Compact Cassette - Technics RS-B48R Recertify
Power Up and test play.
These tests are made using scrap tape, and a pre-recorded tape. The deck functions as expected in both directions, the tape path looks clean, and the rollers look okay. A short test recording indicates that the machine is functional for recording and reproducing in both directions and that the noise reduction systems operate. Looking at the owner’s manual I can see that fundamentally the machine is meeting operational requirements.
Check for Wow and Flutter
For a rough check, I use a 1 kHz -10db test tape. At this stage I am listening by ear for obvious worn belts and pinch rollers. Of course, the condition might have been indicated in the test play step above. In this case I think I did hear a little warble, so now on to the next issue, look inside.
Remove the cover and look for worn belts, hardened grease, and worn rollers in the tape drive. Often a simple application of a tiny bit of rubber cleaner/dressing can allow you to avoid replacing rollers and such. Any lubrication should be very slight.
On these machines, a bit of sewing machine oil on the capstan bearing, and on the cassette hubs can be very useful. Apply this oil using a needle. Of special note do not clean capstans with alcohol, as this can run down into the bearing and dry them out. Slightly moisten a swab with methanol and clean the capstan[s] with an almost dry swab. This may have an ever so small beneficial impact on the wow and flutter of the machine.
On this machine, the belt does look worn. The rplacement belt I have does not look like the same width, so I am not sure this is going to be worth trying. At this stage, a more detailed wow and flutter evaluation is needed. I do have a test tape and a Leader Wow and Flutter meter, so this will be the next step. I am going to diverge a bit here and talk about another technique. Before I commit my wow and flutter tape to this project, I want to see if the machine tracks the tape appropriately.
There is a magnetic ‘developer’ that can be used to show the magnetic pattern on recorded materials. I am going to bulk erase a cassette I have reserved for this purpose, and make a 100 hZ square wave recording in both stereo directions. Then I will develop the recorded signal and see where the record/playback head traces the tape. This won’t show azimuth, but it will show the tracks the machine puts down on the tape, and of course where on the tape it reads also since the record play head is the same. Since this is a reversing machine I will record in the reverse direction also. I am not concerned about levels here, so I will just use a signal generator and use the decks own ‘vu meters’ as a guide to the recorded level.
The developed magnetic tracks look very good, exactly centered and if you count the strips the tape speed is good. My concerns about the belt remain, but at least I feel confident about the tracking.
There is an adjustment for the head height, and there is a standards tape for that. Putting that standards tape in the machine, adjust the forward and reverse tape guide tracking using the screws.
The reference numbers from a Nakamichi are around -6db centered. Our machine measures -6 on both channels.
The next step will be to hook up the Leader Wow and Flutter meter and compare what we see to the specification in the Service Manual. We need to verify speed and wow and flutter. It should be noted here that there are two methods available for this test. We can either use a standard tape, or use the record playback method. I do prefer the latter because I am not yet convinced a standards tape has been recorded with a machine with low enough. residual wow and flutter to be of value when testing high end machines. This machine, the Technics RS-B48R is not that high end level though, so let’’s just see what we get using a secondary standard tape.
Here’s the setup – simply an in/out to the line in and out. Everything about level is automatic.
We got some preliminary readings with a secondary standard tape, and decided to do more in depth. Because I have more than one cassette machine in my system, it is important that the machines all run at exactly the same tape speed. I made a 3150 Hz speed tape on my reference deck, a JVC TD-V661 that has been restored to factory standard.
I played this tape on the Leader Wow and Flutter Meter just to be sure residual was good enough. I was able to get 0.02 wtd on the jvc, and when I played the tape on the Technics I was able to get 0.04 which does indeed align with the specification in the owners manual. All in all I think it is pretty adequate for the level this machine actually is. This reading is similar to the Systems standard wow and flutter tape. I am therefore convinced that my JVC made reference tape is good.
When I was playing the tape I did notice the machine was running a bit slow. On this machine the speed is adjusted by a small pot in the back of the motor. Using a insulated screwdriver, it is possible to adjust the tape speed so that the wow and flutter meter reads 0% drift.
With the lubrication of the capstan shafts, and a through cleaning, the mechanical side of this machine is now adjusted to specification.
This is the reason for buying a decent machine in the first place. You really don’t want to realign the tape path and rebuild mechanical parts on one of these finicky machines.
The Electronic Performance and Alignment
The Electronic Performance and Alignment
The next steps of evaluation of the Technics RS-B48R can be broken into two major groups:
Alignment of the playback system, and Alignment of the recording system. Obviously, playback alignment should be done first, and it will be a little more complicated by the fact that it must be done in both directions as this is a reverse capable deck.
Playback alignment consists of frequency response and levels.
To do the Playback system alignment we will need :
VTVM to measure levels
Scope to align azimuth
Test tape for azimuth alignment
Test tape for frequency response
User Manual and Service Manual to verify procedure and specifications
—
Generally, one should simply follow the steps in the service manual for electronic alignment. That is what we will do in this case.
Azimuth adjustment forward and reverse
Using a frequency response standards tape, adjust the azimuth screws so that the wave shown on the Oscilloscope line up. Start at the lowest frequency on the tape and proceed upwards. At the very highest frequencies it might be a little unstable, but get the average to fall into the waves
Once the azimuth is set, set the playback level. Connect a VTVM to the output and playback a standard level tape. Using the service manual get the required output at either the output jacks or a test point on the circuit board.
The playback level setting uses a standard tape, which we have previously verified on the JVC Reference deck.
Standard output is read using the VTVM per the Service Manual.
Recording Alignment
To fully experience the cassette system, recording is an important aspect of the setup. In order to align the recording electronics a few more pieces of gear are required:
Signal generator
VTVM
Calibrated Attenuator 600ohm
Oscilloscope
Again following the user manual procede through the adjustments.
This deck has not been adjusted so I am not going to adjust the bias at this time. It is a fairly straightforward process however.
I will touch up the record level controls however.
Connected as described. With a 2 head machine you have to record a bit and play back to see where you are, but tuning a little at a time you can narrow in on the correct setting. I then double checked the recorded tape in the JVC Reference Deck. It is right on the money. 0 Vu on both machines
This wraps it up, put the cover back on the machine and enjoy it knowing it is set up and running correctly. Of course, these finicky machines constantly go out of exact spec, so keep all the test tapes and gear handy for the next time.
And as always there is:
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.
Conclusions
Concluding comments
1. This page was done engineering notebook style – Someday in the future it might be added to and typed up
2. See our list of req test equipment for detail on the gear used
3 Take a look at some of our other re-certifications
This deck has been deleted from the system. The write up is still valid. The reason for the deck to be deleted was that i dropped it, and massivly bent the tape drive unit. Lesson learned be more careful… I might have been tempted to repair it, but the prices on the auction site are too low for me to want to preserve the unit.
if you want to know, when i refer to the ‘auction site’ what i mean, type auction site into the search bar….