Grundig Majestic 2028U-Restoration

I *might* have a parter set buried somewhere "very safe" (from being found) that I acquired for the trafo to fix another set, but repaired that one instead. If it magically appears, its yours for shipping costs.
 
Are you testing tubes? Usually most if not all of them are fine, it's the caps that went out and made it stop working, or it got put on the shelf because a new radio was purchased. I often find that a radio fires right up with just a recap.

I only had to replace the EM84 "Magic Eye" tube and the EL84 output tube.....everything else seemed to be fine.
 
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I *might* have a parter set buried somewhere "very safe" (from being found) that I acquired for the trafo to fix another set, but repaired that one instead. If it magically appears, its yours for shipping costs.

Great! Sounds good....just let me know.
 
Folks, here are a few more pics of the cabinet and radio. I haven't worked on the cabinet yet until I'm done with all the electrical work first. I'll keep ya posted of the progress as I go along with it.
 

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Quick update: I finally replaced all the coupling capacitors, power resistor, filter caps, and rectifier (silicon 1N4007) successfully. I also was able to find a perfect replacement power transformer that I salvaged from another Grundig tube radio (Model: 2520). However, after replacing all parts on the radio......I almost claimed a successful repair until I saw a faint smoke coming from the bottom of the radio. After taking a closer look underneath the radio, I came to find out a 2.7kohm resistor (R10) started overheating! I'm not sure what can be causing the resistor to overheat besides excessive amount of current going through it. Would anybody know or have any idea as to what is causing this issue? By the way, the 6x9 "woofer" gives out a big hum sound when the radio is powered on, but no sound. Only the tweeter gives out a bit of scratchy noise. Not to mention, none of the three bands seems to work when I tune to a certain station. Any ideas why?
 
Sounds like maybe problems in the power supply. The hum is likely from AC getting through.

Did you get all the electrolytic filter caps installed right way round? A backwards cap can do crazy stuff, right before it explodes.

Where is this 2.7k resistor in the circuit? Is it connected to a particular tube, filter cap, ?
 
According to the schematic, C7 and C13 if bad, could be a path to ground. If you pull the ECH-81 and it stops burning, it could be a bad tube also. You can use the chart of tube voltages at he top of the schematic to narrow it down. I don't understand the band switching terminals 9I, 9k, 9L to trace them out. I think from the switching diagram at the bottom, (K) gets connected to (I) or (L) depending on the band. I am unsure if all of the numbers (9) or letters (k) are connected together in the matrix.
I am using this schematic.
 

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Sounds like maybe problems in the power supply. The hum is likely from AC getting through.

Did you get all the electrolytic filter caps installed right way round? A backwards cap can do crazy stuff, right before it explodes.

Where is this 2.7k resistor in the circuit? Is it connected to a particular tube, filter cap, ?

The only electrolytic cap I replaced was the 50uF+50uF filter cap. I guess I overlooked any other electrolytic cap and only replaced the coupling ones. After carefully reviewing the schematic, it seems I missed the C35 and C52 caps. Would this be the cause of my issue? By the way, sorry for not posting the schematic but s-Petersen helped upload it. The 2.7k resistor taps into the ECH81 tube and the IF transformer I believe.
 
I've done a few Grundig 20xx series over the years. I have a beautiful blonde 2077 that plays in our bedroom most evenings. They are all pretty similar inside. They necessarily have a slightly high noise floor to begin with due to their design, which is quickly drowned out once you play a signal through it. But you should obviously not hear a heavy pervasive hum.

You are really well advised to replace every single paper capacitor on these before putting it back on the juice. No fancy caps, as it will become very boomy if you do. And also to thoroughly clean and test for function the pushbutton switch grid contacts. They DO get dirty, as do the tone wheels.

I presume you are doing a final voltage check out with all the tubes pulled? If you have access to a variac, bring it up to 85% of mains voltage, and you should be able to run down the test points. That is better than watching components burn up and smoke under load. Then if the raw values are ok, another voltage check out tubed, under load. If you are unsure if the tubes are good, then use known good ones. If you don't have a tester, find a friend who does. You will never get the set up with bad tubes.

When doing your initial audio check out, start with a test signal through the AUX ("PU") input first. If that proves satisfactory, then you move to the radio sections. Generally, these don't need realignment unless you have moved a core during the job.
 
I've done a few Grundig 20xx series over the years. I have a beautiful blonde 2077 that plays in our bedroom most evenings. They are all pretty similar inside. They necessarily have a slightly high noise floor to begin with due to their design, which is quickly drowned out once you play a signal through it. But you should obviously not hear a heavy pervasive hum.

You are really well advised to replace every single paper capacitor on these before putting it back on the juice. No fancy caps, as it will become very boomy if you do. And also to thoroughly clean and test for function the pushbutton switch grid contacts. They DO get dirty, as do the tone wheels.

I presume you are doing a final voltage check out with all the tubes pulled? If you have access to a variac, bring it up to 85% of mains voltage, and you should be able to run down the test points. That is better than watching components burn up and smoke under load. Then if the raw values are ok, another voltage check out tubed, under load. If you are unsure if the tubes are good, then use known good ones. If you don't have a tester, find a friend who does. You will never get the set up with bad tubes.

When doing your initial audio check out, start with a test signal through the AUX ("PU") input first. If that proves satisfactory, then you move to the radio sections. Generally, these don't need realignment unless you have moved a core during the job.

Thanks sgmlaw for the information. I did replace all the paper caps but I missed two electrolytic caps C35 and C52.....so I'll replace those as well. I did clean the switches, tone controls, and volume knob with Deoxit contact cleaner. I haven't done a voltage check out with tubes pulled out but don't have a variac to test it with. I would need to find someone that can lend me borrow one to perform these voltage checks. It's a good idea to test the audio through the AUX (PU) input first...didn't think of that. However, I did notice the 1.3k power resistor (which I replaced with a 1.5k 5W) on the output transformer gets pretty hot....is that normal?
 
Thanks sgmlaw for the information. I did replace all the paper caps but I missed two electrolytic caps C35 and C52.....so I'll replace those as well. I did clean the switches, tone controls, and volume knob with Deoxit contact cleaner. I haven't done a voltage check out with tubes pulled out but don't have a variac to test it with. I would need to find someone that can lend me borrow one to perform these voltage checks. It's a good idea to test the audio through the AUX (PU) input first...didn't think of that. However, I did notice the 1.3k power resistor (which I replaced with a 1.5k 5W) on the output transformer gets pretty hot....is that normal?
Yes, it is normal for that resistor to get warm. A 5w replacement is more than robust enough.

The OPTs on these are integrated into the power supply rails a little more tightly than in most designs.
 
I replaced the electrolytic caps and the 2.7k resistor that had burnt out, but I still can't listen to any radio station on either AM or FM. I can hardly hear a faint station on the BC band but nothing more. I did clean all tube sockets and tubes with some Deoxit cleaner, but no luck! Not to mention, the output speaker keeps making a loud hum even with the volume all the way down. I obviously replaced the filter cap but it still makes that humming noise. Would anybody know why I'm still getting hum noise? Perhaps, the output transformer might be shot? By the way, I notice smoke coming out from the 1.5k 10W power resistor(new) that's on the output transformer while the radio is powered on....any ideas why?
 
I replaced the electrolytic caps and the 2.7k resistor that had burnt out, but I still can't listen to any radio station on either AM or FM. I can hardly hear a faint station on the BC band but nothing more. I did clean all tube sockets and tubes with some Deoxit cleaner, but no luck! Not to mention, the output speaker keeps making a loud hum even with the volume all the way down. I obviously replaced the filter cap but it still makes that humming noise. Would anybody know why I'm still getting hum noise? Perhaps, the output transformer might be shot? By the way, I notice smoke coming out from the 1.5k 10W power resistor(new) that's on the output transformer while the radio is powered on....any ideas why?
Check that the full-wave rectifier doesn't have one or more shorted or open diodes. Check that the new filter caps are installed with correct polarity. Check the tubes for filament-to-cathode shorts.
 
Check that the full-wave rectifier doesn't have one or more shorted or open diodes. Check that the new filter caps are installed with correct polarity. Check the tubes for filament-to-cathode shorts.

The full-wave rectifier I'm using comes in an IC chip rated for 600V 1A...would it make any difference if I make one using 1N4007 diodes? As far as I'm concern, the new JJ 50uF+50uF rated at 500VDC is installed correctly per the schematic drawing, but I'll double check to make sure I do have the polarity correct. When the radio is on, all the filaments for all tubes light up and I'm getting around 6.3VAC, but I haven't checked filament to cathode shorts. I will give that a try and see my results. Thanks!
 
Also, I'm looking at the schematic and can't find a 1.5k 10w resistor connected to the output transformer. What is the part number on the schematic?
 
The full-wave rectifier I'm using comes in an IC chip rated for 600V 1A...would it make any difference if I make one using 1N4007 diodes?
Only if the rectifier unit is defective. It's easy to test it with an ohmmeter; verify that each diode has very high resistance in one direction and relatively low resistance in the other.
 
Also, I'm looking at the schematic and can't find a 1.5k 10w resistor connected to the output transformer. What is the part number on the schematic?
Also, I'm looking at the schematic and can't find a 1.5k 10w resistor connected to the output transformer. What is the part number on the schematic?
The schematic calls out for a 1.3k 3W power resistor but I replaced it with a standard 1.5k 10W resistor.
 
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