dbx 160x Compressor - humming and farting.

The famous George called - he's moving studios and could I be on hand to lift some things into a van.

Yeah - why not?

I'll tell you why not - one of the things was a Hammond organ. It weighed more than a small elephant. Three slightly unfit middle-aged blokes and one very fit middle aged bloke just about managed to lug it onto the van. There was a considerable amount of puffing and blowing and cussing! (blatant plug here for The Above Average Weight Band)

Anyway... George had a few duff things for me to look at too, some headphones, a few leads, and a dbx compressor. "It sort of hums and farts" ...



It's a dbx 160X, still in production today, and considered to be a bit of a classic...











The humming is bound to be a power supply problem, and sure enough one of the smoothing capacitors has a bulged top ....















... and a rotten leg. We'll change all four. The unit also has a rather unpleasant case of "glue rot". The glue has changed from a yellow colour to a dark brown. When this happens the stuff can start to conduct.









It's essential to scrape this off to prevent it eating away at the copper tracks, and causing unexpected operation due to the falling resistance of the glue!










There's some rot under the capacitor. I'm not sure whether this is due to the glue or the leakage of electrolyte...










Either way, it's cleaned up and a small coat of lacquer applied before replacing the four 470uF, 35V capacitors with 105 deg types...

Should be good for another few years service now!

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.

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 ....

Linn Kairn - no remote

Problems, problems...

The Linn Kairn I did recently came bouncing back .... (Click here for the original article)

"The remote doesn't work"...

In my defence, I didn't try the remote... and I didn't know the unit's whole history.

It was part of a Linn multi-room set up.

I checked that U7 and U10 on the user menu were set to zero... they were.

So , out with the front panel again ...

And remove the front panel PCB...

This is the area of the board responsible for the infra-red receiver... it's a band pass filter to remove any noise from the carrier, amplify it and pass it to the microprocessor for decoding.

It's fed by an infra-red photo-diode on the other side of the board ....




..... except for it's missing!! Someone has un-ceremoniously snipped it out!

Swear words were duly ordered, along with a replacement diode.









Which provided (unsurprisingly) a complete cure!

(Cathode of the diode goes to the "square" hole by-the-way... like I'm ever going to need this info again!!!)

Vintage Storacall answering machine.

The mother-in-law popped round. She's been clearing out the attic.

"Is this of any interest to you?"

Yeah , why not ...

It's an old answering machine. It weighs a lot!

It's an amazing machine... on quite a few levels...

It's "logic" control is performed using the bunch of relays you see on the left hand side.

The outgoing message is stored on a 60 second endless loop tape in the centre of the machine. The incoming messages are stored on the reel-to-reel tape on the right hand side.



The quality of construction is absolutely superb. This must have been expensive back in the day!

So expensive it was leased or hired perhaps?













Even has the original GPO 4 pole jack!













This is the outgoing endless loop mechanism. It's much the same as any other endless loop 1/4" tape mechanism. It has three tracks selectable by using the announcement switch on the tape head cover. This physically moves the head up and down the tape.

The interesting part is the end detector. This is the bit of the machine which is used to detect the start/end of the tape, so once the announcement has played out, it stops the outgoing message and starts the incoming message recorder.

Normally in and endless loop system, there's a piece of silver conducting tape, which shorts out two contacts. Not here...







There's a microswitch with a lever on...













And a corresponding slot in the tape...











And when the lever falls into the slot, it switches over .... Look carefully at the gif!










The incoming message recorder also uses 1/4" tape. Again, quality here is impressive. Proper constant speed, capstan drive.

















The end of tape is detected in the (more) traditional silver conductive tape and contacts method.

After the caller has hung up, the tape just stops and gets ready for the next incoming call.







When you get home, the machine rewinds to the start of the tape and plays the messages back.

Here's the inside of the machine. Fantastic quality Japanese construction. Early to mid 70's at a guess.. 

Here's another amazing bit ...

(You need to look past the wiring a bit) ... the entire machine is driven from one DC motor! It sits on top of the plate on the left hand side of the picture. Through a somewhat over-complicated system of idlers, operated by a solenoid (top right) , the drive is transferred from outgoing to incoming mechanisms as required.

There's one belt, which supplies the drive in rewind to the incoming message.


Yet another amazing bit ...

Despite being retired to the attic sometime in 1979 (40 years ago at the time of writing), I performed a few cursory checks, and threw caution to the wind and plugged it in. It worked. Just like that. Zero repairs required other than to clean the tape path.

Still more amazing bits...

How did I know it was retired in 1979? There were still incoming messages on it! My mother-in-law managed to date the messages!

The audio quality of these messages is superb. I know it's only a telephone answering machine, but even after sitting there for 40 years, the clarity and fidelity of the recording was superb. Sadly, due to the personal nature of these messages, I can't upload them here for you, but take my word for it!




One final thing... Storacall looks like they still exist in some form or other, still recording phone calls! I'll drop them a line !