Aiwa AD-F770 Belts Replacement & Idler Wheel Fix

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Posted in TechnologyAudio

Introduction: Aiwa AD-F770 Belts Replacement & Idler Wheel Fix

About: Semi-retired electron wrangler/geeky aerospace engineering type.

I recently dragged my once-beloved Aiwa AD-F770 cassette recorder from the attic with a view to putting it on eBay but soon discovered that it made a high-pitched motor whirring noise when powered up.

The fact it powered up at all was quite heartening but there was obviously a problem and this turned out to be 'melted' drive belts. This appears to be a common problem if Google search results are anything to go by, so I found a supplier (see 'Parts'), ordered the belts and did some research.

A quick Google turned up a number of YouTube videos showing how to change the belts, but I generally prefer step-by-step guides, so I thought I'd put this Instructable together to document my (as it turned out) successful repair.

As can be expected with these types of repair, the anticipated quick belt change evolved into something more time-consuming. In my case this involved a partial strip-down of the tape transport mechanism to rejuvenate a defective idler wheel and to unjam the feed side pinch roller.

This Instructable therefore details the quick-fix belts change (where the tape transport is left in place) and then covers the removal of the mechanism to get at the aforementioned idler and pinch roller. Obviously the latter will also give you access to change the belts but if you only have to change the belts, use the quick-fix method as it is easier and quicker.

It almost goes without saying that a YouTube video and a forum or two helped get this repair going. I've linked to the ones which were of most help.

Step 1: Parts and Tools

Parts:

Tools:

You'll need a modest set of workshop tools:

  • 0pt & 1pt Phillips screwdrivers
  • Custom screwdriver tool (if you're leaving the transport mechanism in place) - see my Instructable here. This comprises a modified clothes peg, a 0pt Phillips 1/4" screwdriver bit and a 4mm / 4BA open-ended spanner.
  • Jeweller's screwdrivers.
  • Bright work light(s)
  • Binocular magnifier (very useful)
  • Caliper (not essential but could save some guesswork)

Consumables:

  • Cotton buds (for cleaning gunk).
  • IPA (IsoPropyl Alcohol tape head cleaner)
  • Metal polish (eg) if you have a corroded pinch roller shaft.

Step 2: Remove the Lid and Admire the Mess Inside...

Remove the three screws on either side of the case and the two at the rear,

Remove the lid and gasp at the mess. They don't make audio equipment like this any more!

The three photos of the tape transport show where the belts were. I'd previously removed them in an effort to measure their dimensions but this turned out to be futile as they were in a melted, gungy state.

Step 3: Removing the Power Switch

To access the screws securing the rear plate of tape transport mechanism, you need to remove the power switch.

Undo the screw (marked) and gently ease out the switch as shown.

Step 4: Remove the Screws From the Rear of the Tape Transport

To remove the screws with the mechanism in-situ, you'll need a 0pt Phillips 1/4" screwdriver bit and a 4mm / 4BA open-ended spanner (see my Instructable referenced in the parts list).

The screws to be removed are circled in red on the photos. They're all the same length except the right hand one (looking from the rear of the recorder).

Unscrew them using the custom tool (or via your own method). The top screw can be removed using a conventional screwdriver.

Step 5: Remove the Tape Transport Rear Plate

Gently ease the plate away from the rear of the tape transport mechanism. This permits access for cleaning the black belt gunge...

Step 6: Clean the Motor Pulley and Flywheels

Using cotton buds and IPA (IsoPropyl Alcohol), remove the melted rubber and debris from the motor pulley and flywheels.

Change the buds frequently. The rubber deposits usually come away nicely but take your time and be thorough.

Don't be tempted to scrape away the larger deposits with your fingernails. I did and it took me longer to clean the gunk off my finger than it did to clean the flywheels. You've been warned!

Once the wheels are nice and clean, it's time to fit the belts.

Step 7: Fitting the Drive Belts

The drive belts come in two lengths. The slightly shorter one goes on the flywheels and is fitted first.

The belts should be fitted as shown in the photos. I used a plastic case opening tool I bought as part of a kit to guide the belts into place but anything small with a right angle could do at a pinch (eg) a small allen key or a bent piece of coat hanger wire. Plastic is ideal though as it's unlikely to nick the rubber of the belts and/or scratch the mechanism.

The second (longer) belt should be fitted around the flywheel first then dragged onto the motor pulley as shown.

Once you're happy the belts are fitted correctly, you can refit the back plate.

Step 8: Refitting the Rear Plate and Seeing If Everything Now Works

Offer up the rear plate and once you're happy it's in the right place, refit the screws. I started with the top screw as it's the easiest and will hold the plate in place whilst fitting the lower screws.

Remember that the long screw goes in the right hand side.

At this point, you should be in a position to power up the recorder and check you've restored it to working order. However, as mentioned in the introduction, I found that although the capstans did indeed now work as they should, the fast forward/rewind didn't and I then found the feed side capstan pinch wheel was jammed.

This sort of thing should be expected of old tape decks and their ilk and it's quite probable you'll find something similar. Tackling this requires the removal of the transport mechanism from the recorder but it's not that big a job as you will see in the next part of this exciting Instructable...

Step 9: Removing the Tape Transport Mechanism Part One

Remove the six screws securing the mechanism on the chassis.

The top two screws are 7mm long, as are the bottom screws nearest the fascia. The remaining two are 5mm long.

Step 10: Removing the Tape Transport Mechanism Part Two

Gently ease the transport mechanism out as shown in the photo. You shouldn't need to use any 'assistance' (such as levering with a screwdriver), it's just a matter of manoeuvring but make sure the attached wires aren't trapped or hooked around the circuit boards.

Once the mechanism is free, you'll have enough slack on the wires to lay it flat on top of the circuit boards. After the photo was taken I rested the mechanism on a small cushion cover to protect it and the circuit boards from mutual damage.

Step 11: Remove the Cassette Drawer

To get access to the idler wheel, you need to remove the cassette drawer. This is probably easier than it looks.

Using the photo as a guide, gently ease the top of the cassette drawer away from the brass locating spigot, first on one side, then the other.

Moving down to the hinge, do likewise to the lower spigots. My photo isn't very clear but make a note of how the lower spigot engages with the drawer - it's not very intuitive.

Next, remove the screw holding the damper in place (circled in the second photo) and remove the damper assembly.

You should now be able to remove the drawer and place it next to the transport mechanism (it's held on by wires, so you don't have too much choice!).

You now have access to (some of) the inner mechanism. What you do next depends on your circumstances and the following steps cover what I had to do, so may not apply in your case.

Step 12: Removing the Idler Wheel

This in my opinion is the only tricky bit.

The idler wheel is the one shown arrowed in the photo. This is usually where the problem lies with a non-working FF/REW issue and in my case was because the rubber periphery had hardened so it wasn't able to grip the motor pulley and hub wheels.

This is how to remove it:

Ease the sliding plate out of the way (first photo) by displacing the angled metal lever and then gently easing the plate connected to the tape heads over the black piece of plastic in the middle and to one side. Hopefully the photos make this clearer.

The idler wheel is held in place by a spring, a washer and a split washer.

Place one fine jeweller's screwdriver on the idler wheel spindle and keep it there. This does two things - it keeps the wheel in place whilst you prise the split washer gently off the spindle with the other fine jeweller's screwdriver and (most importantly) it stops the split washer, washer and spring from shooting high into the air and becoming lost forever, thus forcing an early termination of this Instructable.

Assuming this hasn't happened, place the spring and washers to one side.

Removing the idler wheel from its spindle can be done without any forcing. I was able to ease it off the spindle with a screwdriver and work it past the take up spool hub. It does come off!

Step 13: Fettling the Idler

After cleaning the wheel with some IPA, it was obvious the rubber had hardened. I read a tip on a forum where the poster had claimed success by simply twisting the rubber ring so that its outside was now on the inside, exposing fresh(ish) rubber to the outside. I tried this but it didn't work for me, so the choice was either to buy a new rubber wheel (possible source here) or increase the diameter of the current rubber wheel slightly by putting some packing next to its inner surface.

I did the latter which worked a treat. However, I'm impatient and a prudent person would of course buy a new one - after all, we're talking 1980s rubber here!

If like me you're impatient, read on...

Disassemble the wheel as shown in the photo and clean the parts with IPA.

The inner diameter of the rubber ring is 10mm, so using Pi*D I calculated the wheel's circumference as 31.4mm.

(The dimensions of the rubber ring are: OD: 13mm; ID: 10mm; thickness: 1.65mm; height: 2.4mm).

I cut a strip of self-adhesive metal tape* (purchased from Aldi years ago) 31.4mm long and 2.2mm (approx) wide and placed it on the idler as shown. Metal tape is good as it is relatively stiff and less likely to buckle than say, insulation tape. The tape was 0.3mm thick so adds 0.6mm to the idler wheel diameter.

* this tape is quite thick, so if yours is thinner I'd suggest doubling the length and doing a double wrap.

Refit the rubber ring with its fresh side outwards (see above). Before refitting it (a reversal of the last step - don't forget to guard against spring and washer escape attempts), add a very light coating of silicone grease to the spindle and clean (if you haven't already) the fast fwd/rew motor pulley with IPA.

Step 14: Fettling the Feed Pinch Roller

The feed capstan assembly is circled in the first photo. As it incorporates a tape guide, measure the length of the screw protruding at its pivot point so when reassembling, you can get the tape guide in the correct place. An alternative (which I used) was to measure the height of the underside above the chassis (shown on the photo). In my case this dimension was 14.45mm.

If you don't have access to a caliper, count the number of visible threads where the nut screws on. On reassembly, you can then tweak the height when playing a tape with lots of treble on it. The nut is accessible from the outside.

Another thing to do before removal is to note carefully where the two springs attach at either end. Take some photos just in case.

Removal is simply a matter of undoing the nut and sliding the assembly off the post.

Once removed, you'll then have to disassemble the roller itself. To do this, I found a broken drill bit of smaller diameter than the roller shaft and drifted the shaft out using light taps from a small hammer.

The shaft came out a little grudgingly and the photo shows why.

Clean the roller with IPA and the shaft with metal polish. Again, a very light film of silicone grease should be applied to the shaft on reassembly (take care not to get any on the rubber of the pinch wheel as it's very problematic to remove). Check the wheel now turns freely.

Refit the assembly to the transport and adjust the height using the measurement you took before disassembly..

Step 15: Refitting the Transport Mechanism

Refit the cassette holder - start at the top by re-engaging the brass spigots and then re-engage the spigots at the other end (you have to close the holder's drawer slightly to get the holes and slots lined up).

Refit the damper.

At this stage, I'd check everything you've worked on is now functional - this is a bit risky as you have to make sure the transport isn't touching the circuit boards etc. - rest it on some insulating material and make sure the moving parts (mainly the flywheels) are free to move. Insert a sacrificial cassette and power up the deck. Check fast forward and rewind both work and then try play. If all is well proceed as below. If not, I wish you good luck in your fault tracing!

Switch off power and remove the plug from the wall outlet.

The transport can now be refitted into the tape deck - this should be done carefully with no forcing. Make sure none of the attached wires get snagged and pay attention to where the tape head wiring fits in a slot under the cassette drawer hinge.

It should just go straight in but if you struggle, don't worry - take your time and it will!

Step 16: Testing (and a Few Thoughts)

Once fully reassembled, it's time for testing.

As before, I'd start with a sacrificial cassette but if all is well, you can dig out your old tape collection and reacquaint yourself with a previous life.

Once you're happy with the height of the feed pinch roller, dob a bit of clear nail varnish on the fixing nut to stop it wandering over time.

I'd forgotten just how good this deck is and I'm now reconsidering whether eBay is the right option for this lovely piece of kit. Having said that, track selection requires patience.

The thing I find interesting is that these (mostly) thirty to forty year old tapes play back very nicely (once run through backwards & forwards) and despite the advice of the professional tape recording community, don't appear to leave their oxide all over the tape heads and capstans.

I hope you found this Instructable informative & helpful and I welcome all constructive comments!

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