great video it always a pleasure to watch someone who knows what there talking about, thanks for the tip with the diodes

@michaeldranfield7140

6 ай бұрын

No problem , many thanks for watching .

Another excellent video, thank you for sharing it with us. Why can't the three diodes be replaced with just one diode (of suitable size) to solve the issue of having three diodes in parallel?

@MichaelBeeny

6 ай бұрын

Don't be silly, that would make sense!

@michaeldranfield7140

6 ай бұрын

That's a good question , because this is only the stand by power section which draws very little current anyway, some people think its planned built in obsolescence

@glpilpi6209

6 ай бұрын

I wondered that too. It doesn't look very old either and it's popped a cap already. I'm not used to newer equipment doing this. Although I had a popped cap. in a repair I did for a friend who had a Wharfedale computer amp which can't have been more than a few years old with a major hum , they were all cheap 85 deg. C electrolytics. Nice job and good vid. as always Michael.

@michaeldranfield7140

2 ай бұрын

@@glpilpi6209 not designed to last , its all about selling a new one these days .

The guide board provides an insulator for electrical equipment safety. On the primary side of the SMP (switch-mode power) supply the AC mains is full-wave rectified to around 400V. The ribbon cable to the display panel sits over the SMP. The creepage and clearance distance requirements reduce through solid insulation. There also appears to be a foil shield on the ribbon cable to reduce electromagnetic disturbance. This should align with the metal section on the guide board thereby providing a path to ground.

Always knew you were into heavy metal! Great video! 👌

@michaeldranfield7140

6 ай бұрын

I'm not actually , I have always been punk but I do like heavy metal .

Great detective work there Michael, well done

@michaeldranfield7140

6 ай бұрын

Done 2 of these now with same fault so it looks to be a common problem .

@Meepsmusic63

6 ай бұрын

@@michaeldranfield7140 yes, i picked that up from ya video Michael, and shocking on the state of play on those cindering leds on ya latest samsung tv video, i should be replying to that there but i always get things backwards lol, Huge respect for your knowledge and skills and passion and ability Michael

@michaeldranfield7140

6 ай бұрын

Shocking the Samsung TV , this is the millennium not the 70 s when it was common place for a TV to burn up.@@Meepsmusic63

Nice one sir. I've just picked one of these up cheap off ebay - sold as faulty. I was only googling to see how to get the damn bottom cover off and there was your video and yep, exactly the same fault. Dead short on one of those diodes. I got myself a nice little amp for my den now.

@michaeldranfield7140

Ай бұрын

Many thanks for that , glad it has helped you .

It's a shame Panasonic don't use Panasonic capacitors in their own equipment (sound bars in particular). Good repair!

@michaeldranfield7140

2 ай бұрын

Too expensive now and at the end of the day manufacture's don't want things lasting for years , its all about selling a new one now .

Great video Michael.

@michaeldranfield7140

6 ай бұрын

Many thanks for watching .

The music made me chuckle 😅

@michaeldranfield7140

6 ай бұрын

not a fan of quality music then ! I'm into punk but don't mind heavy metal and I had to find something royalty free so I don't get a strike .

@AndyDoz

6 ай бұрын

@@michaeldranfield7140 it just surprised me a bit. I love a bit of Rammstein when I've got a difficult problem to solve!

excellent video agree abot diodes connected in parallel

@michaeldranfield7140

6 ай бұрын

At least it didn't cause any more damage , just like the vestel TV sets , a quick easy job .

I have had very bad experiences with SK parts, especially ones supposedly "original" part numbers. Bought some " SK exact replacement number" HO xistors that blew out in a day in a Sony TV Distributor swore they were 'exact prime parts". . Ordered original part numbers from a different supplier, and never a problem. Sent parts back to dist for money back. Really annoying. I believe the xistors were out of spec or counterfeit ones. Sony TV's are very fussy on specs.

@michaeldranfield7140

6 ай бұрын

so much fake stuff around these days its difficult to buy proper parts only last week I had a fake part from a big distributor that I had to get a refund for , they tried to tell me it was a genuine Toshiba supplied transistor and initially refused a refund until I offered to send it to Toshiba for a second opinion at which point they suddenly changed there mind , gave me a refund and said they didn't want the part returning , so they new it was a fake all along .

Thank you for the video, regarding the components on the underside I got caught out with that with a pcb for a welding machine, looked easy to repair until I removed it and seen all the ICs underneath

@michaeldranfield7140

6 ай бұрын

Quite a few times I have looked at something and thought that looks easy , until you turn the board over like you say.

I've always thought Denon was good HiFi but not so sure looking at that. As for that music??? was it music?? If my amplifier made that noise, it would be on the bench for repair.t

@sw6188

6 ай бұрын

Denon have dropped in quality, like most electronics manufacturers. That power supply certainly isn't made by DENON. It will be a generic china made unit that is sold to different end manufacturers and used in various models of amp. If you want good gear, look at the stuff made in the 80s and 90s before the cost-cutting started. That applies in the most part to any manufacturer.

@michaeldranfield7140

6 ай бұрын

Personally I don't think good audio is surface mounted , its not the music I usually listen to , I have always been punk but I don't mind heavy metal .

Was that Deaf Snake, or White Leopard, or something? Yeah, those rotten little diodes that consign many a telly to the skip. I remember my eldest niece had a Vestel made "Panasonic" that failed in its warranty period. The engineer's report stated that it was PSU fault, and that he'd replaced three diodes and two electrolytic capacitors. Thing was, I told her what the report said, before she even red it, ans was she miffed when I pointed that it was an economy brand wrapped in Panasonic plastics and flashed with Panasonic software! What a pity they couldn't have added those resistors............

@michaeldranfield7140

6 ай бұрын

I just typed in royalty free heavy metal music on youtube , you get a strike for not using royalty free music , the diodes on vestel are a good money maker , I must admit I have always liked vestell stuff right back from there CRT days .

Sounds like a bit of lottery in terms of how closely the three diodes characteristics match, and I doubt they're actually measured and binned into sets for manufacture. I just bought a used PMA-60 (apparently well looked after and not used at high volume) rather than a new one (a few still available) because I'd heard there was a problem with units dying after a few months or year or two and figured one that's survived a few years would actually be a safer bet. ETA >> that said, I'm now concerned enough that I might pre-emptively order a spare PSU board while they're still available (assuming it uses a similar design to the PMA-30 - I'm definitely going to open it up and take a look).

@michaeldranfield7140

5 ай бұрын

If this is something you are thinking of keeping a spare board would be a good idea as I find these things soon go no longer available , and a spare would also be very useful for fault finding .

The problem with putting silicon diodes in parallel is that the temperature coefficient of the forward voltage drop is negative. As a result the diode with the lowest Vf gets hotter resulting in it hogging even more current. What I don’t have in my head is whether Schottky junctions are the same. That’s why I like MOSFETS their temperature coefficient is positive so they play nicely in parallel.

@d614gakadoug9

6 ай бұрын

Paralleling diodes in separate packages is always somewhat perilous. What is very common and something I've done in many SMPS designs is paralleling two diodes that are in the same package. Because of good initial match and temperature tracking that works well.

Thanks Michael maybe that guide is some kind of heat shield or interference shield as there is a transformer and mosfet underneath 😊

@michaeldranfield7140

6 ай бұрын

More likely some sort of RF shield as you say .

@wisher21uk

6 ай бұрын

@@michaeldranfield7140 seems like it

Hi mate no soft soak balls out with metal or punk and you've never changed hahaha ROCK ON !!!!!

@michaeldranfield7140

6 ай бұрын

No , still punk after more than 40 years , I quite like heavy metal also though.

Nice repair but the music sounded like roadworks

@michaeldranfield7140

6 ай бұрын

Just what my mate who doesn't like proper music says !

i say an accounted has been designing a power supply

@michaeldranfield7140

6 ай бұрын

Same as everything these days unfortunately, paying more no longer buys better quality.

Fixed a Dell monitor by removing one of a pair of parallel Zeners. Never did replace it.

@michaeldranfield7140

6 ай бұрын

I bet you could just take out the faulty diode and it would work fine until one of the others failed , its only the 5 volt stand by rail so current drawn is very little .

@jms019

6 ай бұрын

@@michaeldranfield7140 That’s exactly what I did using only side cutters. Never replaced the diode. This particular monitor was a cast-off from the university then the museum.

Parallel diodes are fine as long as the Vf is matched, usually from the same batch. The voltage rating may have been borderline with that snubber.

@michaeldranfield7140

6 ай бұрын

diodes are only truly matched when there on the same die such as the 3 terminal double diodes, I would guess these diodes prob originated in China where quality control is very variable .

@d614gakadoug9

6 ай бұрын

That is a tiny snubber and primarily there to reduce RFI. Unless the design is very strange, 60 V diodes for a 5 V output of a flyback converter, even with "universal input" are more than adequate. There can be a penalty of higher forward voltage with higher reverse voltage rating in Schottky and some ultra-fast recovery PN diodes, so arbitrarily putting in higher voltage parts is not a good idea.

Switchmode power supplies are very efficient and seem great until they blow up. I worked on these for over 20 years at a power supp[ly manufacturer and I can tell you they are not very reliable unless properly designed and built with top tier parts. When questionable parts are used they are just firecrackers waiting for someone to light their fuse.

@michaeldranfield7140

6 ай бұрын

I think these days everything's built with sub standard parts , I have never seen anything built with good quality capacitors for well over 10 years now .

I prefer my old denon. Linear power supply and class ab amp. Although an stk. Whats with all the complicated class d and switch mode.

@jasejj

6 ай бұрын

Size, weight, cost. Quality no longer features.

@Tegelane5

6 ай бұрын

Denon still makes oldskool class AB amplifiers with ordinary transformer (like Denon PMA-600)

@michaeldranfield7140

6 ай бұрын

Too right anything vintage is made with quality components not to mention much simpler circuitry.

I guess if it'll play heavy metal music it'll play any thing ! Is it just me or is it usually the middle diode that fails in the Vestel power supplies ?

@michaeldranfield7140

6 ай бұрын

That's what my mate says that doesn't like proper music ! It is the middle diode that usually fails in Vestel TVs , very odd.

Denon back in the 80's had a top tier reputation for quality - Look at them now. Cheap chinese cr*p

@jasejj

6 ай бұрын

​@@willywonkawhitecaneman Denon were never British.

@jasejj

6 ай бұрын

Yeah unfortunately like so many respected Japanese companies they became uncompetitive in the 2000s thinks to Chinese competition, and the brand was bought up by one of these American-based brand peddlers who trade on these companies' former good names and get stuff cheaply assembled in China. To be fair though they're one of the less crappy ones! It pains me to see what they've done to the like of Akai and Nakamichi...

@sw6188

6 ай бұрын

I've seen this happen with many brands, DENON included. The race to the bottom to try to stay competitive. This power supply board that Michael has repaired isn't even made by DENON. It will be a generic mass produced china job, likely sold to various manufacturers and used in a wide range of models of equipment.

@michaeldranfield7140

6 ай бұрын

true , and to me proper audio is not surface mounted .

@sw6188

6 ай бұрын

@@michaeldranfield7140 Yes, surface mount usually means budget when it comes to audio.

All you need is a power supply that is same size or smaller that supplies the same voltages, probably +5, +12 and find a way to bolt it in.

@michaeldranfield7140

6 ай бұрын

you would need the ability to switch off the main amplifier rail though when in stand by.

@cranegantry868

6 ай бұрын

@@michaeldranfield7140 Correct and that would be a bit awkward to do. You did a nice job of fault-finding in that SMPS.

Ive got an old bmw micheal with the mileometer screen not working. Is this something you could possibly fix? Ribbon cable maybe? Im in harpur.

@michaeldranfield7140

6 ай бұрын

I can take a look if you want to disassemble it first and bring it it so I can see the cable but from previous experience one one of my own cars its more likely to be the lcd display and finding a new one wont be easy .

@user-uc5vr8le7y

6 ай бұрын

@michaeldranfield7140 i can certainly do that. I know your in the buxton area as my mot guy mentioned you. Are you based up harpur industrial estate?

@michaeldranfield7140

2 ай бұрын

@@user-uc5vr8le7y Yes , unit 32 . SK17-9JL

Another sample of poor design and useing underated components. We shouldn't complain realy as it keeps us in a job. Despite the 50 plus years i have been repairing consumer electronics the same weak spots still exist, this has to be deliberate to make people buy new items.

@michaeldranfield7140

6 ай бұрын

I know what you mean , 20 odd years in the past stuff would be full of Panasonic capacitors that lasted forever , now everything is full of chineese caps and components some of which only just get past the warranty period before they fail .

@Barbarapape

6 ай бұрын

Today's gear is definately designed to fail, and for some brands there is no back up which neans we have to scour the internet looking for spares, problem is that what is avaialble are either of poor quality or fakes. It makes me laugh and annoyed when i hear the words "The Right to Repair"@@michaeldranfield7140