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by Jeremy Schrag
Back in the day, the Infinity II was the fanciest cassette based head unit Chrysler offered. With all its buttons and gadgetry, it represented 1980s audio technology at its most sophisticated.
Unfortunately, it ended up being a little too ahead of its time. Everything that made the deck so cool ended up also making it somewhat unreliable. So, when the 1990s got started, Chrysler went back to Mitsubishi and called for a redesign that was perhaps not so complicated.
It is that redesigned unit that I’m looking at today. Not quite an Infinity II, and not quite an Infinity III, this is a model all its own that somehow slipped in between the two decks for a couple of years. Offered as a premium head unit both with and without the Infinity speaker system, it is officially still known as the Infinity II though it does not bear Infinity branding unless it came with the speakers as well.
This particular example came from a 1991 Chrysler Fifth Avenue that did not have the Infinity speakers, thus the lack of Infinity branding on the front.
I’ve mentioned that this is a model all its own, and for proof we need look no further than the label. This model’s Mitsubishi name is the RX-691, or in this case the RX691S, indicating the silver button highlights. The original Infinity II unit went by the model number RX-690, while the Mitsubishi based Infinity III goes by the number RX-695.
The only two screws we need worry about here are to hold on the top cover.
The bottom of the deck. Again, all screws seen here are to fasten down the bottom cover.
The left and right sides continue this deck’s trend of minimal screws. Each side has a pair to hold the faceplate on, and that’s all.
The back panel has the usual connectors on it. The familiar seven pin black and gray connectors handle all the major connections, while an 8-pin DIN connector facilitates a connection to Chrysler’s single disc slave CD unit. Like the other Infinity decks of this vintage, this connector can be used to provide an auxiliary input. Please consult my original Infinity II article for more details on that.
The first thing we’ll do with this deck is remove the four screws on the sides and pull the faceplate off. This gives us the above view of the faceplate PCB (circuit board). We can’t remove it just yet, but we can get a look at it.
When we are able to remove it, it’s not hard. The purple arrowed tab must be de-soldered and bent away from the board, while the three green arrowed screws must be removed.
You can see two connectors along the top of the PCB - they are the reason the board cannot be removed yet. The three pin one on the top left is permanently fixed to the board, while the ribbon cable just above the vacuum florescent display is a bit hard to deal with. I prefer to detach that ribbon cable at the other end, which is found on the mainboard.
But to get at the mainboard, the tuner module has to come out. This module is a lot like the one found in the Mitsubishi version of the Infinity III. Unplug the two blue arrowed cables (one is a ribbon cable), remove the green arrowed screws, and just lift it out.
To remove the board from its tray, you need to go a bit further and twist the purple arrowed tabs in line with their holes.
To service the tuner module, the PCB has to come off its mounting tray. Once the twist tabs on the topside have been released, these red arrowed solder tabs need to be de-soldered. The board can then be separated from the tray.
This is what the board looks like without the tray. It is very, very likely that there will be more than a few bad solder joints here. I find that in general, bad solder joints are very common to these Mitsubishi built head units. I’ve even begun seeing them in the newer decks, like the popular CD/cassette combo unit from the mid to late 90s.
It’s at the point now where any time I have one that came from Mitsubishi’s factory, I automatically go through every single circuit board to look for bad joints.
Now, we can disconnect the blue arrowed cables to remove the faceplate PCB. But before we do that, a word or two about those other arrows.
Purple arrows indicate the cables that go down to the cassette module. Due to space issues, you may find it easier to disconnect these cables here, rather than at the cassette module itself. Keep notes on where everything goes, though with each connector being different from the others it’s not really possible to mix them up.
Green arrows show you the three screws that hold the mainboard from the chassis. We are a long way from removing those, yet. The mainboard is the last part that can be removed.
Here’s the faceplate PCB and its black plastic insulator plate. Don’t forget to put that plate back in. Make sure you shoot some contact cleaner at those equalizer controls, as well as the three green potentiometers on the fader joystick.
The illumination lamps on this unit are the usual 12 volt 3mm grain of wheat lamps in twist lock bases that were all the rage around this time. I’ve indicated them with green arrows. You can usually source replacements for these, as well as their blue filters, on eBay. They will not come with the twist lock bases... you must unwrap the lead wires from these bases and remove the lamps so that the bases can be re-used.
Our next step will be to remove the cassette module. Take the bottom cover off, and you will see this view. Red arrows indicate the screws holding in the whole assembly. Remove them, and then make sure the four cables denoted by yellow arrows are disconnected. Again, you may choose to disconnect some of them on the mainboard instead. Particularly if you have fingers as big as mine.
Blue arrows indicate the screws that hold the cassette module to the cassette tray. Don’t remove those yet... you only need to remove them if you are replacing the cassette belts.
The cassette module itself is pretty well the same one used in both the Infinity II and Infinity III, with a few minor changes. It is every bit as problematic. These tend to develop slop in the loading mechanism, causing the loading arm (red arrow) to fail to press hard enough on the switch indicated in blue. This causes the loading mechanism to cycle over and over without a cassette being present. I usually address this by bending the little tab that pushes the switch outward just a bit.
Regardless, this mechanism also suffers from the odd reel sensor failure as well, causing the deck to reverse direction over and over. When this happens, it’s over... you cannot replace the reel sensors. It’s best to find an identical parts deck at that point you can grab the whole cassette module from.
Once you remove the module tray, you can access the belts. This version of the cassette module is much easier to work on than the one found in the original Infinity II in that the red arrowed ribbon cable is attached via a friction fit connector this time. In the older deck, it was soldered down.
To replace the belts, just pull the cable out of the connector. Both belts are 1mm thick. I’ve measured internal circumference at 280mm for the big one that turns the capstans and 100mm for the small one that runs the reels. Deduct about 15% from the measurement of the long one to account for belt stretch, and you get a value of 238mm for a replacement. We’ll leave the smaller belt alone, as it is not stretched on my unit.
Now, we’re going to get into the mainboard area. To access it, remove the red arrowed screws and lift out the tray separating the board from the cassette module.
You may now address any bad solder joints on the mainboard - there is no need to remove it.
If, however, you do need to remove it, de-solder the three green arrowed tabs. Then, remove the three screws I showed you holding the board to the chassis.
Now, remove every single screw on the back panel and remove the back panel. With this out of the way, you can gently work the mainboard out of the chassis.
This is the mainboard with the chassis removed. There is no need to remove that big metal bracket to replace the amplifier chips... they can already be taken out as is. I will, however, remove the bracket so I can give you a look at one of those parts.
There are two amplifier chips in this deck, both Toshiba TA8221H parts. They can be found brand new on eBay at the time of this writing, are 2 ohm stable, and are good for about 15-19 watts into each of two channels at 4 ohms.
With the mainboard out, there’s only one thing left in the chassis: the volume/power control PCB. We’re going to remove that too, because when you’ve already come this far you might as well go all the way. It is just as likely that you will find bad solder joints on that little PCB as anywhere else in this deck, and it’s always a good idea to shoot some contact cleaner into that green potentiometer anyway.
Simply remove the nut that holds it to the housing, and it pulls right out.
The volume/power control board is really simple stuff, but don’t forget about it. While the potentiometer is pretty well sealed, it’s wise to clean it anyway. Look for small holes and cracks in the casing through which you can shoot the cleaner.
Now, it’s time to re-assemble the deck. Consult my pictures as needed to do so. It’s not quite the hardest deck to get apart that I’ve worked on... that honor goes to the Ultimate Sound deck from the mid-80s, also built by Mitsubishi. It is, however, enough to make one glad for the more simplistic head unit assemblies we get from Chrysler in the new century.
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