Radio/Stereo: CR-4024/CR-4123: The Definitive Thread

[Suterman]

Thanks for the reply, I already checked the fuses and they are fine. The frustating thing with this unit is it worked perfectly the last time it was installed and I only took it out because I wanted to play some CDs in the car. since then I have started using a smart phone and discovered the wonder of bluetooth so the CD player is now no longer required.

I'm not into electronics so I won't be going any further with this head unit, I've ordered a cheap replacement unit that has bluetooth and FM radio for £18! that will do for me and will plug in to the amplifier I have with no trouble.

[TheHungriestBadger]

Firstly, a quick thanks to Suterman for donating his unit to the cause, I have been able to delve further into the unit with slightly less concern about breaking 'the only one'.

The faceplate on these units is a single moulding (no separate bezel and/or fascia like with the CR-7xx or CR-9xx units). As a result, it can seem daunting to attempt to remove it, but the process is actually remarkably simple - the only items holding the unit captive are the power/volume knob and fade control ring, the tuning knob and band selection ring, and the cassette direction/eject switch. The removal process is detailed below:

1) If your unit has rubber end caps on the power/volume and tuning knobs (mine did, Suterman's did not) these are a simple press fit - albeit quite a tight one. To remove these, simply take a flathead screwdriver and pry under the lip of the rubber cap and away from the unit. You should be able to use the faceplate to lever against, but don't force it as it may cause damage.
2) With the end caps removed, now remove the plastic knobs that form the power/volume and tuning knobs. Again, these are a press fit, this time onto standard D-shaft switches/potentiometers. They are a rather tight fit, I opted to use a pair of needle-nose pliers. Grip the plastic knob firmly so as to prevent the pliers from slipping when pulling, but not so firmly as to crack the plastic (although the risk of this is low). Pull firmly, and squarely away from the unit.
3) Remove the fade control and band selection rings, these should simply slip off as they are held captive by the power/volume and tuning knobs which are now removed.
4) Remove the two low-profile nuts from the thread on the switches/potentiometers. To do this I again used a pair of needle-nose pliers to start the nut off (the switches are too deep for a socket, and the nut is recessed preventing use of a spanner). Once started, I used a flathead screwdriver to continue spinning the nut until it was off of the thread.
5) Remove the plastic cap on the cassette direction/eject switch. This was carried out in a way similar to step 2; needle-nose pliers, firm grip, pull squarely away from the unit. The actual method of attachment for this cap is an insert, similar to a spade terminal.
6) Pull the faceplate free, as per usual, pull squarely away from the unit. It should be completely free at this point, but do be wary in case it becomes snagged on the metal chassis. Do not force it at this stage, only apply gentle force if absolutely necessary.

Following this procedure, one should now have access to the PCB containing the VFD display, the station memory buttons, and a selection of bulbs. It should be worth noting that the cassette direction indicators (arrows) are actually formed (triangular) LEDs and NOT filament bulbs like all the others.

Finally, do NOT attempt to remove the display/button PCB. There are (at least) TWO flexible connectors to this board, one of which is on the bottom side of the main board, and one of which is sandwiched underneath the power/volume switch. Trying to simply pull this board and 'hinge' it down will snap the latter flexible connector. I am still working out further disassembly steps... It's bloody complicated and rammed full of stuff.

[TheHungriestBadger]

Removing the mainboard (the bottom PCB, as shown in the attached image) is not necessarily a complicated process, but it does require a degree of patience and a gentle hand. The process is outlined below.

In addition to these steps, one does need to have already completed "Removing The Top Plate" (post #7), "Removing The Bottom Plate" (post #8), and "Removing The Faceplate" (post #22).

1) Remove all the screws visible from the outside of the 'walls' of the chassis - the majority of these are located on the back of the unit; however, there are one or two on the sides as well. These will likely be seized (as are most screws on these units. Do not just try to brute force these screws, as they will just round out. Instead, apply a penetrating oil (I've used standard WD-40 and the straw nozzle) and allow it to soak in for 10-15 minutes. Then they should crack loose with a modest force applied. My tool of choice for a while now has been a small 1/8" ratchet with suitable adapters to take screwdriver bits.
2) Remove the L-shaped metal panel - presumably a heatsink - from the rear-left corner (when viewed from the bottom of the unit).
3) In my case, there was a small bulb (used for backlighting the cassette flap) hard-soldered by on the tuning-knob PCB) consisting of a green and red wire - see the attached image. This needs to be desoldered since the bulb itself is glued to the chassis.
4) Using a small flathead screwdriver, gently begin to lever up the mainboard from the side, it does not matter where you choose to pry from. One does not need to desolder the various angled 'tabs' (used for grounding to the chassis and mechanical support) since these connect to a 'second skin' of the chassis which comes away with the board.
5) Carefully lift the board up, whilst rotating it so that the components face upwards. You can then lay it down next to the other half of the unit. The two halves are connected to one another via a length of flexible PCB to the front PCB holding the VFD display; however, this is plenty long enough to provide sufficient slack to lay the two halves next to one another. Be careful though as these may become brittle with age, and the last thing you want to do is break one of the traces on this connector.
6) As a heads up in advance, the FM module and the tuning knob switch & PCB will come away with the main board - this is normal but may catch you out if unprepared for the fact.

Through tearing this unit apart, I am discovering that it is not nearly as intimidating and 'unserviceable' as I initially thought, it's just not at all obvious how it comes apart initially. The turning point was certainly removing the faceplate as discussed in my previous post.

Alternative Links:
https://drive.google.com/file/d/1dsU...usp=share_link
https://drive.google.com/file/d/1Btj...usp=share_link

[TheHungriestBadger]

My bad, I missed out some stages in the process of removing the mainboard in post #23, please follow these steps and consider that post superseded.

In order to carry out this work the following stages need to have been followed:

- "Removing The Top Plate" (post #7)
- "Removing The Bottom Plate" (post #8)
- "Removing The Faceplate" (post #22)

Once these steps are completed, the following must also be done:

1) Remove the 3 screws on the rear of the unit as shown in the attached photo.
2) Remove the metal retaining plate now exposed on the front of the unit. To do this, remove the two visible nuts from the power/volume switch, and the tuning switch. There is a possibility that you will also have two screws in each side of the unit - one of mine did, the other did not. If this is the case, these also need to be removed; the locations are also circled in the attached image. The retaining plate should now slide off straight away from the unit.
3) Remove the final two nuts on the switches, and also remove the silver screws (locations circled) on each side of the chassis.
4) Again, as an optional extra, your unit may or may not have the 'standard' metal spring clips, often found on units installed in 7/940s, despite the 240 not requiring such clips. If your unit does have them, they need to be removed. These are held in place with a single screw each. The location is not shown here, but it should be fairly obvious if your unit has these or not.
5) Desolder the two wires (likely green and white) from the PCB of the tuning-knob as shown in the attached image. This is because the tuning-knob and PCB are attached to the mainboard 'half' whereas the other end of these wires is attached to the other 'half'.
6) Finally, you should be able to pop the two halves apart by applying careful but firm pressure to the two points circled in the attached picture. These points are the top of the RF module (metal-shielded rectangle, oriented vertically), and the section of PCB by one of the faceplate backlighting bulbs at the front of the unit. Additionally, or alternatively, one may need to flip the unit over and use a small flathead screwdriver to pry up along the edge of the mainboard. This should be done with caution - if you encounter significant resistance and the mainboard is flexing instead of lifting out, stop immediately and double-check whether any additional screws are still holding the mainboard captive. Finally, it is worth noting that the mainboard is connected to the 'top half' by a flexible connector, the other end of which connects to the power/volume switch. This connector may become brittle with age, so take care when separating the halves, and try and pivot the unit around the left side (when viewed from the front) to avoid putting the connector under stress. There is enough slack on the connector to lay the two halves flat on a surface.

Apologies for having to make this correction, but hopefully this prevents damage to other units, and provides a more efficient method for removing the mainboard. It should be noted that simply removing the mainboard grants the user access to practically every aspect of the unit - the mainboard itself, the other PCBs in the 'top half', the cassette deck screws, and hence the auto-reverse board and tape-head board attached to it.

Alternative Links:
https://drive.google.com/file/d/1U8-...usp=share_link
https://drive.google.com/file/d/15I6...usp=share_link
https://drive.google.com/file/d/1DAI...usp=share_link
https://drive.google.com/file/d/1mqz...usp=share_link
https://drive.google.com/file/d/12-x...usp=share_link

[adammerve]

I just powered up the cr4024 in order to test the din outputs, it worked, then did not work and appears to have died.

Showbox jiofi.local.html tplinklogin

[TheHungriestBadger]

Define "appears to have died"? As in the display no longer powers on or anything? Whilst it is possible that probing the DIN outputs could cause unit failure, it is very unlikely, I mean, a human finger is far more 'dangerous' from the electronics' perspective than a DMM or oscilloscope - lower resistance and higher capacitance producing far more severe ESD (electrostatic discharge - essentially a static shock that can damage electronics before it becomes feelable to humans).

More likely it is just coincidence as these are old units now.

As an aside, if the display does still illuminate, try turning the volume to maximum - you may be able to hear audio very faintly, in which case the preamp might be 'nuked'. Having said that, you should still be able to hear the speakers 'pop' as the external amp gets turned on... I guess if not, then perhaps it's the control signal and/or associated circuitry that has failed.

Equally, it could be coincidence and simply a dry capacitor, corroded PCB trace, cracked solder joint, etc.

[TheHungriestBadger]

Against all conceivable odds, my friend has just purchased a Volvo 760GLE, and in the glovebox, in the book pack was the user manual for this lineup of stereos. I have since scanned this and converted it to a PDF. A compressed version is attached directly, but a higher-quality version is linked below.

Alternative Link:
https://drive.google.com/file/d/1Jhf...usp=share_link