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Monday, 4 February 2019

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!!!)







Wednesday, 30 January 2019

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 !

Thursday, 24 January 2019

Pioneer SA-6200 - low and distorted

John called.

"Got this Pioneer amp I've bought. Not sounding too good. Can you take a look?"

Yeah, why not?

It's Pioneer SA-6200 , dating from around 1974. It's described as a medium power versatile amplifier.


Powering up and it's very distorted on the right channel.

It's obviously never been apart before. It's full of dust inside. A good sign, means it hasn't been got at!
I clean up the pots and switches as a matter of course, but the fault is certainly in the power amp.

It's the usual 70's push pull single rail arrangement. AC coupled to the speakers.

Checking some voltages, and something's very amiss on the input stage. The voltages on the input current mirror, Q1 & Q5 are very wrong.

Sure enough C1 has failed, and is almost short circuit.




So it's duly evicted. Looks like an electrolytic, doesn't it? Well, it isn't. It's made by Sanyo, and is, in fact, a tantalum capacitor. When they're of this age, they're more evil than the electrolytic!

It's rated at 0.47uF at 25V. I haven't got any, so I've substituted a 1u 63V poly. It'll out-live me. I've changed it's best mate on the other channel too. 


Talking of capacitors... most of the electrolytics on the amp are in poor shape too.. many physically leaking and crusty. Let's change them while we're in there ...


The re-capped board is fitted back in, and tested. Sounds good :) Making about 14.5 watts RMS into 8 ohms. It's supposed to be 15. Near enough after 44 years ;)

The amp is buttoned back up, and given a soak testing with a bit of Emerson, Lake and Palmer.

One interesting thing to note, is the amp has two phono inputs. One doubles up as a mic input. Both the inputs feed the RIAA equaliser, so your mic also has the RIAA EQ curve applied! Ah well...

Wednesday, 23 January 2019

Right to repair.

This is a partly political broadcast on behalf of Doz...

If you're in Europe (as I am until the end of March). This is important.

Stand up for your right to repair.

https://openrepair.org/news/towards-the-right-to-repair-in-europe/

If you're in that odd bit of the planet, where earth is ground, and the mains wobbles up and down a bit faster, but not as far as here, valves are tubes, and tubes are CRT's (I'm talking about the USA).

https://repair.org/stand-up/

We can't keep chucking this stuff away! And, repairing brings an amazing feeling of satisfaction (I know, I've been fixing things for 40 years)

Don't let this stall.

Sign the petition, and make the world a better place.


Picture stolen from Ifixit.com (who make an excellent screwdriver kit) , sorry.

***STOP PRESS***

This turned up on IFL science this morning too...

https://www.iflscience.com/chemistry/chemicals-elements-that-make-our-smartphones-are-running-out-new-endangered-list-reveals-/?fbclid=IwAR0-RaNu40VvVLq14TfMor4xJ_CK5iQOY_N1RQCG_Lkzff5I2sjniAPuQTw




Tuesday, 22 January 2019

Beocord 2000 De Luxe - no playback.

Pyers put out a distress call on the internet ..

"Does anyone have an old reel to reel which does 3-3/4 ips 1/4 track? I have a load of old tapes to digitise."

A mutual friend came back with this ..


It's a Bang and Olufsen Becord 2000 De Luxe (no less)

"Needs a service. Hamstall Ridware: But it’s bloody tidy. Dust cover and all."










It found it's way here...

Initial testing showed it only worked on one speed (there are three, 1 7/8 IPS, 3 3/4 IPS and 7 1/2 IPS), and even then only when it was tilted on it's side. It was also running slow when it was running...








Two of the world's longest screws, and the bottom comes off.

Doesn't look like it'll help us much, as the fault is obviously mechanical.















Although I can get a glimpse of what's to come!

Off with the top plate...
















It's immediately apparent that the capstan is not being driven properly. Belts look in reasonable nick though!










The spring that holds the idler against the capstan flywheel, and the motor drive hub has broken, there's precious little friction to drive the flywheel.

You'll need to remove both the rewind and capstan drive idlers to gain enough access.







The spring has broken at the hook end, so I shorten it as little as possible and form a new hook.

This is the bias oscillator. We'll need to remove this to get the spring back on. There are two screws each side of the heatsink...






And the module is carefully unplugged, and set to one side.











Then, after some not inconsiderable cussing, the spring is attached at the capstan end, fed through and attached at this little bar underneath the bias oscillator.









The capstan idler is cleaned, and slid back into place, and secured with it's circlip (not forgetting the felt pad).

It's the same procedure for the rewind idler.

The bias oscillator is replaced.








Just need to clean up that grubby tape path, and put it back together!















And it's up and running :)

Saturday, 19 January 2019

Linn Majik - humming fault

"Ho, ho, ho , It's magic you know , Never believe it's not so"

Except for this one. Magic it isn't...

It's another of Colin's Job lot of Linn stuff.

A Majik integrated amplifier.


Connecting up and switching on it works, but is humming badly from the right hand channel. 

Probably more caps I'm thinking ... let's get it in bits and have a look.

Same MO as the other Linn products in this range, four screws holding the top cover on, are found underneath. Slide off the top cover and put it to one side...
We'll need to remove the remote / balance input board from the rear panel. Two screws, and a couple of plastic support, and it lifts out. Talking of balanced audio... why oh why oh why an RJ11 socket?? XLR's not good enough? 

OK, having got that out of the way, we're going to need to remove the main PCB. Flip the unit over, and remove the 5 screws holding the heatsink to the base plate. 


Remove the screws holding the phono sockets to the back panel.

There are four screws to remove to remove the PCB from the base plate. Two by the capacitor bank, and two on the other side, marked "tool hole" and "sneaky"!

The front panel needs to come off so we can get the headphone jack to clear.

Two screws at the top, left and right...

and two underneath (the silver ones).

Disconnect the ribbon and the two pin connector to the power LED, and remove the front panel.

One the links for the power / amp amp are removed from the back panel, the main PCB easily lifts out. A cursory visual check shows nothing obvious. The main electrolytics are still in fine shape, as they're still holding charge.
Right, we're going to need to get the thing back together to begin testing... so the transformer is plugged back in, and the front panel. It's all a bit dicey. Be careful not to allow the board to short out on any of the case! There's no need to plug the balanced board back in, it'll run happily without.

Without the heatsink bolted to the base plate, it does get quite warm quite quickly, so keep running times whilst testing to a few minutes, then let it cool down.
Powering on shows all the LT rails (+/- 26V, +/-15V and +5V) are all present. The power amp is now isolated from the pre-amp, and the hum remains. So our right hand power amp is at fault.

Comparing differences, both static resistance measurements, and using the scope between left and right amplifiers under identical conditions, I can't see any difference between the amplifiers except for the output of the right amp.

I short the input of the right hand amp to ground, to see if the hum is getting in through the input somehow. It makes no difference.

It must be a fault within the output IC's (TDA1514A) of the right hand amplifier (there are two IC's per channel, in parallel). The problem is the TDA1514A is obsolete. I won't risk the eBay IC's... they're bound to be fakes.

Damn.

One thing I have noticed is there's a bit of 100Hz ripple on the -26V rail. But both amps share the same +/-26V supply (It's actually +26/-25)... so surely it can't be that, can it? I change C602 and C603 which are the local decoupling capacitors to the power amp IC's. There's slight "change" to the hum, but it's very much still present. Encouraged by this change I look at the supply.

Now the -26V supply is regulated by a 2SC3519 pass transistor which is controlled by an LM337. The adjust pin of the regulator is decoupled with a 100uF capacitor. The input is decoupled by another 100uF capacitor (C308 & C310). These two caps are right up against the tab of the regulator. They may have well been cooked by the heat. Decoupling the input to the pass transistor is yet another 100uF capacitor, C320. I change the lot. 

Shush! Can you hear it? Me neither, the hum is gone! 

So why on earth was the left hand amp not affected?? One of life's little mysteries..

Now the +26V rail has a similar set up, but uses a 2SA1386 pass transistor and an LM317 regulator. The components are mounted in a similar manner. I change that lot too, so we should have a reliable amp.

There , all playing nicely again. Another saved from landfill...




*STOP PRESS*

Steve's been in touch. He writes "The board is a Knekt receiver board and the RJ45's are for balanced audio & 2 way control from main room sources, the other socket is for the RCU (Room Control Unit) a wall pad to control the amp and local or remote sources."

Now the RJ45 makes sense!

Thanks Steve.