IDIOSYNCRASIES and REPAIR TIPS
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
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
Figure-1: The auxiliary brakes
used in the ALPS mechanism.
Primary brakes and clutches are part of
the reel-table assembly (not shown).
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 ALPS mechanism.
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, http://www.eco-charge.com/ 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
ALL IN THE FAMILY
The following Panasonic machines all use the same transport:
PANASONIC SV-DA10 /
SV-3200, SV-3700 / SV-3900
and SV-3800 / SV-4100. The " / "
and the color-coding indicates machines of the same "family."
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
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
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
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 lapping film.
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
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
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 particles.
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 switches.
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
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. In 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
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
"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 record…
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
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
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