Studer A807

carlosraj

New Member
Oct 22, 2017
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#1
Hi

I am new to this forum. A friend of mine brought this reel to reel to get it fixed. The problem was, the fuses keep blowing. When I first ON the tape player there was no lights on any indicator and the VU meter was dead. Upon opening, I realise that 3 fuses, the +15V, -15V and +50V have blown. I replaced them and turned ON the player again. I realised that both the VU meters have swinged to the maximum (fully clockwise) and the +6db,+9db and +12db red indicators are on, no output and the tape deck 'STOP" indicator flashing. I OFF and ON back the player and the same results. When I OFF and ON the third time , the fuses blown again. Can someone assist by advising me what could have gone wrong or where should I start troubleshooting.

Thanks

Carlos
 

Ki Choi

Member Sponsor
May 13, 2010
740
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16
Seattle WA area
#2
Hi

I am new to this forum. A friend of mine brought this reel to reel to get it fixed. The problem was, the fuses keep blowing. When I first ON the tape player there was no lights on any indicator and the VU meter was dead. Upon opening, I realise that 3 fuses, the +15V, -15V and +50V have blown. I replaced them and turned ON the player again. I realised that both the VU meters have swinged to the maximum (fully clockwise) and the +6db,+9db and +12db red indicators are on, no output and the tape deck 'STOP" indicator flashing. I OFF and ON back the player and the same results. When I OFF and ON the third time , the fuses blown again. Can someone assist by advising me what could have gone wrong or where should I start troubleshooting.

Thanks

Carlos
Carlos

Unfortunately, it isn't as easy to pin point the cause of the fuse blows. I would not replace anymore fuses and power up the sick machine again until you have located the sources of the problems. The +/- 15V fuses and +50V fuses are blowing more than like due to faulty electrolytic capacitors downstream from the fuses. I would suggest you track down the problem one step at a time.

+/- 15V are for audio section and more critically +50V is for your Spooling Motor Control and Capstan control boards. I would suggest you focus on +50V problem first. There are two major area of known problems with these machines. if you have a A807 Mk I, it is more likely you will have problem with the stud mount can type electrolytic capacitors C1 through C4. C1 charging capacitor is for +50V. By unsoldering either the black or red wires on the cap terminal, you can test the health of the cap with a capacitor meter. Or just replace all four of them. They are the dreaded Frako made and will eventually fail. Once you have done the C1 repair/replacement, you can move on to the other areas of problems.

Both the Spooling Motor control board and the Capstan Control board are known to have the smaller Frako capacitors, C23, C24 in Spooling Motor control and C65 in Capstan Control boards fail all of them at 220uF 63V. If your A807 is not MkII and if the axial capacitors in the Spooling Motor Filter board - that is attached to the Spooling Motor Control Board - are not blue Phillips type, I would replace them while you have the board assembly out. they are 6 ea 100uF and 6 ea. 47 uF at 60V axial electrolytic capacitors.

After you have made the repair on both Spooling Motor Control Board and Capstan Control board, you can disconnect the red and black wires (after marking their position) from both boards and then replace the T4A fuse for +50V supply. You can now power up and if the C1 is good, the T4A fuse will not blow and you should be able measure +50V between black (-) and red (+) supply for Spooling Motor Control. If you get +50V, then power the machine off, reconnect the red and black wire on just the Spooling control board (leave the red and black wires on Capstan board unconnected for now). If the C23, C24 and Spooling MTR filer caps are all good, Spooling Motor Control board should work well.

Next you can measure the red and black wires on Capstan board and you should get -50VDC. If the C65 is replaced, Capstan should be working. You can reconnect the supply voltage wires with machine off. You can turn the power on, manually move up the tension roller by hand, and hit Play. Both spooling motors should spin as well as the Capstan will turn.

there are other possibilities of one of the semiconductor such as diodes or transistors going bad but it's rare.

It's a same process of troubleshooting for Audio section to repair for the +/-15V supplies. Hope it helps. Ki
 

carlosraj

New Member
Oct 22, 2017
14
0
0
#3
Carlos

Unfortunately, it isn't as easy to pin point the cause of the fuse blows. I would not replace anymore fuses and power up the sick machine again until you have located the sources of the problems. The +/- 15V fuses and +50V fuses are blowing more than like due to faulty electrolytic capacitors downstream from the fuses. I would suggest you track down the problem one step at a time.

+/- 15V are for audio section and more critically +50V is for your Spooling Motor Control and Capstan control boards. I would suggest you focus on +50V problem first. There are two major area of known problems with these machines. if you have a A807 Mk I, it is more likely you will have problem with the stud mount can type electrolytic capacitors C1 through C4. C1 charging capacitor is for +50V. By unsoldering either the black or red wires on the cap terminal, you can test the health of the cap with a capacitor meter. Or just replace all four of them. They are the dreaded Frako made and will eventually fail. Once you have done the C1 repair/replacement, you can move on to the other areas of problems.

Both the Spooling Motor control board and the Capstan Control board are known to have the smaller Frako capacitors, C23, C24 in Spooling Motor control and C65 in Capstan Control boards fail all of them at 220uF 63V. If your A807 is not MkII and if the axial capacitors in the Spooling Motor Filter board - that is attached to the Spooling Motor Control Board - are not blue Phillips type, I would replace them while you have the board assembly out. they are 6 ea 100uF and 6 ea. 47 uF at 60V axial electrolytic capacitors.

After you have made the repair on both Spooling Motor Control Board and Capstan Control board, you can disconnect the red and black wires (after marking their position) from both boards and then replace the T4A fuse for +50V supply. You can now power up and if the C1 is good, the T4A fuse will not blow and you should be able measure +50V between black (-) and red (+) supply for Spooling Motor Control. If you get +50V, then power the machine off, reconnect the red and black wire on just the Spooling control board (leave the red and black wires on Capstan board unconnected for now). If the C23, C24 and Spooling MTR filer caps are all good, Spooling Motor Control board should work well.

Next you can measure the red and black wires on Capstan board and you should get -50VDC. If the C65 is replaced, Capstan should be working. You can reconnect the supply voltage wires with machine off. You can turn the power on, manually move up the tension roller by hand, and hit Play. Both spooling motors should spin as well as the Capstan will turn.

there are other possibilities of one of the semiconductor such as diodes or transistors going bad but it's rare.

It's a same process of troubleshooting for Audio section to repair for the +/-15V supplies. Hope it helps. Ki


Thanks Ki Choi, the 50V fuse stop blowing after sometime, but the +15V and -15V keep blowing constantly. I opened out the power supply board and checked all the bridge rectifiers. Both the +15V and -15V bridge rectifiers had shorted. After replacing the diodes, now it is working normal. My friend told me that prior to this problem, recording was the problem and ask me to try the recording. I was not too sure of the recording procedure and these is what he told me to do. Connect the L and R line-out (RCA) from the CD player to the L and R XLR connectors line-in of the tape player. Press the "Ready" and "Input" buttons on top of the VU meters for both channels. Then press the "Line On" and "Uncal" buttons below the VU meters for both channels. Set the tape counter to "0". Both the "Ready" LEDs were flashing. Adjust the L and R "Line Level" pots so that the VU meters point to 0db. Then press both the "Play" and "Rec" buttons together to start recording. I did as told and re-winded back the tape to listen to the recording. I pressed the "sync" buttons on top of the Tape player for both channels and press "Play". Only then I realised what my friend was trying to tell me. The play back was very, very soft and I can see that the VU meters are hardly moving. During recording the volume was very very much louder and the VU meters were readily moving across the 0db level. What do you think can be the problem. Can it be the recording bias or the preamplifier or tape head. Appreciate your advice on this.

Thanks again

Carlos
 

Ki Choi

Member Sponsor
May 13, 2010
740
0
16
Seattle WA area
#4
Carlos

Do you have a copy of the A807 service manual? You should get one online and study machine calibration section. Although +50V T4A fuse is not blowing, it blew before for a reason. I would suspect you still have marginal capacitors in Spooling Motor Control Board or the Capstan Control Board or both. If you plan to use the machine for a while, I would recommend you check into it.
 

carlosraj

New Member
Oct 22, 2017
14
0
0
#5
Carlos

Do you have a copy of the A807 service manual? You should get one online and study machine calibration section. Although +50V T4A fuse is not blowing, it blew before for a reason. I would suspect you still have marginal capacitors in Spooling Motor Control Board or the Capstan Control Board or both. If you plan to use the machine for a while, I would recommend you check into it.

Yes, I downloaded online. I will check all the capacitors on the two control boards as suggested. I am wondering whether the problem can be with the calibration as according to my friend , the recording was normal previously and he did not meddle with any calibration controls. Anyway I will study the calibration section and do accordingly.

Thanks

Carlos
 

Ki Choi

Member Sponsor
May 13, 2010
740
0
16
Seattle WA area
#6
When you lost +/- 15V, there might have been damage done to your audio section. Without feeding signal and tracing changes in amplitudes, it would be difficult to say. If there were any damages done to audio section, you won't be able to calibrate and get proper results within Studer spec.
 

carlosraj

New Member
Oct 22, 2017
14
0
0
#7
When you lost +/- 15V, there might have been damage done to your audio section. Without feeding signal and tracing changes in amplitudes, it would be difficult to say. If there were any damages done to audio section, you won't be able to calibrate and get proper results within Studer spec.
Thanks Ki Choi. This morning while trying to calibrate the machine in accordance to the manual, I had another problem. The tape started playing as normal, then it started to slow down and eventually stop dead. I pressed "play" again but the tape tension lever and the pinch roller doesn't engage. Finally I decided to open up the capstan control and spooling motor control boards. The resistors, transistors and diodes seem OK. I then stripped off all the electrolyte capacitors from both board and started checking. I just could not believe that all the caps have dropped drastically by 70% to 80% and some almost dead. I then decided to check both the audio and microprocessor boards. The result is the same. I called up my friend and told him that I have decided to replace ALL the caps on the machine. I hope this would solve the recording and the motor spooling problem.

Carlos
 
Jan 18, 2012
547
0
0
Drobak Norway
#9
on my A80s I replaced all electrolytics and tants on all boards incl counter,motion sensor, logics and audio
also all bearings in tape path
and motor caps
"litttle use" doesn´t help, they all dry out
best
Leif
 
May 30, 2010
13,917
7
38
Portugal
#10
on my A80s I replaced all electrolytics and tants on all boards incl counter,motion sensor, logics and audio
also all bearings in tape path
and motor caps
"litttle use" doesn´t help, they all dry out
best
Leif
Just a quick note. Most A80 boards have solid aluminum capacitors that do not degrade over time and do not need replacement. They look like tantalum capacitors, but they are not. Some people say that replacing them with tanatalum's will compromise the original design. But there is some divergence on the subject.
 

Ki Choi

Member Sponsor
May 13, 2010
740
0
16
Seattle WA area
#11
Just a quick note. Most A80 boards have solid aluminum capacitors that do not degrade over time and do not need replacement. They look like tantalum capacitors, but they are not. Some people say that replacing them with tanatalum's will compromise the original design. But there is some divergence on the subject.
Agree. They are organic type as I recall.
 

carlosraj

New Member
Oct 22, 2017
14
0
0
#13
Hi,

Now I have replaced all the caps on the machine. And now I face another problem. The rewind and fast forward works normal, but when I press "play", the tape plays at a fast speed, then slows down, fast again and then slows down again and eventually stops. What I mean is that the speed is inconsistent. Can it be due to the tape tension
arm. Thinking that the pressure roller that locks on to the capstan is loose, I tried pressing it tight on to the capstan, but that makes the speed even faster. I really need your expertise and guidance here. Please help.

Thanks

Carlos
 

carlosraj

New Member
Oct 22, 2017
14
0
0
#15
sounds like you need to learn how set up brakes, tape tension, pinch roller pressure etc
get a manual if you don´t already have one...
Hi

Setting the tape tension, as according to the manual. Connect meter to TP2(ground) and TP5(+) on the "spooling motor control PCB". Hold the right tape pancake and press FAST FORWARD. I get a reading of 10.02V on my DMM (should read 10.0V according to manual). Next connect meter to TP2(ground) and TP1(+) on the "tape tension sensor PCB". It is stated "Press tape tension sensor to the rear until distance "X" (see figure) is 85mm, then adjust to 0.0V using trimmer pot R16(10K).
I am not sure of this instruction, the distance between the tape tension lever and the sensor coil behind it is only approx 3mm, how do I press it in to the rear to a distance of 85mm. I guessed what it meant was to push the lever upwards towards the left reel (not sure) to a distance of 85mm . I did that but could not get a reading of 0.0V by adjusting trimmer pot 16. As I keep tuning , the voltage goes down to approx 0.3V and then suddenly it goes into millivolts (not able to get 0.0V). The other adjustment is to release the tape tension sensor to its rest position and adjust to 4.0V using trimmer pot R11(500K). This I am able to adjust to 4.0V exactly. After this adjustments, I pressed "play". It starts to play normal, but at certain points especially towards the end, the left side reel starts to make some squeeking and grinding sounds. In FAST REWIND mode, it starts to slow down towards the end. Is this due to misalignment of the tape tension. I do not have a 'TAPE TENSION METER" and not able to set the mechanical spring tension between the left reel and the tape tension arm.

Thanks

Carlos