Uher 4400 Report Stereo IC Checkout

[DMcMahon]

Before replacing the damaged wires I will sketch out all the numerous connections at and going to the battery box, also work out why there are 2 switches on the under side of the battery box. i.e. schematic only shows a single K5 switch.

David

[DMcMahon]

As per the schematic K5 is just a single switch, its bottom and top contact arms have 2 contacts each so on original brief look I thought it maybe was 2 separate switches.

K5 is normally open and it closes when a Uher rechargeable battery is fitted in the battery box and it connects the -ve battery contact out to pin 5 of the 6 pin DIN Accessories socket connector. Pin 5 is the charging supply from the Uher Z 124 / Z 124A / Z 124A1 power adaptor.

K5 is used in conjunction with K6 (normally closed), K6 connects the -ve supply from the Z 124 at pin 6 of the Accessories socket through to the battery -ve connection, i.e. same point K5 connects to.

K6 operates (opens) when DIN connector is plugged into the Accessories socket, this is to isolate the the Z 124 supply at pin 6 from connecting through to the battery box to isolate any fitted batteries or chargeable battery that may be fitted. Pin 6 also connects the Z 124 supply through to the main unit via K4.

I found that when DIN plug is plugged into the Accessories socket that K6 was not switching. K6 is mounted on a bracket directly above the right channel external speaker out 2 pin DIN socket and an operating lever from the switch goes across and enters a slot in the top of the Accessories socket.

The operating lever arm was sitting too high to be actuated when DIN plug was plugged in, found that K6 was sitting loose above its bracket, i.e. not fixed down. Removed K6 and found that it is riveted to the bracket but the rivets have parted company with the bracket.

I think this may explain why the battery box wires overheated etc If someone previously had either normal batteries or the rechargeable battery unit fitted and connected the Z 124 then K6 would not have isolated the batteries.

The problem now is to get K6 refitted, could try self tapping screws but I think the rivet holes through the K6 parts will be too small diameter for the screws to screw into the bracket. If not then maybe glue the switch down onto the bracket.

The Service manual has a set-up procedure for K6 which says to loosen the speaker DIN socket and adjust the switch bracket, this is nonsense because the bracket is glued to the case and not fitted to the speaker DIN so there is no adjustment possible.

David

[DMcMahon]

Originally Posted by DMcMahon

The Service manual has a set-up procedure for K6 which says to loosen the speaker DIN socket and adjust the switch bracket, this is nonsense because the bracket is glued to the case and not fitted to the speaker DIN so there is no adjustment possible.

David

After closer inspection see that the bracket has legs that extend down and are clamped to the case by the DIN socket securing screws. The legs have cut-outs so making the bracket height adjustable. The bracket was also firmly fixed to the case by either glue pads or double sided adhesive tape.

Had to prise the bracket off the case to try and fit some screws to re-secure the K6 switch but could not find any suitable screws either self tapping or nut and bolt so am attempting to superglue the switch back onto the bracket.

David

[DMcMahon]

Superglued the K6 switch to its mounting bracket and later tested its operation all OK.

Replaced the damaged wires on the battery box, powered up the battery box on its own and also meggered the wires all OK.

Powered up the unit without the battery box fitted using a more powerful PSU (30V at 2 amps), a very nice Farnell I got quite a while back through the Forum.

Retested the remote pause operation using the Uher microphone but it still does not work, the voltage now does not drop off and the current goes up to 800mA but relay A does not energise.

Pressing the Pause key (which lifts the Pause lever off relay A armature plate) allows the relay to energise.

As before it looks like the relay cannot move the pause lever up when remote pause is selected. This pause lever is quite strong with spring tension but do not know if it is abnormal or normal. I will check it on my other Uhers to see what they are like.

The pause lever disappears into the keys assembly block and it is just about impossible to see/access this area.

David

[DMcMahon]

Tested remote pause operation using the Uher microphone on my Uher 4200 Report Stereo and it worked all OK even when using the 500mA PSU.

Removed the battery box and speaker on the 4200 to compare relay A and the actuating remote pause lever, all looked the same as the 4400. The remote pause lever on the 4200 feels as strong as the 4400. One possible difference is that on the 4200 the lever does not contact the relay armature plate, it sits a couple of mm away from it (when Start/Play is selected) this means that the relay can start to energise and partially pull down the armature plate before it hits the strong resistance of the pause lever.

I thought on the 4400 that the lever makes contact with the armature plate when Start/Play is selected, so then not allowing the relay to energise mechanically unless it can overcome the strong lever pressure, I need to recheck this as it is very difficult to see.

Interesting the 4200 does not have a power supply PCB like the 4400 and the 4000 Report Monitor, the power supply components are mounted on the underside of the battery box, this makes it harder to access/remove the battery box due to tight cables etc.

David

[DMcMahon]

Recorded some stereo music on the 4200, which plays back well on the 4200 (external speaker connected to the right channel speaker DIN to be able to hear the right channel) to play the tape on the 4400 to see if the playback of a recording not working on the 4400 right channel is a Playback or a Record issue.

But after loading the tape onto the 4400, play mechanically is now not working at all on all 4 speeds.

Can see that the pinch wheel is moving to the rotating capstan shaft but not making enough contact to drive the tape, by manually pushing the pinch wheel assembly can get it working OK.

Strange that this should occur now. Need to check the pinch wheel pressure setting procedure, think I can see the adjustment, a metal piece that can slide on slots to adjust pressure on a spring, the 2 screws/nuts for this are well locktited.

David

[DMcMahon]

Checked the pinch wheel pressure setting and forward travel as per procedure in the service manual all ok. Could visually see that the pause lever was making hard contact with the armature plate of relay A and was stopping the pinch wheel was making full contact with the capstan shaft when Start was pressed.

The service manual has a procedure for the pause lever and actually shows the lever in Fig 9.

The lever (shown removed in first photo) is secured by 2 screws one of which has a slotted hole in the bracket so the arm can be swiveled.

After several iterations of adjustments got the pinch wheel to make proper contact with the capstan and also got remote pause working from the Uher microphone. It was quite a fine adjustment range, quite easy to adjust so that either remote pause did not work or pinch wheel would not contact fully the capstan or both.

Played the tape recorded on the 4200 and still no playback sound on the right channel (with external speaker connected) so need to have a close look at the playback amplifier.

David