On 3/21/11 6:29 PM, "Jules Richardson" <jules.richardson99 at gmail.com> wrote: Several years ago the scrapper I was working for got a couple pallets of "dead" plasma monitors and TVs. None of them would power on, and none of them had any status LEDs visible... We opened a tv and monitor up and first bloody thing I did was hook up a power cable and take a meter to the output of the power filter/socket assembly. -0- Volts AC.... Bypass it and voila the monitor lights up... Check the TV and the same damn thing.... All of the monitors and tvs had the same problem. $30 each later and they had a LOT of plasma monitors and TVs to sell.

It is normal to replace the enbtire assembly, and it's quite likely that a suitable replacement can be obtained. Of courde you might want to have a go at repairing it. Whether this is possible depends on what has failed and if you can get inside the module. If it is a normal filter assembly, it will contain a bifilar-wound inductor (which is almost impossible to obtain as a 'loose' component) and 3 or more capacitors (which are avialable. There may be aschematic on the can. If you get continuity from the liv/neutral pins to the tags to whci hthe itnernal wires are connected, then the inductor is probably OK. Most of the time if there are problems it's one of the capacitor that has failed I suspect some of thse modules are filled with 'potting compound' (a mad friend of mine clals this 'potting compost' :-)) which makes repairs almost impossibel. Some DEC machines have a filter in a square metal can about 6cm on a side on the back of the inptu conenctor, the lid is soldered on. I think you van probably desodler the lid with a _large_ solderign iron and repari it. The type that looks like deep IEC socket behidd the panel is probably not repariable. -tony

It's not pointless if : You want to keep the machine as oriignal as possible by replcing the smallest part necessary ( for example a capaciotr rather than the complete module) It's one of the 20% or so you can't get easily. and you don't want to make any modifications to the machine to use an alternative You enjoy fixing thigns rather than replacing them. Rmember I routinely repairr cooling fans to component level. I've repaired switches and light bulbs too :-) I assume this is one of the modules with voltage selector contacts? Is it one of the ones with a little PCB under the fuse that fits several ways round? Or one of the ones with a plastic camshaft you cna fit in sevearl orientations? Or what? I've found that the filter units on those tend to come apart fairly easily -- they're not potted and the metal can is easy to unsolder. You cna then repair/replace the filter. Well, provided it;s not USB :-) (Sorry, couldn't resist) -tony

Samll incandescent filament bulbs. I thought I'd mentioend this before. It was a bulb with a difficult-to-find cap, so I broke the old glass (containing the burnt-out filamanet) out of the cap, cleaned up the latter, and soldered a wire-ended bulb of the right rating to it. Given that it was useless anyway, I think I would have tried cutting the end off the filter section. You migth have been able to extract the defective components and wire in standard filter module (thus keeoign the votlage selector feature of the original). I have come across these units on some HP devices. The Thinkjet printer and the HP9817 computer spring to mind. There are several versions of the camshaft, one just operates one of the contacts fopr 115V/230V switching of an SMPSU, the other operates all the contacts for configuring a 0-120 and 0-100-120 priamry mains transformer for 100V, 120V, 220V and 240V. The Thinkjet does that, and the service manual doesn't explain it (the one on my shelf has an extra sheet in it now giving the wiring..) -tony

And that looks like a very standard typoe of IEC320 plug with a built-in mains filter. It';s also a design that I've never tried to open to repair, because it's so common. The parameters that matter are the maximum voltage that the capacitors in the filter will stand (but I wouild be suprised if any wouldn't take 240V mains), and the maximum current that the inductor in the filter can carry. The latter should be more than the fuse rating in the device. But I can't believe DELNO takes that much current, so most filters will be OK. I would think so. -tony

If a properly-funcitoning DELNI draws anyhting like 10A from the mains, I will eat one :-). I am sure it would be fine. And if it isn';t, a file will take care of the problem :-) As for the wiring, the ground (earth) lead will go to a tag that it conencted to the metal casing, it's normally the centre tag. The other2 tags ar, of course, live (hot) nd neutral. It probably doens't matter which way round you conenct them, but in every similar mains filter I've used, the output tags are directly behind the corresponding plug pins, so it's easy to work out which is live and which is neutral. They may even be marked o nthe filter can. I don;t know what wiring colourse are used in the DELNI. It's likely to be either : Black : Live White : Neutral Green : Earth or Brown : Live Blue : Neutral Green/Yellow : Earth. -tony

I have now dione what I should have done ages ago amnd looked at the DELNI printset on bitsavers (under dec/ethernet IIRC) [1]. I find that the printset is always the best manual to look at first :-) [1] As you all know by now, looking at on-line documentation is rather more work for me than for most people, which is why I didn't instnatly look at bitsavcers to see if there was anything useful. Anyway, I was somewhat suprised by the PSU. It's not an SMPSU. At least one of the regulators looks to be a switching type,, but the power supply starts with a mains transformer (running at 50Hz or 60Hz). The primary windings of that transformer go to the nromal series/parallel switch and then to the mains input. Oh yes, there's a fuse in series with the live wire. Now, 10A, even at 110V is over 1kW. a 1kW (more correctly 1kVA) trransformer is a big lump of iron. I doubt one would fit in the DELNI case. So I am sure a 10A filter will be fine. When you replace it, make sure that the wire that goes to one end of the fuseholder goes to the live output tag on the filter. It's very clear [Modifying the case] Well, agreed, I'd rather mont have to do it, but it's better to slightly enlarge the hole than have a non-working device, isn't it? I think it will, these things come in fairly standard sizes. Admittedly it was just an IEC320 plug, not one with a built-in filter, but I found a generic plug from the local electroncis shop was a perfect fit as a replacement for a broken one in an HP9820 calcluator made over 25 years earlier. No cutting, filing or drilling needed. SInce when have pliers been a substitue for a spanner??? Darn it, I don't even like using adjustable spanners if I can avoid it. Incidentally, I find I need 3 sets of spanners to work on classic computer stuff : Inch size (to fit USA built stuff mostly). And I need odd sizes like 11/32" sometimes. Metric sizes (needed on just about anything modern-ish, and everything European). BA sizes. BA is a strange thread used mostly on older British stuff. You need BA spanners to work on Creed teleprinters, for example. AAnd yes, open-end, ring (box end?) and nutdrivers are all useful. -tony

Assumingyou can easily read .pdf files, look at the printset on bitsavers. You don;t ahve to undersntad the logic, the mains transfotmer is easy to spot. It shows the primary side wiring, which is what yuu are working on. BA nuts ans bolts are still commonly used by model engineers over here, amazingly. And they do turn up on electrical stuff, when I bought some barrier strips recently, I found I could get such thins with M3.5, 6-32UNC or 4BA terminal screws. Anyway, BS fasteners are not common in classic computer stuff, but you will find them in old British stuff. Creeds being the most common place, but otehr things too. I suspect old GPO modems, for example, use them (the telephones certainly do). -tony

Excellent!. I am not suprised it was the right size to drop straight in. Sounds like the pwoer supply is doing something (LED on). From glansing at the printset, the logic doens't seen all that complicated, and should eb repairable if necessary. -tony

I think the first thing you need to do with that one is to find out what the output voltages should be _and which pins they're on_ so you can see just what it is, or is not, doing. A 'tweeting' PSU is generaly one that is trying to start up, detecting a problem, and then hutting down again, Possibly due to bad capcitors (often, but not always, on the output side. Maybe an overvoltage problem (so the crowbar circuit is tripping). Possibly a problem with the shutdown circuitry itslef (there isn't really a problem, but the shutdown is being triggered anyway) -- but whateveryou do, don't be tempted to disable protection circuits. I did once, when younger and more foolish, and ended up with transistors blown apart, metled track, and many other things to repair. I've yet to fidn a really good book,web page on this. The way I learnt was to read the scheamtics and circuit descriptions of every docuemtned PSU I could find, to read all the data shets on the control ICs, etc. It is very difficult in my experience to repair an SMPSU without a schematic. You may be lucky and spot the bad component, but most of the time you need to work through the schematic logically. Alas the scheamtics of most modern-ish PSUs are unobtainable. I gnerally resort to tracing out the full schematic, then interpretting it, and only then starting to fix the thing. -tony

You are correct, of course. The actually IEC 320 spec (or whatever it's called now -- EN60320, perhaps) is not cheap. I think I discovered that to gert the whole thing would coat around \pounds1000 and (a) I don't have that sort of money and (b) if I did, I'd have better things to spend it on. However, when I was writing about the HP9800s, I did try to track down thge correct names for these connectors. As far as I can see IEC320 C14 is the chassis-mouting input plug used on most eleectrical equipment. IEC320 C13 is trhe cable mounting socket o nthe end of the mains lead It appears to be incrrect to call the chassis socket (like the one on an IBM 5150 PSU to plug the 5151 monitor into) a C13. The best reference I could find called those : IEC 320-2-2 Sheet F for the chassis socket (power outlet) and IEC 320-2-2 Sheet E for the cable plug (as on the end of the 5151 monitor mains lead). -tony

I suspect it has, actually. I also believe you can see the BSI standards (but not make photocopies, althpguh you can make handwritten notes) at the place near Kew Bridge in London. I've never tried it, though. Interesting. I will look into this. Indeed. I still feel that standards docuemnts should be 'cost of reprodcution' only. Obviously they cna't be public domain (there has to be a restrictuion on distributing modified versions or there'd be terrible cnfusuion), But alas they're not, and are IMHO ridiculously expensive for what they are. -tony