Infinity walkman restoration

Hello,

This will be a step-by-step guide to repair the Infinity Intimate Stereo walkman. This unit is special because it was the world's first to feature Dolby B noise reduction. It has a beautiful design typical of that era

Capacitors list (height x diameter):

100uF (7 x 5mm)
47uf (7 x 5mm or smaller)
33uF (7 x 3mm)
22uF (7 x 3mm)
10uF (7 x 3mm or smaller)
4.7uF (7 x 3mm or smaller)
2.2uF (7 x 3mm or smaller)
1uF (7 x 3mm or smaller)
0.1uF (12 x 5mm or smaller)

1. Take the battery cover out and proceed by taking out the 6 screws that hold the back cover on. After that, carefully remove the battery terminals from the back cover and remove it completely.

2. This will be the most time consuming part, as you need to note which wire goes where, as most of them will need to be desoldered to recap the main board.
When I repaired the walkman, I did a hand drawing of the board noting each wire's color and where it needs to be soldered. You need to keep in mind that there may be more wires of the same color (I found this to be the case), in which case you need to note additional information, such as where it goes on the other end or if the wire if thin or thick. I also took pictures as a backup. Also do not take my pictures as a reference, as it may vary from a unit to another.
This step is absolutely critical, as you will not find a schematic for this device.

3. Take out the board bewlow the motor toghether with the flex cable and the thin board that attaches to the mechanism. At this point, if you have all the wires desoldered, you can also take the main PCB out.

4. Take the cassette lid cover off (it has 2 black screws)

5. Take the last screw (silver) on the bottom right of the mechanism out. After this, the mechanism is only held in place by 2 plastic nipples on the back. You need to bend the plastic 1-2mm to take the mechanism completely out of the case.

6. At this point, the audio power amp board together with the volume pot can also be taken out.

7. The front and back side of the case toghether with the cassette lid can be cleaned and polished at this point. It is to be noted that the chrome paint in front of the cassette lid will easily dissolve if polished. Same with the writings on the case (they fade harder than the silver line), so do it to as your own preference or just give it a good clean.

8. Take the back plate of the mechanism out (has 4 screws). On this plate you need to do the following: clean the rubber tires of the FF/REW gears, put oil on the spindles. I do not have a picture with this backplate at this point.

9. Take the flywheels out, the clutch assy and the second belt. At this point you can lubricate the table reel spindles and clean their rubber tires (for accessing the table reels the front plate must be taken out - note a white plastic part that drives the TAPE/RADIO switch, as it can easily fall out.

10. Shorten the clutch assy spring by cutting 1-2 coils. The clutch spindle must be lubricated with oil and the belt groove cleaned. Also clean the flywheel bushings and lubricate them. At this point you will need to reinstall the small belt.
The spring will need to be shortened even if you replace the rubber tires, as in its original length it applies almost no pressure at all on the rubber ring.
I do not have its dimensions, as I have used one from a pack of many belts (flatnees of this belt is not critical, unlike the large capstan belt).
The belt needs to be a little loose, as it will tighten when PLAY is engaged and cluch assy moves in place. If the belt is too tight, it will act like a spring, counteracting the force of the clutch assy spring, lowering the takeup torque to the point that it will chew up your tapes.

11. Clean the flywheel, idler and motor pulleys grooves and install a new capstan belt (I used an 88 x 1.2mm in mine, which is on the tight side, so I suppose that any belt between 88 and let's say 92mm will do the job). After this, you can oil the motor upper bushing and put the back and front plates back in place.

12. The next thing to do is clean the volume pot with contact cleaner and recap the power amp board. Note that it is likely to find corroded traces, that will need repair. After this step, you can proceed to put the power amp board and volume pot back in the case, followed by the mechanism and cassette lid.

13. The next time consuming part is recapping the main board. Here, it is also likely that you will also find corroded traces. Also, after taking old capacitors out, clean the board well with cotton swab and IPA. I recommend replacing one at a time (or all that are the same value), to keep track of which one goes where. It is also possible that the Dolby adjustment trimmer has some corrosion on it. If so, spray some contact cleaner on it and wipe the green residue with a cotton swab (let it sit for a couple fo minutes for the corrosion to dissolve). You may need to repeat the process a few times to get it clean.

14. Resolder all the wires going back to the main board and reassembly the board with the 2LEDs. In one of my units, the TAPE led was getting old, flickering every once in a while, so I searched for replacements. They are 2mm LEDs, which can be easily found online. I decided to replace both, to have the same brightness.

15. At this point, you can power up the unit (note that the DC plug is center negative) to test it, clean the capstan, pinch roller and head. If everything works as expected, you can proceed to adjust the tape speed (there is a small plastic cap above the motor; remove it and use a flat screw driver for adjustment).

16. Dolby adjustment: Given that a service manual or schematic for this unit cannot be found; I could not find any info on the Dolby hybrid IC (NC 8500) either, so decided to go on an alternative route, as playing a Dolby tape sounded noticeably muffled. Given the fact that there is only one trimmer pot, I suppose that what it does is not adjusting the Dolby level, as in other walkmans I have repaired, but the reference voltage. I will describe the procedure that I came up with, mentioning that it is how I did it and not necessarily the best way to do it.

- I grabbed an azimuth adjusment tape (6.3Khz -10dB). Used this because it's something that is easily available.
- I made measurements playing this cassette on a calibrated deck with Dolby OFF and with Dolby ON, noting the ratio between the two.
- I adjusted the trimmer pot to obtain the same ratio as in the reference unit. Rotating clockwise decreases the ratio, rotating counterclockwise increases it.

After I made this adjustment, playing a Dolby encoded tape sounds completely neutral, as it should.

So, this is it, I hope you enjoy it and can help other people repairing this fantastic walkman !

 

I had no idea either, the seller sent me a different unit than the one in the pictures, but in the end I was happier with having 2 different ones.
From what I have seen internally, the dark brown seems to be a newer version, since it uses a flex cable instead of just wires connecting the 2 boards on top of the mechanism.

It is to be noted, for people who want to have one, that there are units available on ebay from time to time. The best part is they are usually sold at insanely low prices, given how rare they are.
I paid about 50$ for the dark brown one and about 30$ for the light brown. The first was being sold either as functional or as not tested, I don't remember which (of course none of them was functional in reality).
Of course, I took it apart before trying to turn it on.

 

Whan an interesting layout inside! I've yet to open my Akai, now I'm excited to...

 

@Mister X I did the restoration process on both, actually. I think I forgot to mention that. None of them worked initially, the main belt was too stretched to drive the capstan and all the capacitors leaked. Given what I found when taking the back cover off, I did not even try to power them on, but just proceeded with further disassembly.
Initially wanted to put pictures with just one of them so it's not confusing, but decided to put both since many people probably don't know 2 variants existed.

@stuck-in-time It would be interesting to see some AKAIs taken apart, they're pretty rare... This Infinity Intimate is most likely made by AKAI for Infinity, because it's 90% identical to the AKAI PM-01, except for the Dolby NR and hotline feature (the AKAI doesn't have Dolby, but has the hotline).

Something else interesting I rememebered having are 2 pictures with the Panasonic RX-2700 mechanism (found last year on shizaudio.ru), which is an almost identical (except for the buttons) AKAI-type mechanism. So most likely this mechanism was used on other walkmans and mini-boombox type devices (I doubt it's made by Panasonic).

 

I'll take pics once I get inside. I remembered some of its body screws were stuck, so I haven't touched it since.

Ah! Thanks for the link. I've been looking for this thread since it disappeared.

 

I'll read it for sure, there's a lot of information in there. I did not know about it.

It makes a lot more sense now: I just searched for "Cybernet walkman" and found that they even had a model called Intimate (probably the model name is also taken from there): https://www.radiomuseum.org/r/cybernet_mini_concert_ps_101.html
It looks extremely similar to the Infinity, most likely the entire walkman was made by Cybernet, not just the mechanism. It's clear that both AKAI and Panasonic sourced at least that mechanism (maybe also the electronics) from Cybernet.

This Cybernet Young Man looks almost identical to the previous one: https://stereo2go.com/forums/threads/cybernet-young-man-ps-101-1981.2932/

 

Well that's a good read and thread revival