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Messages - yjwu

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16
Tape Tech / Re: STUDER A810's initialzation problem.
« on: June 02, 2011, 07:18:19 PM »
Hi Ki:
Thank you for taking time replying my question. I did replace the blue capacitor (2200uF, Philips) on the power supply board. Its positive side bulged out and inner foils were completely burn. On that board the TRIAC for 6.5V was also severely damaged, which resulted in the carbonization of circuit board.
For basis board you mean the board with all the connectors for logic and audio "cards"?
Yesterday I checked the reel motor control board. Although I saw a slight trace of black on the flat cable, the major components (darlington transistors, diodes, other transistors) seem to be O.K. Three 0.47uF capacitors also test O.K.
One thing puzzles me is why the tape counter remain at 0.00.00, no matter how the tape guide roller spin?
When I pressed those programmable keys there were display "H.XX.XX" "L.XX.XX" "L.XX.XX" "L.XX.XX"; (calibration parameters?).
Press play and record together did not invoke record function. The red LED above Record never light up.
In master control section the tape speed control and PLL capstan work as expected. But CCIR/NAB, MONO/STEREO has no effect. On periphery control board no LED light up.
I did not have time to go to service manual in detail yet. Browing through sections I had an impression that I have to re-do the mechanical alignment again first. I disassembled both reel motors, both tension boards with rollers, pinch roller assembly, capstan rotor/shaft, tape lifter to reduce weight during transport. (Fit in a large suitcase as a luggage, still overweight a little.) I have not work with a reel machine with tension control on both sides before. Now I realize it is all a different story.
On 2/25 of service manual there is a section for error message: EE E1,2,3 for data error in one of the EPROMs. Could it be a checksum routine? I will disconnect the VU meter plug to see whether the corresponding error code appears.
Later.
Best Regards,

Y.-J. Wu

17
Tape Tech / Re: STUDER A810's initialzation problem.
« on: June 01, 2011, 08:33:06 PM »
Hello Ki:

It is great to be able to hear from you directly.

Yesterday night I revisited the MP board and could not locate any apparent errors other than firmware failure.
So I re-direct my thinking: where is the power to the LED display?

I took out the command keyboard and the LED display section. Before I dig out the little LED board I found one resistor seemed to be abused. Yes! It was a 1 Ohm current limiting resistor. There are two FRAKO 1000uF, 6V (Yes, 6V!!!!???) capacitors on the board. I found that one of them are SHORT! That explains most of the initialization problem. This short capacitor pull the 5V to low and burn 1 Ohm current limiting resistor. The resistor was used as a "fuse". So no power to the display board, probably also to CPU, etc....

After replacing these two components my A810 start initialize and "2591" had shown on the display!!! VU meter back to normal. The rest of the problem remain the same.

The power failure, which result in large section of copper foil vaporize, circuit board carbonize, is so horrible that there is a slightly blacken trace on some of the flat cables(connect pin to 6.5V?). If I did not locate
this short capacitor my newly restored power supply will fail soon. I suspect there are still more FRACO's on the road. Other damaged components? It reflects the fact that healthy power supply is the key. Conservative design to shut down circuit at over-voltage surge is also important.

Right now the play function still result in fast spinning of right reel motor. No response from tape counter. Capstan motor stop rotating from time to time. But at least my A810 still keep its memory intact. It knew its identification as an "A810"! The problem has been localized.

The war is not over yet. But at this moment I want to tank you for your helpful hint.
Next go to the tension probelm.

Best Regards!

Y.-J. Wu

18
Tape Tech / Re: warped reels?
« on: June 01, 2011, 01:38:58 AM »
I guess the original message is that the tape is not centered on the middle between two flanges. It could be the reel taible height is different. Ideally both reel tables should be set to a correction height so that the tape will not touch any side of the reel.

If I remembered correctly on ReVox A77 this height can be adjusted by inserting thin flat washers under the break drums.

Y.-J. Wu

19
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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