Hello I’m new to this forum and new to electronics. Hoping for some direction. I bought this 2245 about 10 years ago in working condition and had planned to someday do a full recap on it. It’s been in storage in my house for the last two years now when I turn it on, it’s got a lot of problems. I have it plugged into a dim bulb tester. First power up was sound on FM but switching the selector to a.m. to FM the DBT lit up and a loud pop went through the speakers. I turned it off. Try it again on FM. It worked fine. FM’s working, sound is coming through. I turned the bass tone knob up and again the DBT lights up makes a pop. I turn it off. Turn it back on. It’s fine. I push the main speaker selector on and off and it also lights up the bulb with a pop sound at the speakers. It seems like everything I touch causes a short? I’m not sure where to start looking for the problem? Here is what I’ve done. I used deoxit on all of the pots and switches, tightened up the nuts on the front of pots, cleaned the interior with compressed air. I don’t see any obvious burnt capacitors, diodes or anything else. I noticed it has mismatched output transistors. One side is Texas Instruments and the other side is NTE. But basically it plays sound out both speakers just fine if I don’t touch any of the switches and just power it on, as soon as I make any adjustments, the bulb lights up at approximately 50% brightness , and it makes an electrical sound and pop through the speakers. I have a power supply rebuild kit sitting here, but haven’t attempted anything yet. Any help or suggestions would be greatly appreciated!
Marantz 2245 Basketcase?
- Thread starter thejet95
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- marantz + 2245
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It's not the best idea to adjust the +35V, or anything else, if on the DBT. I recommend returning the adjustment to +34.4Vdc. What wattage is the DBT bulb? Is it incandescent? The NTE transistors are not very good, once it's all working replace them with OnSemi MJ21193 and 4. Then spray some Fader F5 in the pots, the DeOxit there is not recommended. If it were me I'd pull the preamp to main in jumpers on the back and rebuild the power supply. When you measure the two output voltages also switch your meter to AC and verify that there is only a few mV of a reading.
Thanks for the recommendations! I have a 160 watt incandescent bulb in there. I had read the higher wattage the better. I’ll try the fader f5. What does pulling the jumpers in back do?
Bill S
Thread Killer
Clean all the controls and switches (source switch as well) thoroughly. Use a 75w bulb in the DBT. Use the DBT to ensure no shorts and if so, power up off the DBT and set voltages.
Okay makes sense I will try this! Awaiting some fader f5 to arrive and I’ll get to cleaning!
Not necessarily on the wattage. Too high can allow too much current and not be as protective as it can be. I'd use a 60 watt or even less for a 2245. The jumpers pulled will isolate the preamp from the amp. If it still makes pops when things are changed that points more towards a mechanical fault like a dirty switch, or a cold/cracked solder joint or the like in the amp. Else it's on the preamp side.
icko30
Super Member
From chat gpt :
Using the amplifier’s power rating to select a bulb wattage works effectively in a broad sense, even if it doesn’t directly represent the amp’s actual current draw at idle or low power. It's a practical rule of thumb that makes the dim bulb test convenient and accessible for most hobbyists.
ps
Smart guy.
Using the amplifier’s power rating to select a bulb wattage works effectively in a broad sense, even if it doesn’t directly represent the amp’s actual current draw at idle or low power. It's a practical rule of thumb that makes the dim bulb test convenient and accessible for most hobbyists.
ps
Smart guy.
That makes perfect sense thank you! I’m excited to get this fixed!
Okay so here is the update. I replaced all of the capacitors in the power supply, cleaned the pots and switches with deox fader f5. Put new LED bulbs in too. So it powered up just fine without speakers plugged in yet. It lit up my 75 watt DBT dimly for a split second and the went off. Turned off and on several more times and no more lit bulb. Then I plugged in both speakers and powered on. Tuned to an FM station on low volume and it sounded good. Pushed buttons and switches no pops or anything. Then not touching anything and listening to the radio for a few minutes it suddenly made an “electrical buzz sound” out the speakers and the DBT lit up, the lights on the front went off. I turned it off and on, same, no lights in front and electrical sound from speakers and DBT lit up. I unplugged both speakers and it turned back on face all lit back up and DBT off. Would this mean my problem is in the amplifiers or output transistors? What would be the best next step? Thanks!
So you didn't check the bias, offset, or power supply output? Not the best call....
The output transistors are part of the amplifiers, what do you mean?
Check the output and driver transistors for shorts. Check power supply voltages. Something bad happened. Also don't run speakers on a DBT, use headphones.
I apologize I forgot to mention I did check the bias and offset. Someone else earlier suggested I test with plugged into the wall not on DBT. After replacing power supply capacitors I got 34.99 volts with leads on j802 and j803 and was able to adjust to exactly 35 volts and it was stable. Both left and right channels DC offset was 0.002, and I switched to AC voltage and got approx 1.19 volts on both channels. I didn’t test power supply output, I just read about that. I also tested with the headphones and it sounded fine that’s why I proceeded to connecting the speakers because I was excited that the power supply fixed the issues. I tried the headphones again and it sounds fine for a few minutes and then the right side starts to become increasingly static. I also disconnected the rca preamp to mains and the headphones still have static on the right side. I’m new to all this that’s why I’m asking for help. It’s much appreciated!
Ok gotcha, yes you did all the right things and I would have thought the unit was good to go as well.
If the issue still happens when you remove the jumpers, it’s the amplifier section. Replace the 3 small signal transistors on the board, the 2S 945 and the input pair. Don’t worry about the current limiting pairs.
While you’re there, I would recap and replace the zeners and trimmers. The bias transistor too.
Okay thank you!
Okay I didn’t know about that sticky ill check it out!