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Yamaha P-2250 headache

Willy6

Willy6

AK Subscriber
Subscriber
I’m wondering if the 2sk389’s are going bad?
I’ve checked resistors,replaced capacitors and transistors,checked diodes and I’m still getting around 630mv channel B and 700 mv channel A across the speaker terminals anyone have any ideas?
 
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It’s unlikely that the SK’s on both channels would go bad at the same time …

Edit 1: Is the amp in protection?
Edit 2: Check and readjust the idling current, then check the DC offset again.
Edit 3: Check IC401 pins 2 and 3, it’s common to both channels. What voltages do you measure?
 
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Sparkplug said:
It’s unlikely that the SK’s on both channels would go bad at the same time …

Edit 1: Is the amp in protection?
Edit 2: Check and readjust the idling current, then check the DC offset again.
Edit 3: Check IC401 pins 2 and 3, it’s common to both channels. What voltages do you measure?
Click to expand...
1:The amp is not in protection
2:The idle current is set at 12 mv
Dc offset is still high
3: IC401 pin 2 is 238.4mv pin 3 is 279.8mv
 
Willy6 said:
1:The amp is not in protection
2:The idle current is set at 12 mv
Dc offset is still high
3: IC401 pin 2 is 238.4mv pin 3 is 279.8mv
Click to expand...
So the amp is working, why are you measuring DC offset? Have you done any work on this amp? Was there anything wrong to begin with? A more complete description is really needed.

Also, worth checking the solder joints especially the ones on the RCA connectors.

Going to bed.
 
This amp has been sitting around for years and I decided that I needed another amplifier for tri amping a set of speakers so I pulled it out of storage and put it on the dbt and turned it on the bulb went dim and the relay clicked on so I checked and reset the idle current and then checked the DC offset and found that both channels were high. So then I started pulling and checking components on channel A and instead of putting the old capacitors and transistors back in I replaced them with new ones. So channel A has new electrolytic caps,transistors and a new VR after changing those components I reset the idle current and checked DC offset nothing changed DC offset is still around 700mv.
 
Please stop pulling components! No need to introduce new problems at this point.

If I were you I’d put the old xistors back in, new caps can stay in.

I hope you’re not taking these measurements on DBT. Once there are no shorts, you can go to mains directly and take measurements again. Please readjust the idling current off DBT first before measuring the DC offset.

Really going to bed now … :boring:
 
Willy6 said:
This amp has been sitting around for years and I decided that I needed another amplifier for tri amping a set of speakers so I pulled it out of storage and put it on the dbt and turned it on the bulb went dim and the relay clicked on so I checked and reset the idle current and then checked the DC offset and found that both channels were high. So then I started pulling and checking components on channel A and instead of putting the old capacitors and transistors back in I replaced them with new ones. So channel A has new electrolytic caps,transistors and a new VR after changing those components I reset the idle current and checked DC offset nothing changed DC offset is still around 700mv.
Click to expand...
If this uses a differential pair to set DC offset they have to be matched closely . Did you match them?

Athanasios
 
Sparkplug said:
So the amp is working, why are you measuring DC offset? Have you done any work on this amp? Was there anything wrong to begin with? A more complete description is really needed.

Also, worth checking the solder joints especially the ones on the RCA connectors.

Going to bed.
Click to expand...
There are no RCA connections on a P2250
 
The P-2250 has a DC servo to control the DC offset. IC201 a dual JFET input operational amplifier. (NJM072) Check the VCC pins on the opamp for correct voltages. Pin 4 and pin 8 for +/- 15 vdc.
 
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avionic said:
Bingo. Check the output of IC103 voltage regulator for +15vdc. Check fuse F103 on the input board with your multimeter. IC103 is on the same board.

Output of IC103 is pin 3. Not pin 2 as illustrated in the schematic.

just in case.

Click to expand...
Bingo both IC 103 and 104 are loose in the board and might just need resoldering.
That board looks like a pain to get out though.
 
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