Grundig TK 745 Evaluation

[DMcMahon]

Just having a quick look at another recent acquisition a Grundig TK 745.

It is a mid to late 70's solid state stereo, 3 speed, with internal power amps and speakers. It is rather lightweight and very plastic.

It was sold as fully working, but before shipping the seller said I could cancel my purchase because on retesting it, he had found that Play was no longer working. I decided to take the risk and go ahead with it.

It powers up and RWD works but Play & FFD do not work at all. I operated several of the buttons/switches including the Record button and this button now is permanently stuck down. Also one of the slide switches when I operated it made a sound as if something had fallen off it.

Shaking the unit it sounds like there are several pieces rattling around inside it !! So need to open it up and investigate further.

[DMcMahon]

Opened it up and numerous bits of plastic fell out. 4 or 5 I think are just broken bits of the casing, so not important, but 2 bits look like they belong somewhere (so could be important) but not easy to determine where.

Loads of very delicate looking mechanisms, some with fragile looking plastic actuators will have to tread carefully.

Have not been able to free the locked down Record push button switch, may have to remove the complete multi push button switch assembly, which does not look easy at all.

Think I can see why FFD is not working, the lever that pushes an idler wheel against the Take Up reel table is not moving up enough/pushing with enough force, reason currently unknown.

I can see that Play is not working because the pressure/pinch roller assembly is not moving to the capstans shaft, I can manually drive it over and it will then play and get good playback sound (but only on 1 channel) looks like 2 separate reasons, one is that sprung loaded multi lever mechanism is stiff and the other is that another multi lever assembly does not always push against the previous multi lever assembly (maybe not always aligning correctly). Very difficult to see as many parts covered under other metalwork. I think it is going to need quite a strip down to investigate further.

[Refugee]

I would save all of those bits of plastic until you have established that they have not come from important places.

[DMcMahon]

Yes will retain all the found plastic bits, hopefully will find home for the 2 pieces that look like they must belong somewhere.

[Ted Kendall]

Makes you yearn for the good old Reporter decks...

[DMcMahon]

I was close to getting a Reporter 700L recently. I doubt that there would have many/any delicate plastic parts

[DMcMahon]

Cleaned and lubricated 2 badly gummed up shafts for 2 of the operating linkages for Play, they are working well now and if I manually operate the control solenoid then Play works well.

But when the solenoid is electrically operated by the Play switch , 9 times out of 10 a white plastic actuator arm that the solenoid moves somehow is missing the end of the black metal arm (second photo). It is hard to understand how this can happen as when I manually operate it I cannot get it miss the black arm ??

Impossible to see the interface between the ends of the white and black actuator arms as under metalwork and the capstan flywheel also partially covers that area. so I think the only way to see more is to remove the flywheel, that in itself is not difficult but the metalwork attached to the flywheel has several sprung operated mechanisms which look like could be tricky, would rather not disturb but have no choice.

The Play switch itself now is also playing up, often not working, it is not a simple switch and it is difficult to see what it actually does, so as part of the Record switch being stuck down investigation probably will have to strip apart the multi-switch assembly which looks really not easy, to investigate both switch problems.

[Refugee]

Those two plastic bits do look like push rod guides.
You may well be closing in on the location of one of them.

[DMcMahon]

It is a real shame that Grundig virtually never did detailed exploded views of the mechanical assemblies like some R2R manufacturers did, then at least you could get a rough idea of where a mysterious part might belong.

[ms660]

The pics are a bit dark but if it's any use there's some more mechanical bit descriptions in here....once downloaded open up the spares PDF:

https://elektrotanya.com/grundig_tk7.../download.html

So far as I can make out from the schematic the start switch (play) connects the high power winding of the solenoid across the +A supply, and when the plunger is home the low power (holding) winding is connected in series with it, eg: the two windings are then in series across the +A supply.

Lawrence.

[DMcMahon]

Thank you very much for that Lawrence. I had previously downloaded it and saw that the Service manual was different to the other commonly found 745 Service manual.

But somehow I had completely missed the Spares listing file with its very useful mechanical drawings, so should be very handy indeed !

David

[DMcMahon]

After some tricky dis-assembling have nearly got the flywheel out (to be able hopefully see why the play mechanism is not working correctly when play solenoid is powered) but have hit a small brick wall.

Currently cannot remove the flywheel because a bracket that holds a mechanism for a small drive wheel (that drives the flywheel) is fouling the flywheel (when I try and lift it upwards) & currently cannot see how to remove the bracket assembly.

While disconnecting parts I found that the white circular mystery part in photo a few posts back, must just be a cable clip, because there are identical (but larger versions) holding down some of the cable harnesses to the chassis. So that is one part that I do not have to worry about, now know not an important part.

While disconnecting, saw a resistor that looks rather cooked, it is R566 a 1.2kohm according to schematic (have not measured it yet), looks like it might have been replaced before. It is on the output of the power supply bridge rectifier and connects to Zener diode D505. Will check this out (and check adjacent Frako electrolytic) once I have sorted the current mechanical issue.

[Techman]

Ah-Ha! I've got one of these brand new in the box

The mechanism is solenoid operated as far as I remember.

Original purchase receipt May 1976 as shown. They're a good recorder when working!

I've got a number of Grundig recorders in the collection.

[DMcMahon]

With mine in many bits and several issues to resolve, I am envious (in a good way) of yours !

[DMcMahon]

After trying various things and not progressing, resorted to a bit of brute force and managed to get the flywheel to lift out past the bracket.

Now I can see that as well as the white plastic actuator moving down when solenoid is energised (to actuate the various play linkages) that the white actuator can also slide sideways moved by a black plastic actuator arm connected to the multi-switch assembly.

Not 100% sure yet but think the black actuator arm is moved in FFD & RWD and this then moves the white actuator along sideways somewhat so it then does not actuate the play linkages when the solenoid is energised.

If this is correct then Play not working appears to be due to the white actuator being moved to the wrong position. This seems to be pointing to the multi-switch area operation again like the Remote button stuck down and the Play button not always operating the solenoid.

To prove all this first need to reconnect various disconnected cables including mains power cabling and power up (without flywheel and other parts fitted) and retest and see what happens to the white and black actuators when Play is pressed.

[Techman]

I've got a confession - although my recorder shown is still relatively mint in the original box, the reality is that it's actually had hundreds of hours use. I obtained it from its original owner sometime around 77-78 when it was just a few months out of warranty.

The only problems that have shown up over the years were minor mechanical adjustments involving, from memory, bending 'tabs' for drive and brake adjustments, and high resistance in chassis grounding connections through interconnecting plugs and sockets causing strange volume control faults, but that was only relatively (last decade) recently.

I would suspect that yours has received a bit of an 'impact' at some time by the look of what's happened.

[DMcMahon]

Think I have located the remaining reason why the playback actuator linkages are not working properly.

The black plastic actuator for FFD/RWD is very tight on its pivot pin (assume gummed up due to dried oil/grease + dirt on the tiny pivot pin shaft). This results in the actuator not being pulled back properly by a tension spring that is connected further along the chain, after a Play/FFD/RWD operation is stopped.

In Play this can mean that when the solenoid is energised the plastic actuator that is pulled down to subsequently through other linkages move the pinch roller forward, results in no movement of the pinch roller assembly because the actuator has missed (not in correct alignment) the actuator it is supposed to be pushing down.

Additionally the FFD/RWD black actuator is sitting slightly askew to the underside of the multi-switch assembly, due to its mounting bracket being slightly twisted, can see this in the photos.

This sometimes results in the actuator getting stuck as its travels past its stop and then get very intermittent/erratic operations until the actuator stop gets back in correct position.

I will remove the black actuator and straighten the bracket (too risky trying to straighten with the plastic actuator fitted) and clean/lubricate the pin.

While looking at this also discovered that the metal actuators for FFD & RWD that are also actuated when the solenoid energises, are also very tight on their pivot pins. So will remove the metal actuators and clean and lubricate the pins.

Could probably loosen up the stiff actuators with IPA followed by lubrication
without removing them but think best to remove for thorough cleaning.

I am hoping but not very confident that the stiff FFD actuator maybe a contributing factor to FFD not working.

To get all these actuators off their pivot pins you have to first remove the small circlip, even though generally this type of circlip is not in a circlip groove, I often find they can be very difficult to remove and replace.

For this very reason last year I purchased some very small circlip removal pliers, which turned out to be useless, because the width across their jaw pins is larger than the circlip distance.

From the underside of the multi-switch assembly was able to free the locked down record button. But find that when the button is pressed it latches closed in the down position (this maybe is correct) and when Stop is pressed the latch is removed but the record button does not release until pressed from the underside, it feels like the button mechanics are either stiff or catching on something.

It is virtually impossible to see what is actually happening mechanically with the switch mechanisms inside the multi-switch assembly. There is a coil assembly near the Play/Record switch end, removing this might enable a partial view of the Record switch and the troublesome Play switch mechanics.

Also spotted that there is a small problem with the Pause switch, it does not latch down, can see that a hole in its sprung loaded latching mechanism is worn/damaged resulting in a pin on the pause switch mechanism not going into the hole and latching the switch, with manual help can get it to latch.
So need to try and remedy this as well.

[DMcMahon]

Having quite a struggle with this. Could not remove the black plastic actuator for FFD/RWD in situ, so just cleaned/lubricated the best I could, this freed up the actuator on its pivot pin. But then saw that the bottom of the actuator sometimes was fouling a metal cut-out (for it to enter when he actuator moves between Play/FWD/RWD), can see no way of improving this apart from filing the metal to get a deeper/lower edge.

Straightened the twisted bracket for the FFD/RWD actuator.

Fixed the Record switch getting stuck down in Record position, found that a plastic actuator arm from the multi-switch assembly was not engaging into a small cut-out hole in a metal actuator that drives I assume the Record switch at the amplifier board.

Fixed the Pause switch not latching down by a bit of reshaping of damaged/worn hole in metal latching plate.

While investigating why the Play switch was no longer mechanical working it started working again, about the same time the FFD & RWD switches jammed up totally !

Have now after a quite a struggle removed the multi-switch assembly, of course now it is out, it will not go wrong (after loads of exercising it), difficult to see/determine how it could jam up and how the Play switch could stop working.

Plan to lightly grease the various plastic moving parts of the switch assembly.

Then refit it and test mechanically and then electrically, then refit everything else (not looking forward to that as some very awkward bits).

[DMcMahon]

As a bit of light relief decided to check out the burnt looking resistor R566. It measures fine at 1.2kohms

Probably would have been OK but decided to replace it for future reliability, because it has been stressed.

Unsoldered one end and a section of the artwork track lifted and broke off. I will be able to solder a connection onto the remaining bit of artwork track, but it looks like there is a plated through hole connecting through to artwork on the underside of the amplifier board.

Looks very unlikely that will be able to get a soldered connection to the top side of the plated through hole, so probably will have to remove the board completely to get access to the underside to replace the resistor and do artwork connection repair. Looks like it could a pain due to numerous metal actuating levers for the various slide switches on the board will need to be separated, but may have no choice.

Will get back to this later once I have resolved the mechanical issues.

[Techman]

You probably should have left that resistor alone, depending on how discoloured it looked of course

It's been a while since I looked at mine, but I think the record button stays down once pressed.

Your machine has definitely had a bad bash causing things to not line up as they should. Perhaps the chap dropped it as he was packing it, hence having to tell you that it now wouldn't work properly. I think you did the right thing getting it anyway, as they don't come up very often. The heads seem to last forever with no noticeable deterioration in sound over the years.

When you refit the top cover you'll notice that the sliders will have to 'click' back into their grooves - if you know what I mean.

The volume slider pots are a special type with a loudness tap, so completely unobtainable I would think. I was pleased to find the grounding issue with mine, as at first I thought it was an open circuit at one end of the potentiometer unit itself.