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Tuesday, 26 March 2019

Acer AL1716 monitor repair.

Finishing off the McIntosh last night, and I glanced up at the CCTV monitor on my workshop wall... it's flickering horribly.. I switched it off.

So I walk into the workshop tonight, armed with a new HDD for the computer, as the old one simply hasn't got a big enough swap partition to render my new video (spoiler alert, it's a TV restoration...), switch on the monitor and it just sits there, ticking slightly with it's power LED flashing in sympathy.

Hmm... the power supply's tripping.

I get it down off the wall .... It's an Acer AL1716 17" 4:3 monitor I was given secondhand 10+ years ago. It's served well.








Undo the two screws on the back behind the controls, and remove the back with a guitar pick or spudger...

Remove that bit of yellow tape, and the silver screening tape. Leave it stuck to the LCD panel, and remove the lead to the front panel controls. Remove the four screws holding the electronics to the back of the LCD panel.



Remove the four connectors to the back light, two at the top, two at the bottom...








Lift the electronics a little, and remove the connector to the LCD panel by pushing the small catches on each side of the connector, and gently removing...

Put the LCD panel safely to one side.















Remove the black plastic cover, and all the screws from both controller and power supply board. Remove the two "bail lock" screws from the VGA connector.










Now you can remove the PCBs, and unplug the power supply form the controller board.

The main reservoir capacitor was holding a good charge of about ~90V. I discharged it through a 10K resistor, so it couldn't bite!

Let's play a game of "spot the duff capacitor"



Plenty to start with!

Including this one, whose top was fine, but had let go at the bottom! I decided to change all the red coloured electrolytics.
 

The repaired PCB, and the guilty parties!



Bingo, another saved from landfill...


Now to change this hard drive!

McIntosh MC2125 and C28 conversion to 240V and replacement volume control.

Colin's mate Ian got in touch

"Got a McIntosh power amp and pre-amp, both need converting to 240V, and the pre-amp needs the volume control changing. Can you have a look?"

Yeah, why not....

The stuff duly arrived, delivered by a delivery driver who was somewhat out of breath. When I picked up the package with the power amp in, I knew why....


It weighs a lot... enough to have it's own gravity and bend light around it, which makes photography rather tricky ;) It's an odd design that has output transformers, despite being fully transistorised. Must have seemed like a good idea at the time! (or did they just miss the memo?!?!)

McIntosh had provided a nice wiring diagram of the transformer. The two primaries should be in parallel for 120V operation....














... off with the bottom, and indeed the primaries are wired as we thought. The wiring is on the tag strips in the bottom left. All that's needed is to disconnect the Black/Red lead, the Black/white lead and connect them together. The join is soldered and heat-shrinked.





The unit is gently powered up via the variac whilst monitoring the 60V rail just in case, and everything checks out ... good. On to the pre-amp...



The C28 pre-amplifier is also a bit of a beast, weighing as much as most normal power amplifiers! 

Nice block diagram on the top cover...


... and under the cover the power transformer once again has a nice wiring diagram...

So off with the bottom, locate the wiring ...  


... and modify as before :)

Once again it's powered up via the variac to check for any mistakes. It's fine.
Now, the volume control. Ian had supplied a new pot. It's also got a mains switch on it. 

It's the top right control on the front panel. Sure enough the left channel track is open about half way along.
Knobs off ... 

 Front panel removed and put somewhere safe (it's glass) 
... and finally the top panel eased up to allow (tight) access... There's a few cable clips to undo to get it this far...

After much cussing at the sharp metal edges, and a slightly different shaped pot supplied to the original one fitting, the new pot and switch are finally fitted... 

... and (thankfully) works well, giving an impressively low THD.

Sunday, 24 March 2019

Panasonic DMR-EZ27 Repair.

Skinny sent me a message on Facebook....

"Mum's DVD recorder has gone wrong. Can you take a look?"

Yeah, why not...


It's a rather nice Panasonic unit. I like Panasonic stuff. This one has failed completely dead...


Off with the lid, and the fault is immediately obvious... (or so I thought)

C1401 has had enough and blown his top... he smooths the 5V rail. In this case it's 1,200uF at 6.3V. I didn't have one, so I fitted a 1,500uF, 16V part...

Watch out for the charge remaining on the main reservoir capacitor.

Plugging the unit back in..... and .... nothing :( It looks like the power supply isn't starting up. A quick check of the capacitor in the current stimulation supply in the primary shows it's in bad shape. It's a 68uF 35V part. It's ESR was over 30 Ohms. I fitted a 68uF 63V part and tried again.

Bingo!

Another saved from landfill!
The guilty parties ....