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Messages - Ki Choi

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Tape Tech / Re: New (to me) ST 1510A question
« on: July 08, 2011, 04:47:51 PM »
Hi Guys;

One of my ST 1510As has an issue with L channel output reference level.  It will only go up to 10mV, and most of the time, I can move the level up and down. R channel default to 1.29V at power up and it can be adjusted to 2.0V for self test mode.

Unfortunately, the service manual I had borrowed from Charles King doesn't include schematics for Output Reference boards that is not found in ST 1500A.

DocB is checking for a ST 1510A service manual but if one of you has a PDF copy I can use, please let me know.


Hi Larry:

Wouldn't it been beatiful to think the session was also recorded in direct two track R2R...?

Tape Tech / Re: STUDER A810 tape transport: problem solved!
« on: June 17, 2011, 10:17:26 PM »
Hi YJ:

I trust DocB will chime in with the answer on the Tape Project tape availability.

If your EPROM had contacted with the battery acid enough to eat into the pin, my guess is that you would need to replace the EPROM socket as well.  Before you replace the EPROM socket, I would suggest you use a little DeOxit on the pins and socket contact points.  Ultimately, it is better to replace the socket.  I had done the same to one of my A810s' MPU card.

Judging from your email address, you must be in Taiwan.  I travel to Taipei about once a year for work.  If you have the means to burn an EPROM chip, I can send you the BIN file for the IC10 via email.  Otherwise, send me your mailing address. I will put the IC10 for 2591 version in the mail to you.

The thump sound you hear as well as the VU meter jump full scale after power up initialization is common on old A810s.  It is due to some of the 5532 OPAMPs in Line Amp card needing replacing or I have also found both Rerp Amp and Line Amp card with marginal electrolytic capacitors making noise after power up.

Lastly, did you replace the two electrolytic caps in the head preamplifier located under the headstack for +/- 15V supply?


Tape Tech / Re: STUDER A810 tape transport: problem solved!
« on: June 14, 2011, 10:26:42 AM »
It is always nice to have a happy ending to any saga.  Good job, YJ.

I am impressed that you were able to find the problem without having access to the other working parts for quick swaps.  It's a good experience for you and hope you too have gained a huge appreciation for Studer's design team as I have in making the A810 so much easier to work on in comparison to other consumer machines and even the Otaris.

As long as your A810 is going through the power up routine with some counter number display first, the firmware version display (2591), VU meter lamp resets and finally locking in the capstan motor phase-lock-loop indicatior (if you have your capstan control board configured to do so - otherwise when you lift one of the tension arms or have tape loaded) without any EEEXX display, your firmware chips are healthy and good.  There's no need to look any further on the firmware checksums.

Now that you have a working machine, you need to call DocB and sign up for The Tape Project!  ;-) You won't know how good the A810 really can sound until you have threaded the Arnold's Overture tape and hit play.

Although I get wrapped up in hoarding machines but they are just one of the means to the ultimate end - good music.

Tape Tech / Re: STUDER A810's initialzation problem.
« on: June 07, 2011, 11:08:46 PM »
The Studer A810 verison 2591 firmware has the following checksum values in hex numbers:

IC10 9744
IC12 FF04
IC14 E88E

I would suggest you check the chip's labels to make sure the IC location numbers are visible.  Otherwise, mark them with pen before removing the chips from the MPU board.  Wrap them in the aluminum foil and take them to your friend with the Eprom programmer.  It will take him only few min to read the checksum values.  Let him do the reading because if you are familiar with the programmer, there's a chance you will do damage to them.

Fortunately, I have archived the firmware in BIN files.  In case any one of your chips are damaged from the PS failure, I can email you the file.

Reel to Reel Tape Machines / Re: A80 1"
« on: June 07, 2011, 05:06:23 PM »
Hi Doc:

thanks for the update.

My guess is that you will go from the original 1" master to dubbed 1" master to be played back on your 1" 2 tk A80 + Tape Repro. Guess it can't get any closer to the original than that...

OTOH, 2" 2 track... that sounds obscene...

Tape Tech / Re: STUDER A810's initialzation problem.
« on: June 07, 2011, 02:55:49 PM »
Hi YJ:

If you can borrow the Eprom programmer, you can remove your firmware chips and read their CHECKSUM values and report.  Unfortunately, I don't have the proper checksum values for 2591 chips here at work, but I will post them for you to compare tonight.  As long as the checksums are good, the firmware chips should be ok.

Without the board extender, it is nearly impossible to trouble shoot the MPU card.  Let's verify that your firmware chips are good.  If not, I can send you a set or send you the BIN files.


Tape Tech / Re: STUDER A810's initialzation problem.
« on: June 03, 2011, 04:18:39 PM »
Hi Guys:

As I had mentioned before, the 1000uF and 470uF caps on Basis board should be the first caps to replace. 

The Studer A810s are fine machine (although some of the real "pro" are not considering them as worthy as other Studers).  However, there are known issues that I had dealt with over the years again ...and again.

The choice of electrolyic cap manufacturers - both Fracko and Philips are bad...
The earlier A810s will have plastic locking tab on Input connectors that will not lock or most likely had broken off..
The ferrite sensors for tension arms that are glued in can easily come off from its plastic housing
The leaky battery that will eat away the circuit traces on MPU board...
Placement of tape splicing block that will be sured to leave razor marks on the speed control panel
Older A810s have problem with card rack cover hindges.  They are so thin, if not careful, they will bend and break off.
Oh well, I'll think of more.

Tape Tech / Re: STUDER A810's initialzation problem.
« on: June 01, 2011, 11:50:17 PM »
Hi YJ:

Glad you found the source of the short. Judging from your description of the dreaded yellow Frako caps in them but still have LED display, your A810 must have serial numbers in the 3000 range (at the youngest).  Thus, the machine is at least 30 years old...I would suggest you check other electrolytic caps in the basis board and replace them all before you go any further.

BTW, there are one big and one small electrolyic caps in the power supply as well.  You should replace them if not done already.

I normally do the cap replacements in the basis board first, then the power supply, the LED display, and two caps in the pre-preamp under the headblock that are know to fail as well.

Again, check all of your voltages under load after cap replacement.  I would check the +24VDC supply and make sure the solenoids for the brake control is working ok for your play problem.

Although you have the "2591" display at power up, you won't know for certain that all three firmware chips are ok until you check their checksum number.  However, 2591 is the latest firmware.

Tape Tech / Re: warped reels?
« on: June 01, 2011, 10:59:05 AM »
Although no metal reels are perfect, Tape Project tape reels are better than other metal reels in my experience.  Matter of fact, most of us use TP original take up reels for all tapes.

My guess is similar to what others had said above, your BR20's reel turntables might be set too low.  You can generally look with metal reels loaded and see how much clearance you have betwee the deck surface and the reel.  If you find that the gap is very small, you should use spacers or contact United for adjustments.  Revox/Studers use metal washers for the reel motor shaft and other machines are adjustable with set screws.

You should get it fixed before the metal reels start to scrape the surface of your deck cover.

Tape Tech / Re: STUDER A810's initialzation problem.
« on: June 01, 2011, 10:50:38 AM »

In addition to the partial response above, it seems the bad PS section had wiped out your firmware chip(s).  Before looking to replace the firmware chips, you should take out the MPU board and make sure there are no battery leak and should replace the battery now that you have lost all of your setup data in the RAM.

All the other transport's irratic behaviors could stem from MPU problem due to bad firmware.

It is good news though that your capstan control is live and well as long as you are getting phase lock yellow LED lit and can change speeds.

After replacing the suspect electrolytic caps, you should look at the DC supplies with an O'scope under load to make sure your PS repairs are good.

We should revisit after you had resloved the fore mentioned basic issues.


Tape Tech / Re: STUDER A810's initialzation problem.
« on: June 01, 2011, 10:43:42 AM »
I am not an expert but let me give you few comments:

After restoring all the connectors and powered up, the green LED's on meter bridge firstly lit. Then a click, but no red LED on the panel, no firmware version on display.

KC] Based on work you have done to revive the power supply section, I suspect the A810 had massive power failure mostly likely due to one of the filter caps dying on the basis board.  I would recommend you check all the electrolytic caps on the basis board and there are two 10uF caps on LED display board as well that you should replace.

I got all LED's on channel control, periphery controller light up (except one associated with "MAX"). Was it part of the initialization process which is somehow interrupted? On periphery controller the red LED "Store" was on, could it be the "write" phase to RAM triggered the interrupt?

KC] One of the constant results of PS failure especially with +5.6V problem is the three firmware chips probably are damaged.  Having no power up ruutin u
I'll have to restart my response.  sorry.
After a while the capstan seemed to respond to speed selection. There is a stable yellow LED on master control section (PLL; capstan). The red LED also would become stable after speed change.

Fast backward worked. But it can only sustain about 30 sec. or so. Then the tape lifter solenoid became erratic. (On-Off-On-Off) It seemed that the regulation of tension was failed.

"Play" function resulted in fast spinning of right spool motor. (Pressure roller had been engaged.)
At stop side near the break bands only the upper solenoid could activate.

Manually thread the tape pass the reproduction head I can hear the beautiful sound on the tape.  through monitor speakers! Probably that audio chain was still O.K.

I suspect the MP board was not function properly. Maybe the content of firmware (25/91) was corrupted?

What would be the basic reaction of an A810 with failed firmware? Will ""FF" "Stop" "Play" "Fast backward" still can be activated? ("Record" did not respond, through.) If the firmware was the culprilt where can I get the content of it?

Best Regards!

Y.-J. Wu

Tape Tech / Re: New (to me) ST 1510A question
« on: May 16, 2011, 04:59:15 PM »
It's just fine!


Say no more.... if Charles says fine.  You have a nicely working 1510A...

Reel to Reel Tape Machines / Re: What hardware are you using?
« on: May 15, 2011, 05:26:39 PM »
I am just getting started refurbishing and modifying a Technics RS 1520. Ordered a tape path upgrade kit and am sending head block #1 off to JRF this week to get it back to stock.

Eventually in a few months head block #2 will be sent to get back to stock except for a Flux Magnetics playback head to use with an Eros preamp.

Hi Tim:

Welcome and it seems you are already deep into seeking the best sound possible.
Now you need to get some Tape Project tapes to play on your modified Technics.

Reel to Reel Tape Machines / Re: What hardware are you using?
« on: May 15, 2011, 09:40:53 AM »
Forget the tape machines... but horns....Wow!

What is the small Khorn like corner horns?

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