Marantz SD9000 / SD9020 / SD8000 / SD8020 Compudeck Optical Sensor Repair

Mirror of webpage here... http://members.cox.net/dpeters30/sd9000_pg4.htm

I have copied all the original pages into one page to make it a bit easier to navigate...

Please note: I just bought one of the Marantz SD9000 DBX units 's on eBay (March 2011) and my problem was related to belts and general maintenance not the opto couplers as described in this article.

The Marantz SD9000 is a very impressive deck. See my website www.pdemara.com for pictures of this deck and some of my other vintage gear.

Issues with my SD 9000 deck...

Interestingly both Fast Forward and Rewind worked fine on my unit as soon as I plugged it in.

When I push play or record the take up reel would try to turn a bit, but because the drive system needed a good cleaning it would not turn enough to keep the deck in play mode.

If I press play or record and manually turn the take up reel, the deck would stay in play / record mode. As I said prior to cleaning it would almost turn but didn't have enough tension to turn the take up reel.

If you have one of these decks and FF and Rew work ok but not play / record, it may just require a new main belt and some good cleaning of the tape mechanism.

Maybe one day my opto couplers will fail but for now my Marantz SD9000 cassette tape deck is running great. Feels like 1982 all over again. :-)

A thorough mechanism cleaning and head demagnetization and things are good as new.

Ah the wonderful sound of a 3 head ANALOGUE cassette deck.

Best regards,

Paul DeMara

March 2011
Overview:
Initially offered in 1980 as the flagship of Marantz's cassette deck line, the SD9000 Compudeck was one of the best-built, most feature-packed cassette decks ever offered for consumer use.  Retailing at $900.00, the SD9000 utilized two DC servo motors for precision tape control and three heads for direct tape to source comparison as you recorded.  Way ahead of it's time, the SD9000 also incorporated an advanced microprocessor-controlled music search feature, allowing you to program which songs on a given cassette you wanted to listen to, as well as the order in which you wanted to hear them. The SD9000 also offered a digital timer function for automatic timer recording or playback - accurate to the minute. In addition, the SD9000 included a slew of other advanced features like bias fine adjustment, an auto tape slack removal circuit, mic/line mixing, electronic timer memory, solenoid-controlled, full-logic transport, and the list went on. The Marantz SD8000, a slightly more economical choice, shared virtually all the features of the SD9000, however in a two-head design.

A Fatal Flaw?
Unfortunately, over the years, the SD9000 and its little brother, the SD8000 proved to have an "Achilles' Heel". Both decks used a pair of optical sensors to generate reel turn count pulses for their onboard microprocessors.  This microprocessor also interpreted lack of these pulses as a signal that the end of the cassette had been reached, and would send send an "all stop" command to the transport 1.5 seconds after pulse cessation. After 10 years or so, depending upon use, these optical sensors (also known as 'optocouplers') would weaken and fail.  The symptom? After one to two seconds in any mode, Play, Rewind, or Fast Forward, the deck simply returns to the Stop mode.  Over the course of 25 years, the failure percentage of these optocouplers approaches 100%. Worse than almost certain failure of these key components is the fact that the original replacement optocouplers are now no longer available, rendering these expensive cassette decks essentially useless.

Fortunately, these decks can be brought back to life with commonly available parts, about an hour of work, and a little patience.  Here's how:

Tools/Supplies You'll Need:

  • Soldering iron - a smaller 15-20 watt iron is ideal
  • Solder - "60/40" rosin core is the stuff you want (never use acid core solder for electronics!)
  • Solder wick - get this at Radio Shack or your local electronics supplier
  • 90% isopropyl (rubbing) alcohol
  • Q-Tips - about a dozen or so
  • #1 and #2 Phillips screwdrivers
  • Small #1 or jeweler's flat-head screwdriver
  • "T10" Torx screwdriver or 2.5 mm hex key (Allen) wrench, or 3/32" hex key wrench - any of these will work
  • Small wire cutters (I use an old toenail clipper!)
  • Long-nosed pliers
  • Regular pliers or small crescent wrench

Parts You'll Need:
Optek makes an optocoupler with suitable specifications in all criteria for this application except for physical size - it's too large (full manufacturer's data sheet is available here). We'll need to modify it as will be seen later.  Go to www.mouser.com, and in the "Part # / Keyword" search box, enter the following part number: 828-OPB818, or click here. Order at least two; at $2.37 each, I'd order a few extra for spares, just in case you damage one during the modification. Mouser has no minimum purchase, and the USPS Priority mail shipping option they offer will get you these parts quickly and cheaply.

By the way - it probably isn't a bad idea to order a replacement belt kit for your deck while you're waiting for your optocouplers, since you'll be deep into the tape transport anyway. I've ordered several sets from Bob at Vintage Electronics with good results.  Current price at this writing is under $20.00 per set, including shipping.

The Fix:
1.) Okay, let's get down to it! Start by removing the top three case screws with your #2 Phillips, shown below:

 
2.) Next, remove the two case screws on each side:
3.) Remove the outer metal case and set it aside.  Remove the hinging plastic tape head shield (if you're lucky enough to still have one). Remove the knurled finger screws from the front panel (see yellow arrows below). These screws secure the top metal "Marantz" panel and the lower clear plastic head adjustment cover - remove them and set them aside.

 
4.) There are two recessed Torx screws holding the plastic cassette housing assembly in place (see arrows below).  

 
5.) If you don't have a T10 Torx screwdriver handy, a 2.5 mm metric hex key wrench will work.  If you only have English hex key wrenches, a 3/32" will be a bit loose, but should still work.

 
6.) Tilt the cassette housing forward (catch the Torx screws you just loosened as they fall out), and set the assembly flat as shown below.

 
7.) Locate plug P508 on the main control board as shown below, and unplug it. This is the connector for the switch panel you just removed in step 6.

 
8.) Thread the P508 connector down through the other wiring while gently pulling on the cassette housing (see below). You may need to cut some wire ties to do this. Fish the connector through the opening below the cassette transport mechanism and set the entire plastic cassette housing aside.

 
9.) Remove the two cassette transport assembly securing screws shown below.

 
10.) Flip the deck over and remove the four remaining screws holding the tape transport in place (see below).

 
11.) Turn the deck right-side up again, and locate plug P503, as shown below.  Remove it gently. Always grasp the plug body, not the wires, when pulling.
 

 
It's a really good idea to mark the connector designations on the connectors themselves, since it is possible to plug a connector into the wrong receptacle on this model. 

 
12.) Remove and mark connector P502.

 
13.) Next, remove and mark connector P501.

 
14.) The last connector, P206, is located on the lower board, below the microprocessor board. Resist the temptation to just yank on the wires, and use your long-nosed pliers to disconnect it.

 
15.) To give yourself enough room to maneuver the tape transport out of the deck where you can work on it, you'll need to remove the four Phillips-head screws holding the power supply board in place.  The first two are shown below:

 
16.) Remove the third power supply board screw, located between the power supply board and the microprocessor board.

 
17.) Remove the last power supply board screw, located towards the rear of the deck, between the power supply board and the microprocessor board.

 
18.) Gently move the tape transport assembly towards the back of the deck, then up and out,  so that the reel hubs clear the opening in the deck's front panel.

 
19.) Lift the transport clear of the chassis and place it on a towel to prevent it from being scratched. The signal wires from the record/play/erase heads will still be connected; be careful not to place stress on them as you maneuver the transport.  Remove the Phillips screw securing the motor driver board to the transport housing.

 
20.) Tilt the motor driver board up and pull it towards you (as in the picture below) to remove it from the slotted retaining clip on the far side of the board.

 
21.) Remove the Phillips screw securing the Motor driver board retaining clip, and remove the clip. Use a standard pliers to remove the brass threaded hex bushing (lower arrow, below), and remove the flywheel retaining bar.

 
22.) Remove the flywheel drive belt with a pair of long-nosed pliers that has been cleaned with a rag dipped in 90% rubbing (isopropyl) alcohol solution.  Try to avoid touching the belt if possible - the idea is to keep any grease on the piers or oil from your fingers from getting on this belt.

 

 
23.) Next, remove the three Philips screws holding the capstan motor assembly in place.

 
24.) Lift the capstan motor free of the transport assembly, and set it to the side.  Now would be a good time to clean the capstan motor pulley with some swabs and your 90% isopropyl.

 
25.) Pull the flywheel up and out of its bearing, twisting gently side to side as you exert upward pressure. Notice the belt residue on this particular flywheel - unless yours is perfectly clean, use swabs and 90% isopropyl to remove all traces of residue.

 
26.) At last, we have access to the two optocoupler boards (see yellow arrows below).  Before you remove the board nearest the solenoids, scribe a pencil line (see red arrow) along the outer edge to capture the correct mounting angle to facilitate reinstallation.

 
27.) With your smaller #1 Phillips screwdriver, remove the optocoupler boar nearest the solenods.  There is a washer underneath the board used to properly space the optocoupler away from the reel hub.  Make sure you don't drop it into the transport when you remove this bord.

 
28.) Remove the second optocoupler board.  This one has no washer below, and has a positioning "key", so you don't need to scribe the mounting angle as on the previous board.  You can see the mounting angle mark for the first board below (yellow arrow).

 
Here's the culprit - one of the two defective optocouplers.

 
29.) Desolder the four connections holding each optocoupler to it's board. Solder wick greatly facilitates this process by soaking up the excess solder.

 
A detail shot of the optocoupler board traces.  Note the transistor and diode markings; you'll need to refer to these later when you install the new components.

 
Note the size difference between the original parts (at bottom) and the replacements.  Since the replacements are way too large to be mounted as they are, we need to remove the internal components and mount them separately.

 
30.) The trick here is to safely remove the two internal components from their plastic housing with damaging them.  There may be better ways, but here's how I've done it, always successfully, in the past.  With your small #1 flathead screwdriver, gently pry the thin plastic coating away from the body of the housing until it breaks and you can remove it, piece by piece.  The internal components are housed at the outer edges of the housing, try to avoid this are as you chip off the outer plastic.
 

 
30. (Continued) We're about halfway done.  Notice the clear infrared (IR) LED is already completely exposed.  Continue removing the outer case until all that remains are the two components and the internal alignment housing.

 
31.) Here's the new optocoupler with the outer covering completely removed.  Slide the two components out of the alignment housing as shown.

 
The component parts of the new optocoupler are identified below.  The alignment housing serves a dual purpose; that of properly spacing the LED and photo diode, and also providing a "mask" for the beam transmitted from the LED to the transistor. Without these masks, the beam path would be more susceptible to interference from outside light sources, and would provide a less accurate switching pattern.  So, while we can't use the alignment housing in our application, we do need those beam masks...

 
32.) With your long-nosed pliers, grip one of the beam masks as squarely and as close to the base of the alignment housing as possible and gently break it squarely off.  Repeat for the other mask.

 
Below is a detail shot of the devices with their masks. While it's difficult to see in these pictures, both the clear LED and the black photo transistor have a small bump on one side.  Once installed, these bumps must face each other to complete the light path. The beam masks, shown next to their respective devices, have a corresponding indentation to accommodate these bumps so that the masks may mount flush with the devices. The next step is to attach a beam mask to each device.

 
33.) Place a pin-head sized dab of superglue on the photo transistor, just below the 'bump', and apply the beam mask.  Make sure it's square with respect to the transistor, and press firmly together for about 30 seconds until the glue sets.

 
34.) Repeat step 33 with the infrared LED.

 
35.) And, of course, repeat for the second set of optocouplers.  The finished products are shown below.

 
36.) Mount the first set of devices to the first optocoupler board. Insert leads for one of the IR LEDs (clear backing) into the holes designated by the diode symbol; insert the photo transistor (all black) into the holes with the opto sensor symbol.  Ensure that the holes in the two beam masks are facing each other, then solder one lead on each device to the board.

 
37.) The purpose of soldering only one lead on each device is to allow you sufficient flexibility to align the two devices. Use your long-nosed pliers to gently adjust both devices so that they are parallel to each other from an overhead perspective, as shown below.  This alignment is not absolutely critical, but do the best you can.

 
38.) Now, ensure both devices are perpendicular to the board and thus parallel to each other from a side view.  Once you're satisfied with the alignment, solder the remaining connections and clip off the excess leads. Repeat for the other set of optocouplers.  It's a good practice to clean excess flux from your solder joints with some isopropyl alcohol; I find dipping a toothbrush in some, scrubbing the new joints, and blotting dry with a soft cloth works well.

 
39.) Remount the optocoupler boards to the transport assembly, being careful to remember the spacer washer for the board nearest the solenoids.  Use your reference mark (from step 26) to properly align this board before screwing it down.  Once both optocoupler boards are in, spin both reel hubs on the transport to ensure they move freely, and realign the optocoupler boards as necessary until they clear.
40.) Use this opportunity to thoroughly clean the transport and tape heads, since the transport is easily accessible. Now is also a great time to install brand new belts, so you won't have to take the deck all apart again in a few years.
41.) Finally, reverse the disassembly steps to reassemble the deck.  Fire her up, celebrate  with a beer, and listen to some old cassettes you haven't heard in a while. Congratulations! You've resurrected a fine piece of vintage audio equipment - may you enjoy it for many years to come!

(mirror of original web page here... http://members.cox.net/dpeters30/sd9000_pg4.htm

 

 

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