 on the right, and 8 on the bottom -- such a pain.)



The second picture shows the location of the (hidden) screw securing the display/computer part to the RF input side on the ride.



The third picture shows the 3 ribbon cables and 2 ethernet cables to remove. Also (not shown) there is another cable which goes to a 2x5 keyed IDC connector which has to be disconnected from the RF input board on the right.



The fourth picture shows the location of the internal cables in the display/computer module. (The green flex cable is a huge pain to remove and an even bigger pain to reconnect.) To open the module, there are only 2 screws on top, 1 on the left, and 1 on the bottom. Disconnect the cable to the hard drive, but you don't actually need to remove the hard drive.



The fifth picture shows the location of the SMD fuse circled in green. Note that on the CRTU the inverter module is actually a CXA-L0605-VJL (https://media.digikey.com/pdf/Data%20Sheets/TDK%20PDFs/CXA-L0605-VJL.pdf), not the CXA-L0605A-VJL that richnormand linked to. To test the board after replacement, apply 5V to pins 1 and 3, and ground pin 2. I used an SMD polyfuse to replace it, so hopefully I won't ever have to replace the fuse again.



And finally, the last picture shows everything working!