Uher 724L

[David001]

Hello.

I obtained this, nothing works, no light, no hum. Upon opening the back, saw this rather badly corroded fuse and fuse holder. Would this be a likely culprit? Ordered 2x 0.3A 5mm by 20mm ones online. From what I could tell, no components like big capacitors seemed blown, no funny smells or such. Everything looked in good condition inside.

I also cleaned the heads. Oddly, it comes with (fell out as I turned it over) a plastic 'trick' key, which apparently lets you do overdubs? Anyone tried this?

I only do playback of old tapes at various speeds, record loops and similar, not really a competent repair guy. It took ages to work out the way to remove the top*, tbh.

Any help/advice appreciated. Thanks!

*safely, without damaging it, of course

(I have other Uher R2R, but 5", no 7")

[DMcMahon]

Hello David,

I am not familiar with the 724L but I have several Uher Royal de Luxe which are somewhat similar.

In my experience it is not uncommon for the metal end caps of the glass fuses to be corroded with a blue/green battery type looking corrosion, maybe a form of Verdigris, across many vintage recorders.

Generally it does not cause a problem (assuming the fuse has not actually blown or the corroded fuse holder has not lost spring tension) although I always replace fuses that are corroded to be on the safe side and also for cosmetic appearance.

The fuse in your second photo appears to be the mains voltage fuse that protects the mains transformer, on the Royal de Luxe models this fuse is fitted in a fuse holder in the rear panel.

There will be a second internal fuse that is connected between the mains transformer output and the bridge rectifier, the circuit diagram shows it to be 0.7 Amps, so you should look for that as well. This fuse is fitted to the power supply board.

Cannot fully tell from your second photo, but is the mains voltage rotary selection switch correctly set to 240 volts ? I assume you will have checked the mains fuse in the 3 pin plug.

On the 724L I do not know what control switches power on, but on the Royal de Luxe you do not get power until one of the tape speeds is selected.

Not familiar with the plastic trick key.

Regards

David

[DMcMahon]

I think the power supply board is the item shown near the top left corner in the attached Word file, there will be 3 diodes, 3 resistors and at least 8 capacitors on it as well as the fuse holder.

[David001]

Thanks! I think the fuse has blown, both ends were severely pitted and discoloured.

I'll try and look for the other fuse tomorrow, will see how it goes.

Much appreciated

How do I check it's at 240V- is there an index mark? It had a European 2-pin plug, changed for a 3 pin. Bought it as untested

PS. Saw your Grundig thread, very interesting. Did they make any two-speed ones?

[DMcMahon]

I have several Grundig threads, they can be 1, 2, 3 or 4 speeds depending upon model.

[DMcMahon]

Attached is Royal de Luxe photo showing 240 volts setting, you will see 240 is next to a cut out notch, i.e. you rotate the switch until 240 aligns with cut-out, so maybe yours will have something similar.

If it came from the continent then most likely would have been set to 220 volts.

I was incorrect in saying that the mains fuse was on the rear cover on the Royal de Luxe, should have said on the rear side accessible from the rear cover.

[David001]

Hello- here are two pics from the Uher 4000 Report Monitor I mentioned, plus two pics of the 724L. The voltage selector seems correct

[DMcMahon]

You probably should create a new separate post to cover the Uher 4000 issue, there are many Uher 4000 owners in the Forum.

[David001]

Yes, although I suppose I'll just need to wait till the pandemic is over to find a repairman.

[David001]

Here is a pic of the 'trick key'. You slide it into the tape slot under the second rise of the capital U on the faceplate, it covers the erase head, and you can do sound on sound.

It's made of flexible plastic, about 1mm thick.

[ricard]

Interesting about that 'trick key'. I've seen machines that have a mechanical lever which lift the tape away from the erase head when activated. It doesn't seem to have been a common feature though. Some machines do it (e.g. Grundig TK54) by having a trick button which basically turns of the current to the erase head, which of course does the same thing.

At any rate, the original recording still gets partly erased by the recording bias, so in my opinion the whole function is of questionable value, although of course it is very cheap to implement so obviously considered worth a go by some manufacturers.

[David001]

Update: fuses arrived, and it works, apart from rewind. Sadly, there's no sound output from speaker or line out. That's going to be for a repair man, I think.

[DMcMahon]

That is a great shame.

Is the power indicator lighting ? this would indicate that the second internal fuse is OK.

[DMcMahon]

If the power lamp is lit, then the 2nd fuse should be good. If you have a meter then the first thing I would do is make sure the 3 DC voltage supplies are good, measuring at power supply board previously referenced, across 3 electrolytic capacitors namely:-

C52 (2,000uF) - Should be around 17 vdc
C47 (500uF) - Should be around 16.5 vdc
C37 (500uF) - Should be around 35 vdc

[DMcMahon]

Rewind not working is most likely mechanical, idler wheel contact possibly.

[DMcMahon]

Have emailed the 724L Service manual & Spares listing. Also old Uher catalogue showing the 724 but maybe not the Stereo L version.

[David001]

Haven't found the second fuse yet, will need to take a look

[David001]

No lights either, sadly

[DMcMahon]

That may be good indicating that the second fuse has blown, maybe what is not so good is what would have taken out 2 fuses !

Just realised that I emailed 2 copies of the Uher catalogue instead of 1 copy and the Service manual, but now see that the Service manual is far too large to email !

Second fuse maybe is 60mA, difficult to read on schematic.

[DMcMahon]

Ignore 60mA fuse reference, now think it looks like 0.8A possibly.