Sansui Frequently asked, and more...

RJ, be real careful about opening a can of worms here. From your discription the problem may not be serious enough to risk making it worse by fooling with the dolby board.

The meters being off may be an adjustment. There is a procedure in the service manual to center them. If you are not using your 9090DB to add Dolby noise reduction to a tape recordings, the meter function is not critical. There are no Dolby FM broadcasts so that position of the switch is pretty much useless.

If you have normal, consistant stereo operation, and you don't use the Dolby function for recording tape, I wouldn't mess with the dolby board.

- Pete
 
Pete, I hear what your saying. I have made the db adjustment on my other unit. It was only off a little, and both meters were reading the same. Since this unit the meters aren't reading the same, .2 vs 3, i thought the meter adjustment was not in order. I have rarely used the db function for recording, since I still haven't transfered all my reel to reel tapes to cassette. Now none of cars have cassette.

The only time I would be using the db function is to bring up quality of recorded tape, while rerecording it, since the some of the tapes are begining develop problems, especially the Sony, out of 24, 7 are going bad, 7 I haven't played yet. Maxell out 51 I have only 1 bad one, (it was back coated), Scotch 1 bad. I think I have 50 more tapes to go through before I start recording, the bad ones, going through an equalizer and using db. It might be a project that will never get done, like the cassette.

Bob
 
Only the cassettes have db, the reel to reels don't. The problem tapes are all r to r, Sony tape's are PR-150, normal bias. How serious is the problem in the db circuit, with .2 L, 3 R. Does it require a complete rebuild, some part replacements, or just an adjustment as suggested earlier.

Thanks,
Bob
 
As Pete states there is a complete adjustment of the Dolby system in the service manual. According to the user manual here is how the Dolby circuit is to be used.
(We are assuming the unit is calibrated)


Select record 1 or 2, and press the tone push button.

At the recorded set the record level to 0DB

Record a short period of the tone generated (about 30 seconds).

Press the tone push button and record the source.


When playing back, set the output listening to the tone at the beginning of the tape, to 0DB.

At the receiver set the Dolby control to play, and set the level to the center of the Dolby meters.

The system is now set to properly decode the Dolby encoded tapes.

These instructions are paraphrased, I will scan and post the instructions that are in the manual in another post.
 
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Manual

As Pete states there is a complete adjustment of the Dolby system in the service manual. According to the user manual here is how the Dolby circuit is to be used.
(We are assuming the unit is calibrated)


Select record 1 or 2, and press the tone push button.

At the recorded set the record level to 0DB

Record a short period of the tone generated (about 30 seconds).

Press the tone push button and record the source.


When playing back, set the output listening to the tone at the beginning of the tape, to 0DB.

At the receiver set the Dolby control to play, and set the level to the center of the Dolby meters.

The system is now set to properly decode the Dolby encoded tapes.

These instructions are paraphrased, I will scan and post the instructions that are in the manual in another post.


Jim,

Thanks, I have the Operators manual and service manual, so no need to scan them. I have a question on the adjustment procedure. I will post that later since I am away from the service manual at the moment.

Thanks,
Bob
 
The Service Manual I have is D60720M. Referring to page 7 Section 4-1-2 Calibration Tone Volume & Dobly Meter Volume Adjustment.

1. Speaker Selection A
2. Master Volume Minimum
3. Balance Volume Center
4. Accessory Switch Off
a) Question What is the Accessory Switch, I am assuming that the Function Switch is not set to Aux Input, but is it set to, I think FM Auto.
5. Dolby Selector Switch REC 1
 
Last question

Step
1. Turn on the Dolby REC CAL TONE Switch.

2. Connect VTVM to the front Tape 1 REC terminal.
a. Question There is no Front Tape 1 REC on the outside of the receiver, I am assuming it is on the Dolby board, and the diagram that I have is not a clear copy where the terminal is on the board.

3. Adjust VR601 on the circuit board F-2655 to obtain 270mV on the indication of the VTVM.
4. Adjust both VR03 (L-CH) and VR04 (R-CH) on the circuit board, so that indicator of the power meter will be center of the Dolby mark.


Thanks
Bob
 
This thread has been a fascinating read, and a good example of what makes this board such a special place.

It also makes me more grateful than ever before, that my 9090 does NOT have the "DB" letters tacked on the end! :D Nothing in a regular 9090 is nearly as challenging as that Dolby stuff looks! :no:
 
Measurements not making sense

Use the Tape 1 jacks on the back of the receiver.

- Pete

Pete,

Set VTMV to AC on Left got 266mv, Right got 299mv Dolby Meters Left .2 Right 3. Did not adjust VR601, since the voltage was in the middle of the 270mv setting required. Is there any max not to exceed. Which to you adjust too, Left or Right?,

Checked two other 9090db's got: A) Left 290mv, Right 288mv, Dolby Meters centered at 5. B) Left 188mv, Right 186mv, Dolby Meters at 4 . Refering to my friend's units, does the variance between the Left & Right 33mv on my unit cause the problem of difference .2db left, 3db Right on the Dolby Meters?

Bob
 
Would it be to much trouble to get a scan of the manual regarding the section on Calibrating the Dolby level from anyone who has it. I've got a stand alone Advent Dolby encoder/decoder, and I want to fix it up, but I have no information on how use these outboard decoders. This would probably help as I can't find sqwat about mine.
Thanks Mike
 
Dolby Calibration

Here ya go:

9090db_Dolby{1}.jpg

9090db_Dolby{2}.jpg


Paul
 
Pete,

Set VTMV to AC on Left got 266mv, Right got 299mv Dolby Meters Left .2 Right 3. Did not adjust VR601, since the voltage was in the middle of the 270mv setting required. Is there any max not to exceed. Which to you adjust too, Left or Right?,
To get them both the same, you need to do the input level adjustment first. These values are not super critical. Just get them close.

Checked two other 9090db's got: A) Left 290mv, Right 288mv, Dolby Meters centered at 5. B) Left 188mv, Right 186mv, Dolby Meters at 4 . Refering to my friend's units, does the variance between the Left & Right 33mv on my unit cause the problem of difference .2db left, 3db Right on the Dolby Meters?
Did you adjust the meter centers with VR03 and 04? If not, give it a try. There are holes in the dolby board to access the back side of these trimmer pots. They are covered with a little piece of cloth so you have to kind of deflower them before making the adjustment.

- Pete
 
Another thing to check is the output of the tuner power supply. It powers the dolby board and meter functions. The output of the power supply is often high which can make the meters read high. The output should be 12.5v and there is a trimmer on the PS board to adjust it. Measure the output on the red lead at Pin 01. It's the one that the big cap connects to. There is no mention of this adjustment in the service manual.

- Pete
 
You must adjust the tuner power supply first! Then do the adjustment for the input level (VR01 and VR02), Requires a signal generator with an 80mv output. Then adjust VR601 to adjust the output level, then adjust VR3 and VR4 to center the meters. That should calibrate the Dolby system.
 
Thanks Pete & Jim,

Did haven't have a signal generator. I used my cassette deck that generates a 400 htz for dolby and adjusted output to 80mv. Fed to aux input, and did the input adjustment. All VR on the dolby board had the clothe coverings. Both channels were off 520mv 600mv. I then activated the dobly on the 9090db, the dolby meters then read left 17db, right 5db. vs -2db left and 3db right.
This is were I probably went wrong. The manual says to adjust VR 601 at Tape 1 REC terminal to 270mv. What Jim just said is that it adjusts the Output. I had VTVM measuring the REC Left 339vm, adjusted to 270mv, Rec Right read 341mv adjused to 270mv. Read Left it then read 341mv. Went back and forth until both the Left and Right read aprox the same, which was 291mv 310mv. I then adjusted the VR03 and VR04, to center. That was yesterday afternoon.
This morning I read Jim's post and remeasured everything. Everything was the same except VR601 adjustment the Left Reads 340mv, and the Right reads 404mv. The Left Dolby Meter is hair line below 5db. When adjusting VR601 what channel left or right is adjusted too, and the is VTMV is attached to the Tape 1 REC or to Tape 1 Playback.

Thanks,

Bob
 
The output level is measured at the REC terminals. The input level controls VR01 and VR02 need to be adjusted first they will affect the VR601 adjustment. When adjusting VR01 and VR02 you need to make sure the input to each channel is the same. If the input adjustments are not the same then the adjustment for VR601 will not be the same as that signal flows through the VR01 and VR02 adjustments controls. VR03 and VR04 are adjusted last and are only for the calibration of the meters. These adjustments will not adjust the output but the others will affect the meter calibration.
 
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