EP1500 Pure DC on Channel 1

ATech · 3rd April 2009, 01:55 AM

I'm currently having a little trouble on an EP1500 amplifier I have been working on after it experienced catastrophic failure. I have just replaced the MJE15032 & MJE15033 NPN & PNP Power Transistors along with 2SC5200 & 2SA1943 TOSHIBA Transistors which had been taking out the main module slow blow fuse on channel 1. I have also replaced the 4 Zener Diodes. Channel 2 works great but channel 1 just produces DC. Everything checks out ok but I think I may have missed out something out. I have been using the schematic and tracing all related components and all voltages check out well but this is only with a voltmeter. At the moment I don't have access to a scope. Any suggestions

ceharden · 5th April 2009, 01:36 PM

I would be interested to see the schematics if possible and it would really help me make any suggestions.

Have you checked the feedback loop and assuming it uses one the LTP differential amplifier.

wg_ski · 5th April 2009, 02:53 PM

Make sure you didn't toast the emitter resistors of the 15032 or 15033. Or anything else besides the zeners in the bias stack-up including the 'signal present' indicator and its driver circuit.

kevvywevvywoo · 5th April 2009, 10:14 PM

Such is the level of DC coupling on this type of amp that literally any component failure from back end to output can give a DC condition...its a chicken-and egg condition. I recommend extensive cold checks esp. the op-amps which can and do fail here.

3rd April 2009, 01:55 AM	#1
ATech diyAudio Member Join Date: Jun 2008	EP1500 Pure DC on Channel 1 I'm currently having a little trouble on an EP1500 amplifier I have been working on after it experienced catastrophic failure. I have just replaced the MJE15032 & MJE15033 NPN & PNP Power Transistors along with 2SC5200 & 2SA1943 TOSHIBA Transistors which had been taking out the main module slow blow fuse on channel 1. I have also replaced the 4 Zener Diodes. Channel 2 works great but channel 1 just produces DC. Everything checks out ok but I think I may have missed out something out. I have been using the schematic and tracing all related components and all voltages check out well but this is only with a voltmeter. At the moment I don't have access to a scope. Any suggestions __________________ Kind regards AT

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5th April 2009, 01:36 PM	#2
ceharden diyAudio Member Join Date: Nov 2005 Location: Southampton	I would be interested to see the schematics if possible and it would really help me make any suggestions. Have you checked the feedback loop and assuming it uses one the LTP differential amplifier.

5th April 2009, 02:53 PM	#3
wg_ski diyAudio Member Join Date: Oct 2007	Make sure you didn't toast the emitter resistors of the 15032 or 15033. Or anything else besides the zeners in the bias stack-up including the 'signal present' indicator and its driver circuit.

5th April 2009, 10:14 PM	#4
kevvywevvywoo diyAudio Member Join Date: Aug 2008	Such is the level of DC coupling on this type of amp that literally any component failure from back end to output can give a DC condition...its a chicken-and egg condition. I recommend extensive cold checks esp. the op-amps which can and do fail here.

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