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Topics - yjwu

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Hello STUDER experts:

Recently my STUDER A820 developed a problem which prevented it from FF/rewinding/library winding; soon after the command was issued an error message INCORRECT RADIUS MEASUREMENT appeared briefly; then tape tension dropped, tape unloaded. According to the manual the culprit would be tacho sensors (Spooling motor?). Although I do not have an extender board 1.820.799.00, I managed to soldered wires from six resistors after pin 1~4, 7,8 on TD Couter/timer board 1.820.761.82, which represents two 90 degrees out ot phase-50% duty cycle square wave from left/right tacho sensors of left/right spooling motors and the motion sensor. The duty cycle of each of six square wave signal was measured/adjusted by monitoring it through a scope.
Problem persists.
Other aspests of the tape handling of this A820 seemed to be O.K.

Currently configuration:

SM-DRV: 820.759.84
CAP-CTR: 820.764.28
CAP-IF: 820.727.00
TD-PER: 820.762.81
TD-C/T: 820.761.82
SM-CTR: 820.760.82
TD-MPU: 820.785.26
TD-S IF: 820.763.83
M-S IF: 820.753.82
M-MPU: 820.786.33
M-PER: 820.728.81

Firmware: Master MPU: 1.820.996.32: 02/93; TD-MPU: 1.820.995.24; 35/95; Capstan Control: 1.820.994.27; 10/92

After firmware update this A820 operated half a year without any problem.

+/- 15V, +24V: negligible ripple with no specific pattern;

+5.6V: 40mVpp, ~100Hz ripple;

+/-26V: 200mV/400mV, ~30Hz ripple spike;

POS: measured +45V, 1.5Vpp, ~100Hz ripple
NEG: measured -48V, 1.5Vpp, ~100Hz ripple
CAP/AUX: measured +48V, 100mV, ~100Hz ripple; POS/NEG/CAP-AUX ripple are saw-toothed shape.

Yes, this machine encountered many abnormalities recently. First MOVE SENSOR HARDWARE; was diagnosed to be a faulty 74HC14 on TD counter/timer board; followed by a faulty SRAM on master MPU board, which rendered A820 unbootable. This INCORRECT RADIUS MEASUREMENT seemed to follow all the way through. Finally I got some time to look into the 50% duty TD-TMR1/2, TD-TML1/2, TD-MOVE1/2, hoping the problem would be cured; but it was not that simple.

Maybe it is time to replace the main filter capacitors in main power supply.


Any suggestion?

Yeun-Jung Wu

2
Hello:

Recently I restored a non-functioning STUDER A820. Now it works beautifully!

Its software configuration was as followed:

1) master MPU (820.786.21): 1.820.996.20                             : 38/86
2) capstan controller (820.764.26): 1.820.994.25                    : 35/88
3) tape deck MPU (820.785.21): 1.39.88 (?)                             :???         hard to decipered hand writing

According to STUDER list the most up to date hardware and software for A820 Mk-I was

Capstan:1.820.764.28       1.820.994.27                                  10/92
Tape Deck:1.820.785.26    1.820.995.24                                  35/95
Master MK: 1.820.786.24   1.820.996.22                                  06/89

Does STUDER's ftp site provide enought information for hardware/software upgrade to most up to date version?

How about the difference between Mk-I and Mk-II? I know the skimming and HX-Pro was inplemented on Mk-II. Is it possible to migrate from Mk-I to Mk-II?

yjwu

3
Tape Tech / STUDER A810 tape transport: problem solved!
« on: June 13, 2011, 07:21:07 PM »
Dear Reel to reel experts:

After replacing five RC4559N's on reel motor control board, my STUDER A810 starts playing music!! (I had not found which of these IC's were fault yet. Listen this A810 singing is a much more joyful moment!

I would like to thank Ki Choi for sharing experience in pinpoint the problems. Followed his suggestion
I replaced most of the electrolytic capacitors on basis board, and many more. It will extend the life of this A810 for another period. He also suggested me to review the checksum value of the firmware chips. Before I call my friend for help I did the  IC swapping. Surprisingly problem had been solved! Maybe those chips are still O.K. I will defer the check until audio/mechanical line up are done.

Thank you for taking time viewing my post. I want to thank Mac for sharing his experience of fixing his A810.

Wish we all have healthy A810 to enjoy. Let the legend continue forever!

Best Regards,

Y.-J. Wu

4
Tape Tech / STUDER A810's initialzation problem.
« on: June 01, 2011, 01:28:07 AM »
Dear reel-to-reel experts:

Recently I fixed a partially carbonized power supply board of a troubled A810 (sold as a part machine). Replaced one burn TRIAC (Q11, BT136 -> BTA12), one short capacitor (C14), one melt capacitor (C5) I got 24V, 6.5V and +-15V back to work!

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.

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?

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

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