More on the Super-rare Grundig SVR4004. A format of only one model. 

This is "just" cheer electro investigative drive, a rare sport... Must be praised for the patience, courage and honesty. When this early video machines were made, I'm sure no one would ever think that 40+ years later, a clever brit would diving into German junk like this. Someone's footage on that rare vintage format, will be thankful, when brought back to existence and digitized to "eternity". Video empowers people! Cheers 📼

Despite me not having time to watch this from start to finish, thank you for filming it!

I've had sooo many cascading faults with dipped tantalums that at this point, if the unit is 30 or more years old, I start with replacing all of them before even attempting a power up. If it's a DC rail decoupling cap, I replace it with a low-ESR electrolytic, if it's a low value coupling capacitor in the signal path, I use a film capacitor. SMD tantalums last longer because their epoxy coating is much thicker. I have two NOS video waveform monitors, when I powered one up, a dipped tantalum smoked. It was on the 5v rail, I've cut it out. Then the next one smoked, rinse and repeat ~15 times. When all the tantalums were removed from the 5V rail, the unit started working. For about a minute, then an other tantalum, this time on the 15V rail shorted out. I haven't powered up the other one, as I want to make a video about it. It will probably be a smoke machine just like the other one. And they are not even that old, from 91 or 92 IIRC, and the tantalums are KEMET or some other good brand, rated 16V on a 5V rail. They were stored in a damp basement, their cardboard boxes are moldy, so their aging was accelerated. One of the big enemies of tantalums is moisture, it slowly gets through the thin epoxy coating. The other enemy is oxygen, which also penetrates through the coating. Hermetically sealed metal can tantalums on the other hand, are everlasting, as long as they are protected from voltage surges.

Your videos are great, I love anything video, and remember agonising over beta or vhs. back in the day. I wish I understood the technicalities, but a little too long in the tooth to learn now!

Perseverance will always win rewards, great content

There are still many blue tantalum capacitors and FRAKO electrolytic capacitors in the device.

thank you for the video. thank you for showing how precise one can chase a fault which turns out to be a working component. it is part of the process and not giving up to easy. the desintegrating plastic parts are a real pain with some manufacturers products. others might say they were not so as long as the company expected this machine be of use for anybody but you repairing and using this prooves these voices being wrong.

Thank you Colin tricky repair,

Max Grundig wanted this format to be built, so it was built. Market analysis did not matter to him, he followed his "stomach" feeling. Much to the disadvantage of the company.

Wow, what a trip! Yeah those 723s are always a pain in the arse... when you show it the first time on the diagram I was like noooooo... a 723 😅 But it's strange why something was smoking, on the top part of the circuit there is an "electronic fuse" which through that SCR disables the output in case of overcurrent - at least, it should do that...🙄 So basically we had a dead 723 to begin with, and then that tantalum got shocked when it saw again some electrons after who knows how many years of total darkness 🤣And now something else gave up again. Maybe another tantalum had enough? 🙄 Can't wait the next episode 😅

I have a printed original version of the service manual with an appendix. Grundig changed the pinout ofB1 and B4 during production. They turned it around. 1 is now 10 and 10 is 1. In the sve 4004el there is another schematic of the power supply.

Great video Colin, I love these in depth videos about real vintage technology. You have a lot of patience! You’ve inspired me to take another look at my machine (when I have a lot of spare time). The main fault on mine is that the capstan pinch wheel solenoid doesn’t engage in play. Any ideas which voltage might be missing? Cheers, Rob.

40:03 I hate to throw a wrench into your troubleshooting, but there should not have been any smoke escaping at this point. The 15V regulator is protected by a feature called electronic fuse "ELEKTRONISCHE SICHERUNG". And this electronic fuse is build around the thyristor/scr TY447 2N5081G. And this protection works as follows; TY447 monitors the voltage drop across the resistor R451 (0R22). If the output current rises the voltage drop across R451 increases. If that voltage across R451 exceeds the Gate to Cathode trigger voltage of TY447, the SCR conducts and puts a positive voltage from the raw 22,6V line via R443 onto the node of R446/R447 and thus effectively pulling pin 2 of the uA723 high. As a result the uA723 has to immediately switch off any base drive to the pass transistor T449, and the whole 15V output will shut down. The cleverness with this circuit is that it latches the supply in the shut off mode and will not let it come back up, even if the short disappears. Why is that so? Because like any thyristor SCR TY447 will stay conductive as long as it has any Anode to Cathode current flowing through it, even if the Gate drive (hence excessive output current thru R451) disappears. As a result after an overcurrent trigger event, the pin 2 on the uA723 will stay pulled high and the 15V supply will stay shut down until the whole VCR is fully power cycled. I wonder where we did see this behavior... Oh right, the previous Grundig SVR 4004 did exactly behave like that; the 15V line IMMEDIATELY shut down on the overload caused by the bad tantalum and stayed shut down until a power cycle. What this means for this VCR is, that either this powersupply board is a different revision missing this electronic fuse feature (I hardly think so), or the SCR TY447 is bad or was disabled by a previous tech troubleshooting, or the "NEW" uA723 that you fitted does not handle the signal to pin 2 correctly, meaning it is a fake. The latter can be proven easily by upon proper operation passing voltage from the 22,6V rail thru a 1,5k resistor into the node of R446 and R447, and watching if the 15V line shuts down. Whatever you do, Bottomline is; The 7V you saw on the 15V rail before the smoke escaped should never have happened. The overload shutdown should have kicked in instantly and lasted until cycling the power. Just like seen on the previous 4004. Seeing how these VCR are prone to problems with tentalums on the 15 Volt line shorting out, I strongly suggest investigating into why this powersupply did not shut down the 15V rail on overload properly, unless you want to fit a fuse in the 22,6V rail to make up for that protection feature not working. Side note; Why didn't you use a current limited(!!!) bench powersupply to externally feed the 15V rail? You could have easily seen how much current was drawn and which module was the culprit.

B4: 1. Permanent -26 V 2. GND 3. 4. Motor Control Board 13 (I assume pin 13) 5. Locating hole 6. To clock 9 7. Permanent +12 V 8. Syscon board 23 9. IF fine tuning +15 V R - active when the machine is on and a function key has been pressed, relay is latched +15 V E - active when the machine is powered on but idle

Your ability to trace the faults is very impressive.

That one was a bummur..but, you WILL fix it, no doubt about it. Excellent stuff.

More Video 2000, please?

Thanks for another excellent repair video. I remember a mate of mine had one on the 1970s?

Bloody Tanty's. (and light bulbs. ha ha)

I wanna see you working on a shotgun microphones, specially Sennheiser, thanks for your patience

wow i never saw it in my short life...look this mechanics 4 heavy driver motors two big motors must be drum and capstan others one must be reel and loading

Are you going to put that in the obselete junk museum? 🤔