Grundig TK 745 Evaluation

[Refugee]

Have another look at that black clip you showed in post#2 and see if it is supposed to push the FF wheel a little bit further if fitted there.

[DMcMahon]

Yes have regularly been trying to find a home for it. Most likely looking suspect area was the switch pushbutton assembly (because all the fittings there were black plastic and had initially encountered some issues with the pushbutton mechanics) but it did not go there.

At this stage I do not think it is anything to do with the FFD drive. When FFD is selected it is moving to its maximum stroke, even if I push/pull hard on the mechanism there is no movement at all so it looks like it will not be possible to gain anything there, That then just leaves the rubber idler wheel.

When I get it all powered up with tape running will have another closer look.

[DMcMahon]

After numerous attempts failed to get the power On/Off mechanism working properly, then at one stage a small piece of plastic broke away from the black plastic On/Off push button.

This little plastic piece is the outside wall of a small entry area where a prong on the metal actuator fits into. After this still no joy getting it to work. Then noticed that the metal actuator prong was slightly bent/twisted, so I straightened it.

Directly after this and refitting the actuator, the mechanism then worked fine, whether it was the bent prong or just pure luck I do not know.

Seems to be working fine with the missing/broken plastic side wall piece, could try gluing it back, but doubt that the repair would last long and to remove the On/Off push button would require lifting up the heads assembly, which unless really necessary I do not want to do, as there are sprung loaded wire actuator mechanisms connected to/below the heads top plate that are best left undisturbed.

Tested Playback, works really well and sounds very good especially in stereo, getting both channels now, on original attempt only got 1 channel.

Had a look at FFD not working again. The rubber idler that drives the Take Up Reel Table was not only not making contact with the table but also not making contact with the driving wheel (I previously called this driving wheel "mini flywheel").

With a lot of force could pull/push the metal actuator arm assembly (that the rubber idler connects to) so that the idler wheel would make contact with the driving heel and the reel table and then get good FFD all the time I held the actuator in that position.

For reasons unknown I then tried pulling up the actuator by holding a narrow (1mm) vertical strip of metal (can see it in the first photo directly below the rubber idler, looks like it is touching at 6 O'clock) using a pair of long nosed pliers. It did not appear to move but ever since FFD is now working very well !

Next is to refit the VU meter, during unit dis-assembly it basically fell apart, then refit the top panel and test recording and soak test Playback/RWD/FFD.

[DMcMahon]

Found the home for the mystery black plastic part in Post 2, it belongs at the top left corner of the top panel, shown fitted in first photo, it does not seem to provide any useful purpose. Discovered where it belonged when I saw the identical part at the top right corner.

The top left corner obviously has had a knock, the metal trim is dented and loose, will try gluing later, also there is a little piece of black plastic at that corner that is also broken, maybe one of the several I pieces I found originally.

A bigger chuck is broken off at the bottom right corner, I think one of the larger broken pieces I found originally may fit or fit most of it.

[DMcMahon]

Originally Posted by 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.

After a few attempts at refitting the top cover, I am now up to speed with the technique of "click back into their grooves".

[DMcMahon]

Prior to re-assembling, replaced the burnt R566 with a new 1.2kohm and replaced the incorrect D504 with correct BAY 93. Retested associated DC supplies all OK.

Did glue repairs to broken plastic pieces on top panel and also to 2 broken off tabs on VU meter surround.

Tested recording (then playback afterwards) this morning, it worked very well on Automatic music and Manual recording modes. This machine only has a single recording level control (a shame) used during manual recording, which adjusts both channels.

So far have only tested the Diode line inputs, on pins 1 and 4, still to check Phono 1 & Phono 2 line inputs on pins 3 & 5. For the Diode input used a DIN cable with 470kohm attenuating resistors (in each channel) as often find with unattenuated cables that Hi-Fi phono line outputs are too strong for some DIN inputs.

Even though recording worked well, could not get the VU meter to work/indicate anything. This machine only has single VU meter where the 2 channels are combined for the meter output.

The VU meter also does not work in Playback but not 100% sure if it is supposed to work in Playback, there is one very brief reference to it working in Playback in the User manual.

So now need to do some monitoring to determine if the VU meter itself is defective or the electronics driving the meter. The electronics for the meter are on one of the tiny daughter boards that are mounted off the main board, could be difficult to monitor easily.

Have not yet tried microphone recording, the microphone input is an 8 pin DIN, not sure if a normal 3 or 5 pin microphone DIN will plug in.

[DMcMahon]

The meter electronics are good, the VU meter is dead. Wil be very difficult to find a compatible meter that will fit the VU enclosure.

3 pin microphone DIN fitted and microphone recording tested good on that left channel.

[DMcMahon]

While doing some more recording tests, the On/Off button locked up solid, found that its metal actuator arm had come out of the damaged pocket in the plastic On/Off button as per Post 43.

So tried to repair it, could not find the small piece of broken off plastic so have glued on a couple of short bits of ty-wrap, will refit and see how long that repair lasts.

[DMcMahon]

Refitted the repaired On/Off button and re-assembled everything. Tested headphone output all good, luckily I have a 5 pin Domino to 3.5mm adapter.(the 745 having a 5 pin Domino DIN headphones socket). Tested the Domino adapter in both of its 180 degree positions, one leaving the speakers in circuit and the other disconnecting the speakers.

Also tested both channels microphone recording using a Grundig GDM 314, which is a mono mic but has its higher impedance output (565 ohms) wired to both of the stereo mic pins 1 and 4. The mic also has low impedance output (12 ohms) wired to pin 3. In the 745 pin 3 is not wired.

So all the main basic functions are now working well, apart from dead VU meter.

Sometime later if I get time will have a look at the Special Effects like Echo/Multiplay/Duo/Synchro recording and mixing etc although not really interested in many of those modes.