My poor old CDU150 (amongst other things)

[G8VAT Wolfman]

Having recently started a new job, I'm no longer working in IT and back to my roots in electronics servicing, this means I have access to some modern test gear.

Having several outstanding major problems at home I borrowed the digital scope for this weekend, so far so good...

First to come under scrutiny was our Wharfedale Freeview HD/DVD recorder, it's been dead for a month or so but we tend to watch it only for DVDs or to record to DVDs, this didn't actually need the Scope as one look at the PSU showed many bulged caps.. so a quick blitz with what I had on the shelf and a shopping list sent to Farnells and it lives again (noisy bleedin fan and all).

18 screws later the TV was under my gaze, this has had a very bad patterning on all analogue inputs for ages and more recently the digital/processor side has started crashing, more suspect caps.. I have alreday blitzed the PSU PCB (and blown it last year).
But this time I can study all the surface mount caps on the main PCB with the scope and many of them show an amount of fuzz on the lines they are supposed to be smoothing, two of the 12v lines have nearly half a volt of rubbish, but.. putting another cap across does little if anything to improve it, I am getting a sinking feeling.
However I tot up the caps where noise is noticably present and double it then another list added to the Farnell basket..

Whilst I'm on a roll, I went and retrieved my poor old Cossor CDU150 scope from the fusty end of the garage. as a result of the dampness in there this had said, 'Bang!' about three years ago and not been touched since, it had shown 50Hz lumps on the trace for quite a while before that too.
A good long search turned up nothing in the way of the full service manual that I have for the Scope so I had to start with my eyes..
A couple fuses later and I had to start using my ears as I was greeted by an EHT arcing at switch on and I had to simply move one of the EHT caps away from the chassis to quieten things, so at this point I'm now back to pre bang.
Looking around and checking supplies to the Y amps showed plenty of 50Hz, I eventually found the main smoothing bombs underneath, I doubly checked that this (flimsy looking) digital scope is fit for high voltages and point the probe at the caps, just as the probe touches there was an almighty bang as my wife opened the bathroom window and the door immediately behind me was closed by the sudden wind..
I took a walk round.
Back to the caps, and yep there was loads of rubbish on the supplies, one cap had the tell tale bleb in the rubber endcap just to prove it's guilt.
Whilst studying the PSU I noticed one of the ZTX transistors had a gaping hole in the casing, it checked OK however and looking at all that style of transistor shows they all have a moulding mark in that position so I think it is simply that..

All done before dinner, I'm not so impressed with modern technology, the digital scope seems flimsy and difficult to see, that old LCD viewing angle problem, the trace just doesn't have an accurate or fast feeling about it, but in fairness it was man enough for what I threw at it, I'll be glad to get the old CDU back tho.

[G8VAT Wolfman]

SO finally to my question.. does anyone have or know where I can get

3x 500+50uF @200v dustbins and
1x 2000uF @25v

Also does anyone know what this is all about?
There is a fuse holder inside the EHT area, it has two 560k resistors to ground and the live side goes to the PSU PCB, there never has been a fuse in there..

[Stockden]

Originally Posted by G8VAT Wolfman

Also does anyone know what this is all about?
There is a fuse holder inside the EHT area, it has two 560k resistors to ground and the live side goes to the PSU PCB, there never has been a fuse in there..

It doesn't feed the probe sockets on the front panel dies it? That's the only thing I can think of that would leave the scope working when a fuse is missing.

Oh and I have a copy of the manual in PDF (actually 3 files totalling about 18Mb!). If you'd like a copy send me a PM with your email address.

Hugh

[KeithsTV]

I have some 330uF 200v caps which you're welcome to have for the cost of postage.

PM me if interested

Keith

[chip-chop]

" ... There is a fuse holder inside the EHT area, it has two 560k resistors to ground and the live side goes to the PSU PCB, there never has been a fuse in there .. "

I seem to remember, years ago, some "industrial" type kit would be fitted with what looked like a 1¼" fuse but was actually a time elapsed indicator, to show how many hours use the item had been subjected to.

Just a thought??

[Stockden]

".. There is a fuse holder inside the EHT area, it has two 560k resistors to ground and the live side goes to the PSU PCB, there never has been a fuse in there .. "

Well, I've had a bimble through the manual and I can't find anything that matches what you describe. Indeed I can't see a 560K resistor on any of the component lists (that's not to say there isn't one of course, just that I couldn't see one!). Can you post a picture and I'll see if I can match it with any of the diagrams?

Hugh

[WME_bill]

Very intrigueing. I have looked at my CDU150 awaiting attention, and see nothing like what you mention. As a picture is worth many words, I attach photos and PCB layouts of the Rear Assembly, the Power Supply 'A' and the EHT generator 'B'. Also the circuits of the boards 'A' and 'B'. Could you identify what and where this fuseholder assembly is located.
The circuits diagrams are to the usual Cossor drawing standards, and are extraordinarily awkward to follow. The handbook was a genuine original copy, and marked 'Issue 2'. I also have one marked 'Preliminary Issue',which appears identical.
What you find may spur me on to put mine onto the bench for repair. Bill m0wpn

[G8VAT Wolfman]

I did actually upload a pic of the item but it got lost somewhere.. am at work but I'll judt do this then have to get back to you all a bit later, cheers Gra...

[Sideband]

Just an idle thought....is it for discharging the EHT? Short the 'fuseholder' across with a crock clip lead (earthy end applied first) and the scope switched off.......

There would be enough clearance between the fuseholder caps to prevent flashover.




SB

[Stockden]

Fascinating, it's clearly not present in Bill's CDU150 and I don't recall anything like that in the one I used to have. It seems that you have something unique!

By look of it it's a professional "mod" rather than an amateur addition. Somewhere I have parts of the EMER for the CDU150. I'll see if there are any modification instructions amongst it that sheds any light on the matter.

Hugh

[G8VAT Wolfman]

well another possibility there, I think the Elapsed Hours Timer is probably the most likely, I have seen those in other equpiment (including VCRs) and I can see how that would work, the one thing I should do is check the voltage on the 'live' end of the fuseholder which goes onto the rectifier PSU PCB.

It does look like it has been added later, not an original fitment.

Thanks for the offers of the Caps and the PDF Manual, I might take you both up on those a little later if all else fails, I have a full manual somewhere in a box from our house move about 5 years ago..

[G8VAT Wolfman]

Here is yesterdays body count, this isn't by any means all the caps on the main PCB, I concentrated on those around the Logic array, but I'm pleased to report that the heavy patterning and crashing have gone.. or should I say returned to the level of when the set was new..

[Sideband]

Always hated those surface mounted electrolytics. Wherever possible I used standard electrolytics as replacements, carefully cutting and shaping the leads so they would fit the original solder pads.


SB

[G8VAT Wolfman]

I hate them too now.

[Stockden]

Well, it looks as though Clive is right - it was for an elapsed time indicator.

I dug the EMER out today and Modification Instruction index has, at instruction number 14 (dated Feb 73), "Provision and fitting of elapsed time indicator". Unfortunately the instruction itself is missing, so I can't actually confirm that it involves adding the parts you've identified.

There is, however, a "Miscellaneous Instruction" dated Dec 80 describing "Removal of elapsed time indicator". All this is does is state that the item poses a hazard if it gets broken and instruct that it is to be removed, placed into "Bottle, Screw Cap, Polythene, Type 60" and sent to COD Donnington in an appropriately marked package.

So all that would account both for the fact that your scope has extra bits that aren't mentioned in the Cossor manual and that the fuse-holder is now empty. By the look of it these things contained some very nasty chemicals so it's probably a good thing that the holder is empty!

Hugh

[m0cemdave]

Originally Posted by Stockden

So all that would account both for the fact that your scope has extra bits that aren't mentioned in the Cossor manual and that the fuse-holder is now empty. By the look of it these things contained some very nasty chemicals so it's probably a good thing that the holder is empty!

Only Mercury, which as a hazardous substance has to be disposed of properly.
This is an electrolytic elapsed time indicator in the same size package as a 1-1/4" fuse. It looks like a miniature thermometer, with a transparent liquid bubble that gradually moves from one end of the mercury column to the other.
Here's a picture:
www.spamabyss.net/pictures/Hrcounterpic.jpg

[Stockden]

Originally Posted by m0cemdave

Only Mercury, which as a hazardous substance has to be disposed of properly.

I'm very happy to defer to your greater knowledge, though the wording in the 4 paragraphs of hazard warning suggest that there may also be something else. To start with it refers to "chemicals" (plural) though that may just be loose language. Perhaps more significantly it says:

Spillages should be cleaned up with wet wipes and the resultant contaminated paper incinerated immediately, not being allowed to dry out. It is emphasised that the wipes must not be allowed to dry out lest they self ignite whilst stored awaiting incineration. Alternatively a non drying stable liquid such as glycerol should be used as a wetting agent.

Clearly it's not metallic mercury, so it's presumably a compound of mercury in solution with something that's liable to self ignite.

Hugh

[dave cox]

http://www.google.co.uk/search?sourc...w=1292&bih=685

[dave cox]

See attached pdf...

[Jason Pero]

SMD electrolytics is suspect except for colored marking like red, blue or purple which are polymer capacitors which is much advanced and reliable.

I did shotgun many SMD electrolytics in toshiba rear projector hyper modules long ago. And still usually check for any degradation when I come across these SMD caps.

Cheers.