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Old 13th March 2014, 12:13 PM   #1
john65b is offline john65b  United States
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Default Parasound 2250 Amp Schematics?

Anyone have schematics to a Parasound 2250? I have one that goes into PROTECT....already replaced bad recifier on PS board, and a shorted Diode on R channel amp board.

No shorted output devices.
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Old 13th March 2014, 04:08 PM   #2
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Send an email to Parasound, they're great. I've even received info on Sundays!

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Old 14th March 2014, 04:20 AM   #3
john65b is offline john65b  United States
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Thanks - Sent a request for schematic - I received a reply from Richard Schram asking to call in to the tech department tomorrow morning...I am not expecting much in the way of a schematic...

Does the amp go into "PROTECT" if the output relays are shot? Or does the "PROTECT" just shut down the output relays?

I checked voltage on the Bias Servo Opamp and have 16.5v so I think input servos are good... so I connected the speaker directly to left channel output off amp board (upstream of output relays) put in a signal and got music, so the left channel amp appears to work ok, so "PROTECT" does not affect the input to amp...

Right channel amp board has issues - found all three 2SK3519 output trannies shorted, as well as one IRF540. I already changed the 3A diode as it was shorted too...

Anyway, I hope this is worth the work. I initially thought the only issue was the fried rectifier on the power supply... .
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Old 14th March 2014, 01:21 PM   #4
john65b is offline john65b  United States
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Quote:
I checked voltage on the Bias Servo Opamp and have 16.5v
Um, I meant the DC Offset Servo Circuit...
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Old 14th March 2014, 02:41 PM   #5
john65b is offline john65b  United States
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Wow, called Tony, talked a bit, and he is sending me the Schematic. How cool is that?
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Old 30th April 2014, 12:58 AM   #6
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Well got the amp working. Replace the three output transistors (C3519) that were continuously blowing, and the two transistor in front (D669A and C1815). All is good now ..except the PROTECT circuit is still on. High and Low Rails are good, and Input Servo Opamp circuit is OK as I get no DC offset

If I take the output right from the amp modules while in PROTECT, all good - perfect (yes I checked for DC first). I eventually just pulled the mute connector and now get music out of the amp binding posts while PROTECT lights. Like I said, the amp is now working perfectly and biased (1.5v across the .1 emitters - per Tony) and amp sounds very good. The Turn on / turn off relays even seem to work properly with PROTECT...strange...

Anyway Tony at Parasound was nice enough to point out the three transistors in the PROTECT circuit (BF421 and BF423) on the AMP board. They have been replaced and there are no shorts or any issues with these transistors.....nor are there any issues with the caps/resistors/diodes in that circuit that I found...but still get PROTECT

Anyway I really don't wanna post the schematic for help unless it is OK... I am 95% there!!!
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Last edited by john65b; 30th April 2014 at 01:02 AM.
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Old 2nd May 2014, 02:44 AM   #7
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What else beside DC is the protection circuit sensing? Like I said DC is non existent - 1.4mv and 2mv at the binding posts...so should not be in PROTECT, at least not because of DC on output......
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Old 2nd May 2014, 10:50 AM   #8
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Protect circuit itself may have a fault.

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Old 2nd May 2014, 11:47 AM   #9
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If one supply is missing, that will cause the protect circuit to engage.
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Old 2nd May 2014, 12:04 PM   #10
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You mean having just one properly functioning amp board connected in the unit will trigger PROTECT? That is good to know. I have wondered this.

Still the issue remains. Like I said, sounds great, no issues anywhere. Just the PROTECT. I have the mute connector pulled, so the amp performs as it should...

The Protection circuit is on the Amp board (according to Tony). The "protect" pinout on connector from power supply to the amp board has + rail voltage (50vdc?). Since I pulled the mute connector on the input/output board and speaker out relays work as intended, so the mute is looking for no signal to work properly.

The three transistors appear fine (no shorts/open) and everything else (cap/resistors,diode, etc) also appear fine...
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