DAT Machine IDIOSYNCRASIES
and REPAIR TIPS
last updated 24 Spetember 2004
by Eddie Ciletti
For its generation, the SV-3500 had a very reliable transport primarily
due to its optical mode switch and transport logic. All other machines
use electro-mechanical switches (which are failure-prone) to report
transport status back to the system controller. Many decks also operate
under capstan control in reverse play. While there is nothing inherently
wrong with this concept, it does become a problem if supply and take-up
tensions are out of specification. Sony's earliest machines — the PCM 1000
/ 2500 / D-10 (also from that period) — have separate reel motors, while
most transports derive "reel power" from the capstan motor through belts,
gears and clutches. Yuck! (Sony created an absolutely awful
transport — the PCM-2300 was no better as the "pro" version of several
consumer models. Then, Sony created the PCM-R500, which has separate
reel motors, and had a street price of about $1200.)
This is not a new cocktail drink, but it is a problem with older machines
whose rotating heads get “stuck.” This has been the case with the
venerable Panasonic SV-3500 and now, with the nearly vintage SV-3700.
It is much easier to access the latter — with the cover removed — by opening
the drawer halfway. If the head is stuck, just apply a little rotational
pressure in either direction. If you can stand the occasional inconvenience,
the head is otherwise functional.
COMPATIBILITY: Sony versus Panasonic
A misaligned machine will play its own tapes. ALESIS suggests
that users make their own "reference tapes" when the machine is new.
Format a new tape, date and test it for errors. Later, when a problem
arises, you'll be able to troubleshoot the problem rather than burning
precious brain cells. I suggest recording a pleasant, low-frequency
tone -- 40 Hz is very soothing -- across the entire tape, just to
confirm that something, in addition to absolute time code, is on the tape.
Test tapes are expensive, but a scope and a "home-made" reference tape
will get you in the ballpark. This
link shows how to make the connections.
Alignment issues usually show up when tapes are sent out of house.
Contrary to hearsay, while SONY and PANASONIC make their own transport
and calibration tapes, the end result — the alignment — is the same.
However, many SONY machines are less likely to hold their alignment and
should therefore be suspect. The SLANT BLOCKS are the cause of the
alignment problems. While this may be a frustrating malady, that's
almost ok, because when repaired — rather than replaced — the results are
better than new. This
link details the Mechanical Adjustments.
Panasonic was smart when designing the SV-3500 in that the pinch roller
is disengaged during reverse play operation. (Reverse-play is always used
when locating Start IDs because transports always overshoot the ID by several
seconds so as to not damage the tape.) Other machines that reverse-play
without the pinch roller engaged are the Casio DA-2 / DA-7, the Tascam
DA-P20 and the Denon DTR-100P. All of these portables use the same
ALPS mechanism that is also found in Tascam's "tabletop" DA-30, the
exception because it does engage the pinch roller in reverse-play.
(See Figure-1.) The problem with the DA-30 is that a "soft-brake"
is required to provide "back-tension" to the take-up reel table when it
becomes the "supply" reel (in reverse play). ALPS — an Original Equipment
Manufacturer, or OEM — never made this "soft brake" available as a replacement
part. A consciencious service center can cut a piece of felt and glue it
to a non-removeable lever — a tedious task, but worth it because the tape
is more delicately handled yielding faster recovery from shuttle mode.
Figure-1: The auxiliary brakes used in
the ALPS mechanism.
Primary brakes and clutches are part of the reel-table assembly (not
Loading problems have been common to TASCAM’S DA-30MKII and
the DA-P1 portable. Both use the same ALPS mechanism. Deep
inside the mechanism, a rubber belt the size of a dime links a motor with
a worm gear. The gear is sometimes over-lubricated. Gravity
combined with centrifugal force “spits” schmutz on to the belt causing
it to slip and eventually deteriorate.
PORTABLE LIFE SPAN
I’m no fan of the SONY “cigarette pack” portables. While these
are technical works of art, they are in no way affordably serviced.
Treat them with the utmost respect. Don’t loan ‘em to a friend and
please don’t drop them. The two most reliable and serviceable portables
are the HHB PortaDat and the SONY D-10 Pro.
Other cigar-box portables like the Tascam DA-P20 (and similar models
by Casio and Denon) are worth repairing. Less conscious humanoids
have been known to accidentally reverse and force the power connector causing
internal damage. Otherwise, most of the failures are mechanical.
Parts are still available because Tascam’s original DA-30 uses the same
Batteries and power supplies are no longer available for many portables,
but don’t throw out the “bad” adapter. If the cable and connector
are still intact, ECO-CHARGE @
800-361-5666 can use them to retrofit their external rechargeable
battery systems. Their battery prices are often as good or better
than the original manufacturer, about $65, with greatly improved performance.
However, because a new power supply is required, the initial investment
will range from $200 to $300. This applies to all the "discontinued"
models including the ALPS portables (Casio DA-2 and DA-7, Tasam DA-P20
and Denon ???) and the Panasonic / Technics SV-25x series (these require
the user to have an old battery to make the connection). Remember
what Groucho said, "the lord alps those who alps themselves!"
ALL IN THE FAMILY
The following Panasonic machines all use the same transport:
PANASONIC SV-DA10 / SV-3200,
/ SV-3900 and SV-3800 / SV-4100.
The " / " and the color-coding indicates machines of the same "family."
Click here for a schematic to convert the SV-DA10
to an SV-3200.
The SV-3700 DAT machine is old enough to warrant a bit of a history
lesson. From that same time period came the SV-DA10 ( a "black" face
consumer version with MASH converters). This machine records at 48kHz
only and has consumer (RCA) analog and digital I/O ports. The SV-3200 is
an SV-DA10 with a "cream" face, the same consumer rear panel and selectable
sample rates (44.1 khz and 48 kHz). Inside they are essentially the
same machine. An SV-DA10 can be modified to record at 44.1 kHz.
Panasonic’s DAT transport is more serviceable than some but harder to
clean than others. Figure 2a shows about what you'll see when
the cover is removed. This heavily doctored image clearly shows that
I have two left thumbs! Step 1: Apply both thumbs to the white
gears on either side of the loading cage. Move in the direction indicated
by the pretty blue arrow. Step 2: Apply a lint free cloth
dampened with 99% alcohol to the side of the head drum. With another
finger, gently rotate the head touching only the top of the drum.
Figure 2a: Panasonic's brand of head cleaning torture
For the more mechanically inclined, Figure 2b shows
how the loading tray can be swung out of the way to provide full access
to the transport. It’s even possible to play a tape using a rubber
band to secure it to the mechanism. Maybe you shouldn’t try that
trick, but it sure makes it easier to see what’s going wrong.
TALKING ‘BOUT "SHAFT"
Figure 2b: Service access to Panasonic family of transports
In the top left corner of Figure 2b, is a "zoomed-in"
view of the capstan motor shaft. This "Shaft" can be one dirty… (shut
yo mouth!) Not many machines come in looking this bad, but sometimes
I wonder which brand or batch of tape is responsible for such stubborn
Removing funk from the capstan is not easy and cleaning tapes are powerless.
Alcohol must be used sparingly to avoid dissolving the bearing lubricant.
I use a special "U" shaped screwdriver to wrap a cloth part way round the
shaft to get the dirt off. Real stubborn dirt requires a mildly abrasive
Typically, Panasonic machines have serial numbers that begin with letters,
such as "AA." Following the letters will be numbers, such as "0,"
"1," "2," etc., representing the year of manufacture, respectively,
'90, '91, '92. With this in mind, confirm the following:
1.) Locate the serial number. (It may be hidden by the rack mount
2.) Units made before 1993 ( SV-DA10, SV-3200, SV-3700 ) require a circuit
trace (see Figure 3a) to be cut and a back tension lever to be replaced.
Figure 3a: Panasonic Servo board
located on underside of the transport
of all models with the exception of the SV-3500.
An image of this lever (part number RML0090-1) will eventually
appear to facilitate identification.
3.) After removing the loading tray, look for bits of broken
cassette shell that might jam the mechanism. It's a good idea to turn the
entire chassis upside down and shake to make sure any loose bits will fall
out. Grease on the transport will sometimes trap potentially hazardous
4.) Inspect the Mode and Load switches. ( These report transport
status to the system control IC. ) One is located on a yellow pcb
near the capstan and the other is on the underside of the mechanism.
The contacts are gold plated, but the plating wears off. If the silver
traces that lead to the switch contacts have turned black, change both
One easy test is to connect a .1uF cap in series with an unbalanced
audio cable. Momentarily connect the cap to the switch wires and
listen while cycling the transport through its various functions (Play,
Rewind, Shuttle, etc.) The "normal" sound will be distinct (and very
loud) pops as the DC voltage switches fro zero to five volts. Any
scratchy sounds mean the switches are fatiqued. Test points and images
for Panasonic and other Manufacturers will eventually be provided here.
This test is particularly well suited to the Alesis ADAT.
5.) The primary and "soft" brakes are usually worn out
after one or two years, depending on use, and should be routinely inspected
and replaced. The reverse-play soft brake is located under the take-up
reel table. Only about 1/32 of an inch makes contact with the bottom
of the take-up reel table. I have a mod for this that requires the
addition of two washers. That information will also be made available.
the mean time, click this link for more details on the subject...
6.) Repeated tape jams will chip teeth on a large transfer gear
located on the underside of the mechanism. Unusual fast-wind noise
is a sign that this gear should also be replaced.
7.) There is also a possibility that take-up tension is either
too high or too low. A smooth ten to fifteen gram/centimeters is
good. Eight gm/cm is too low. Eighteen gm/cm is too high.
Variations are caused by a clutch (RXG0011-2). A new version of the clutch
has a red dot.
|GETTING OUT OF A JAM
One of the common causes of jamming — the machine's inability to eject
a tape — concerns the length of the back tension felt. Too long —
caused by a worn or misadjusted felt and/or by heat — causes the tension
arm to get in the way of the left loading/precision guide.
FIGURE 3b (above) shows the "crash site." Pushing the tension arm
in the direction of the arrow will cause it to rotate clockwise and out
of the way.
"Tally" is a term that describes machine status. It is part of the language
spoken within those multi-pin connectors that link machine-to-machine or
machine-to- "other" devices like remote and edit controllers. In
the pre-cyanide era, the most important Tally was a light bulb labeled
RECORD READY. If that bulb was dead, you’d be dead too after pressing
When an open-reel machine is in Fast Wind, no additional clues are necessary.
But ever since tape activity went indoors, we’ve relied on LEDs and LCDs
for feedback. I think most people will agree that more feedback would
be better, hence this simple mod for the Tascam DA-30.
All of us are guilty of pressing buttons when, quite often, the machine
is simply not ready. Wouldn’t it be nice to know that all products
could clearly communicate this "readiness?" Tascam’s DA-30
and DA-30 MKII have a DB-15 remote connector on the rear panel. Detailed
in the schematic (shown in Figure 4) as P1, "Control I/O,"
Pin 12 of the DB-15 is the STOP TALLY. It goes "low" (to ground)
when the machine is ready to do business. Connect the anode of an
LED to +5 volts (Pin 16 of either U801 or U802). In series with the
cathode is a 220W resistor that goes to pin 4 of U802 (also pin 12
of the DB-15).
Figure 4: Tascam DA-30 Remote COnnector schematic depicting
STOP LED modification.
Unfortunately, 5 volts does not appear on the DB-15 connector
or else you could do this without even opening the unit. (An external
supply seems silly doesn’t it?) I put the LED just above the stop
button on the machine’s front panel. If you get that far, there’s
an LED-sized hole in the plastic assembly just above the Stop button.
Just knowing that the machine will not accept any commands until the STOP
LED comes on will save wear and tear on your fingers, your already short
fuse and on that button assembly.
Tascam DA-P1 Portable
From the web comes a bit of enlightenment concerning the ability of
Tascam's DA-P1 to display Error Rate. Press
this link for details.
I love feedback in the form of email.
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