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Author Topic: STUDER A810's initialzation problem.  (Read 14286 times)

Offline yjwu

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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

Offline Ki Choi

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Re: STUDER A810's initialzation problem.
« Reply #1 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

Ki Choi

Offline Ki Choi

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Re: STUDER A810's initialzation problem.
« Reply #2 on: June 01, 2011, 10:50:38 AM »
H YJ:

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.

Thanks,
Ki
« Last Edit: June 01, 2011, 11:00:26 AM by Ki Choi »
Ki Choi

Offline yjwu

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Re: STUDER A810's initialzation problem.
« Reply #3 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

Offline Ki Choi

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Re: STUDER A810's initialzation problem.
« Reply #4 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.
Ki Choi

Offline yjwu

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Re: STUDER A810's initialzation problem.
« Reply #5 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

Offline mrush

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Re: STUDER A810's initialzation problem.
« Reply #6 on: June 02, 2011, 10:49:51 PM »
Hi YJ:

Sounds like you are making good progress on your 810.

Try holding the stop button when you press the CCIR/NAB and Mono/Stereo buttons.  There is a dip switch on the Periphery Control board that enables the calibration mode.

The caps are definitely a problem. My 810 was built around 1987 and all the blue Philips caps are bad.  I haven't had any short yet but they all measure around 50% to 75% of the capacitance.  A few have been open.  I started with the power supply and audio boards and haven't gotten to the Basis (mother) board yet.  It's the one all the other boards plug into.

I have tried spinning the guide roller and the counter never seems to move.   It always works with tape.  Can you run any tape yet?

Thanks,
Mac
Mac Rush

Offline yjwu

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Re: STUDER A810's initialzation problem.
« Reply #7 on: June 03, 2011, 02:26:22 AM »
Hi Mac:

Thank you for your input here. Looks like we are in the same boat.
I just finished printing 28 size A3 circuit diagrams (double sided) of the A810 service manual. Better than zoom in and out and move around a pdf file.
Browing through some paragraph I also realize that the CCIR/NAB Momo/Stereo button can be actived by holding "Stop" together with individual key. The basis board refers to the mother board.
So far my counter always stay at 0.00.00. Ki's suggestion is great. I though all those 1000uF/470uF capacitors need to be replaced ASAP. Maybe it was another bad capacitor which mess up the communication bus. Wiping out those capacitors could be my weekend's job. I will get enough parts to continue.
Since I did not have any LED on before successful initialization, it is relatively easy to trace the fault on LED display board.
I could not play any tape. Sometimes the right reel spins backward in play position, some other time it spins too fast.
Tonight I will unplug the VU meter and see wheter there is correct error code. It is a proof that part of its brain is still functioning, at least.

Regards,

Y.-J. Wu

Offline Ki Choi

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Re: STUDER A810's initialzation problem.
« Reply #8 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.
Ki Choi

Offline yjwu

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Re: STUDER A810's initialzation problem.
« Reply #9 on: June 07, 2011, 12:14:53 AM »
Hi Ki:

My A810's SN is 4081. I replaced all the 1000uF, 470uF capacitors on basis boards. Not much improvement.

There is no LED until 2591 flash on. (Or "." or "PP PP" ; most of the time it was just blank) Tape counter would not responds, always stay at 0.00.00. At fast forward/rewinding I can measure square pulse on right tension board.

When I unplugged the VU meter connector there was correct error code "EEE13" on display. There is no "EEEE1/2/3" at initialization.

The "Play" was always engaged in fast rotating of reel motors. Its direction seemed to correlate with the previous "Fast forward" /"Fast rewind" position. The program can not set the correct tension at play position.

I can borrow an EPROM programmer from my friend. Maybe I should reflash my 2764 with correct program content if I can access it. But I need to collect three 2764.

The A810 can change and store audio parameters. Test generator seems to work - there is reading on VU meters, but not through monitor speaker. 10dB botton works as expected. Channel control can be set to be locked together or change independently.

CCIR/NAB MONO/STEREO switches work as expected. Capstan motor can be phase locked. It can also be set to rotate at all time or be turned on when there is tape.

Input amplifier works as expect, with VU meter.
 

Thank you for your sharing.

Best Regards,

Y.-J. Wu

Offline Ki Choi

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Re: STUDER A810's initialzation problem.
« Reply #10 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.

Ki
Ki Choi

Offline yjwu

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Re: STUDER A810's initialzation problem.
« Reply #11 on: June 07, 2011, 06:32:57 PM »
Hi Ki:

I will contact my friend for the EPROM programmer. Then I will report the checksum value.

Thank you!

Best Regards,

Y.-J. Wu

Offline Ki Choi

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Re: STUDER A810's initialzation problem.
« Reply #12 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.
« Last Edit: June 07, 2011, 11:15:22 PM by Ki Choi »
Ki Choi

Offline yjwu

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Re: STUDER A810's initialzation problem.
« Reply #13 on: June 08, 2011, 09:23:50 PM »
Hello Ki:

Those three EPROM's were clearly marked as IC10, 12, 14 with their part number on a foil by felt-tip pen. The previous owner was VOA. Battery was changed to Ni-MH type(probably in 1993?). No leak. It was charged to 3.6V.

Thank you!

Y.-J. Wu