The Studer A-820 is a good machine...
The transport is killer, the audio electronics well designed
and overall it's perhaps the one of the best machines Studer ever built.
I DO prefer the A-827 over the A-820.
Note that Studer does NOT support the A-820 Studer does not sell any A-820 parts anymore
In theory you may be able to obtain A-820 parts from
AudioHouse in Switzerland.
Here are some helpful tips I've found over the past years working on Studer A-820 machines...
First off, just like the A-827, there are a number of EPROMs inside the machine, and these
can and will go bad - causing a complete machine failure.
Somehow, there was a flaw in the Studer 'self-test' programming, so if one
of the EMPROMs fails, the 'self-test' can go through it's entire cycle
and finish up telling you that the machine is in perfect condition - even
though you can't get the transport to do anything....
So if this happens to you, it' most likely one of the EPROMs, just order them from Studer
and replace all of them... if you're lucky that will solve the problem.
Personally, if I owned a A-820, I'd buy a new set of EMPROMs right away
if the machine is older than 6 years old and just replace them now.
Make a back-up set of your machine's EPROMs...
Next you need to make sure the machine's RAM back-up battery is current and good.
If that battery goes bad, ALL of your stored alignments will be lost and the machine will totally revert to the factory settings for all tape deck
settings (tensions, and so on) and well as ALL audio settings.
Next I gotta tell you that I'm seeing a lot of A-827 and A-820 machines
with power supplies that are now malfunctioning. All the power
supplies in these machines are 'switching' power supplies, meaning they are EXTREEMLY
DIFFICULT to repair. I've had to repair 4 power supplies in the last 6 months,
and these are pretty dang new machines. Often the failures are due to the Owners
leaving the machines on for 24 hours a day.... causing the caps to go bad, transistors and FETs
to fail, the MOSFETs to blow up... and so on...
If you own a A-827 or a A-820 DO NOT LEAVE THEM 'ON' 24 hours a day !!!
Next you want to make sure that you do NOT set the wind or play tensions too high...
use the basic specs for tension given in the manual and have the tensions checked
once in a while. Tensions set too high can force the machine into oscillation in the wind modes
Make sure you WRITE down the tensions settings in the manual!! Engineers WILL change
the tension settings and they will not mention it to you... I've seen this happen too many times.
From time to time lift the transport up and remove the connectors one at a time,
spray clean the sockets and press the connectors firmly back into their sockets....
(of course with the machine turned off !!!)
Then after all the connectors have been cleaned,
you MUST test ALL the audio and transport functions!!!
by the way I use "LPS-1 Greesless Lubricant" as my spray-cleaner of choice
Next you need to learn the 'feel' of the transport control buttons -
they have a tendency to go bad now and then, and you need to know when one is about to fail...
there should be a good solid 'click' to the button, and it should bounce back after being pressed.
Note that the A-820 is a micro-processor controlled machine....
it's basically a computer, but it's getting OLD... it's a 15 year old computer now,
and chips do fail, EPROMs loose their memory, and strange things can start to happen.
Make a list of the various chips in the control system, and make sure that
you have a couple chips of each kind sitting around... some you may find hard to find,
but it's better to try and find them now, then when the machine's not working...
some chips will take hours of searching to find, but do it now!!
Various components in the A-820 are now getting old - the power supply caps, the
specialized caps in the Switching Power Supplies, and so on...
Heat over the years is also destroying such items as the tops on the Adjustable coils
in the Capstan Tach Card, which may just fall off if you even touch them... so
you really need to be careful with everything you do in a A-820.
Note that Studer does NOT support the A-820 in any way anymore -
no Parts, no support, no anything....
Also note that the cost of Studer heads is very high - too high for most studios
to afford to replace heads once they're gone....
so make sure that the tape lifters are pushing the tape away from the heads in wind modes!!
Remember that in the 'auto-mute' mode, you will NOT hear the repro system in the fast-wind modes....
meaning that if the lifters were allowing the tape to touch the heads, you would never hear it !!!
So physically check the lifters, or undo the 'auto-mute' and listen in the wind modes.
Finally..... I never use the Auto-Alignment in the A-820.
I always align the machine track by track.