Hello everybody. I hope i posted in the right forum section. Recently moved to Germany and i bought this system a few days ago which i wanted to own since i was i kid, my uncle had the same one and i used to go at his house and listen to music on it. Bought it from an older man who agreed to bring it to the house i live in, there are also a pair of speakers going together with it. He told me that the system works perfeclty but i didn't test it in front of him because the speakers haven't got DIN connectors on them. So i bought connectors, connect the system, and it turned out that it has quite a few problems.
1. There is a problem with the Left channel, on both outputs (speakers A and B) the sound is not constant, it’s like trembling and rumbling, and when I turn the volume all the way down, it gives a sound like cracking, kind of like damaged vinyl. The Right channel works pefrectly.
2. Radio transmittion cuts out and gets right back (like sound-shhh-sound). Also when I listen through the AUX (TB) input, the sound cuts off completely and after a few seconds comes again.
3. Muting option when off, switches on by itself, but doesn’t mute the sound just while searching for radio station cuts the sound, and gets back when radio station is found. After some time the sound mutes completely, the mute indicator stays on all the time, and I’m unable to turn it off.
4. The turntables speed change button doesn’t work, the speed change is pretty mechanical, a mechanisam pushes the belt down to a bigger spinning area which creates more rpm. Maybe loose belt is the problem?
5. When I turn on the tape teck Left VU meter goes way up, and Right VU meter goes way down, but there is no buzzing or some noise.
6. Sometimes when I turn on the system, only when I’m touching the metal parts with the back of my hand I can feel slight electricity, but not all the time.
I don’t have any vinyls or cassettes here with me and I’m unable to tested the tape deck and the turntable, but the mechanisam of the deck works and spins, the turntable turns and I tried on the turntable when I gently touch the needle with my finger it gives sound.
The system is a bit dusty but in very good cosmetical condition.
I will post some pictures and videos of the system and its defects, sorry for the bad quality. Any advice will be much appreciated.
Youtube videos:
Grundig RPC 450 Left Ch. and Sound Defect
Grundig RPC 450 Tuner Defect
Grundig RPC 450 Tape deck VU Meters Defect
1. There is a problem with the Left channel, on both outputs (speakers A and B) the sound is not constant, it’s like trembling and rumbling, and when I turn the volume all the way down, it gives a sound like cracking, kind of like damaged vinyl. The Right channel works pefrectly.
2. Radio transmittion cuts out and gets right back (like sound-shhh-sound). Also when I listen through the AUX (TB) input, the sound cuts off completely and after a few seconds comes again.
3. Muting option when off, switches on by itself, but doesn’t mute the sound just while searching for radio station cuts the sound, and gets back when radio station is found. After some time the sound mutes completely, the mute indicator stays on all the time, and I’m unable to turn it off.
4. The turntables speed change button doesn’t work, the speed change is pretty mechanical, a mechanisam pushes the belt down to a bigger spinning area which creates more rpm. Maybe loose belt is the problem?
5. When I turn on the tape teck Left VU meter goes way up, and Right VU meter goes way down, but there is no buzzing or some noise.
6. Sometimes when I turn on the system, only when I’m touching the metal parts with the back of my hand I can feel slight electricity, but not all the time.
I don’t have any vinyls or cassettes here with me and I’m unable to tested the tape deck and the turntable, but the mechanisam of the deck works and spins, the turntable turns and I tried on the turntable when I gently touch the needle with my finger it gives sound.
The system is a bit dusty but in very good cosmetical condition.
I will post some pictures and videos of the system and its defects, sorry for the bad quality. Any advice will be much appreciated.
Youtube videos:
Grundig RPC 450 Left Ch. and Sound Defect
Grundig RPC 450 Tuner Defect
Grundig RPC 450 Tape deck VU Meters Defect
Here's the service manual to your Dual 1239A turntable. Yes, I agree with you, the belt needs to be replaced. It's available from many sources, e.g. Thakker.eu - Top Produkte zu Top Preisen.
The console' SM is available from Elektrotanya.
Best regards!
The console' SM is available from Elektrotanya.
Best regards!
Thanks for the replay and sorry for my late response. I got the system fixed, I found another device for spare parts who was dissassembled due to power supply problems, and luckly my devices power supply turned out to be fine. Everything is working perfectly, both channels and the sound is excellent, especially from vinyl, I bought a new stylus (JICO) and new belt but I have trouble changing the belt the plate is not coming out and since I'm not experienced in changing the belt I will bring the TT to expert to replace the old belt. The radio reception is excellent. I also got my computer connceted on the Line input. Here are some photos from the inside of the system from the defective boards, the functional ones I have in the system were much cleaner and looked like brand new.
Do you mean the TT platter doesn't come off? Lift the rubber mat a bit so you can see one of the two big holes in the cast metal. First rotate the platter until the hole is next to the rpm selector. Lift the belt from the motor pulley. Then rotate the platter 'til this hole is in the 4 to 5 o'clock position. You'll see a shiny bar that acts as a latch. Gently move this bar away from the center and the platter will come off. See also the relevant page in the service manual.
Best regards!
Best regards!
Thank you very much for the instructions. I successfully changed the belt. Now the speed change and the ptich control are working perfectly. I also have a Sony HMK-70 system back in my country and I also had trobule removing the platter from the turntable, maybe it's the similar procedure like on the Duals. I also ordered new stylus and new belt for the Sonys turntable, it is a Sony TTS-360 with Sony VL-30G cartridge. Best regards.
Thanks for the comment. I actually wanted to ask about recapping the system, or maybe improving the sound if possible (more wpc, less thd, etc.), or it will be better to leave it as it is? The pictures I posted are from the defective boards, I will post some pictures from the functional boards and from the system on the outside. Even though everything is functional, maybe it would be good to replace some of the electronics just in case, the system is 40 years old. Greetings.
web photo hosting
@Maximus
After you work out the problems with the electronics I would strongly suggest you turn your attention to the loudspeakers.
The speakers are using what look to be fine Braun/ADS drivers. These are very good quality (assuming the rubber surrounds are okay). I am sure that the crossovers are full of polycarbonate or mylar capacitors. If you want a big bang for the buck,replace these with polypropylene caps of the same value. No need for exotics here. You will be happily surprised at the improvement.
After you work out the problems with the electronics I would strongly suggest you turn your attention to the loudspeakers.
The speakers are using what look to be fine Braun/ADS drivers. These are very good quality (assuming the rubber surrounds are okay). I am sure that the crossovers are full of polycarbonate or mylar capacitors. If you want a big bang for the buck,replace these with polypropylene caps of the same value. No need for exotics here. You will be happily surprised at the improvement.
As I said before, Grundig developed and made their own drivers those days. And yes, you're right, the Compact Box 650 sounds amazingly fine, especially WRT it's size. I own a pair, too, but don't run them at the moment.
Check the 'lytics in the xover networks for capacitance deviation. If they have grown out of tolerance, replace them by film types if they're in the signal path or by new 'lytics if they're in parallel with the driver and there's a resistor in series with it.
Best regards!
Check the 'lytics in the xover networks for capacitance deviation. If they have grown out of tolerance, replace them by film types if they're in the signal path or by new 'lytics if they're in parallel with the driver and there's a resistor in series with it.
Best regards!
Unfortunately the system got defective again. A few days ago while i was listening to radio the right channel stopped playing and there is only a loud buzzing sound and the bass driver cone it goes all the way out and stays like that. Moving the balance all the way to the left channel doesn't make any difference. If i turn off the speakers from the speaker selector the buzzing stops. The left channel works without problems. What could it be the problem? Any advice will be much appreciated. Greetings.
Immediately disconnect the speaker from the right channel and measure output DC voltage - it is probably going to be way excessive. Sounds like you may have blown a transistor in the power amp or something.
I suggest you go through all the transistors in the right channel power amp with the diode test when powered off. Each transistor should look like two silicon p-n junctions back-to-back with no opens or dead shorts (both either facing the base or pointing away from it); look up their pinouts. Given that the fuse is not blowing, the output transistors may actually be OK, with a fault more towards the input side.
Only when that yields nothing suspicious, continue with resistors (especially in the feedback network and near the output, with special attention to fusible ones), diodes and other components. If unconclusive, you'll probably have to measure a bunch of voltages (starting from supplies) and compare them to the schematic and the other channel.
I suggest you go through all the transistors in the right channel power amp with the diode test when powered off. Each transistor should look like two silicon p-n junctions back-to-back with no opens or dead shorts (both either facing the base or pointing away from it); look up their pinouts. Given that the fuse is not blowing, the output transistors may actually be OK, with a fault more towards the input side.
Only when that yields nothing suspicious, continue with resistors (especially in the feedback network and near the output, with special attention to fusible ones), diodes and other components. If unconclusive, you'll probably have to measure a bunch of voltages (starting from supplies) and compare them to the schematic and the other channel.
Today I finally got a multimeter and measured the channel's DC voltage, I'm really new at this so I have no idea what to do. Here are two pictures, one from each channel, the first one is from the left, the second from the right channel. I got the setting on 200m on the multimeter while measuring. The left channel shows a constant numbers 09.8, the right channel usually is at 96.7 not more and variates and goes down to 0.01 and gets back.
I will open the system and try to measure the transistors for the right channel and will report back again. Hopefully I will do it right. Any advice is greatly appreciated.
Greetings.
I will open the system and try to measure the transistors for the right channel and will report back again. Hopefully I will do it right. Any advice is greatly appreciated.
Greetings.
Today I finally got a multimeter and measured the channel's DC voltage, I'm really new at this so I have no idea what to do. Here are two pictures, one from each channel, the first one is from the left, the second from the right channel. I got the setting on 200m on the multimeter while measuring. The left channel shows a constant numbers 09.8, the right channel usually is at 96.7 not more and variates and goes down to 0.01 and gets back.
I will open the system and try to measure the transistors for the right channel and will report back again. Hopefully I will do it right. Any advice is greatly appreciated.
Greetings.
EDIT:
The defect is in this board (the power amp board?). Switching on the other board that was firstly in the system shows no problem at the right channel. Any advice what should I do next?
Last edited:
Maybe it would be best to change all the capacitors including the big ones on the power amp board. Also I will change the trimpots and all transistors, or maybe just change with the transistors from the others board functional channel? The red ROE electrolytics did you know what value are they? It only writes 47/40 on them. Also where should I shop and what brands should I choose?
Greetings.
Greetings.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.