Onkyo M-508 Primary Fuse F801

jblmar · 21st August 2008, 03:21 PM

Hi all,
Working on an Onkyo M-508 for a fellow member. The primary fuse (F801) blows out on power up. The copy of the schematic is cut off just at the point of the circuit I need to check.
My guess is a short in the primary winding of the transformer. Another possibility is a defective component(s) futher down the line.
Anyone experience this problem in the past?
Thanks,

Ron

Jan Dupont · 21st August 2008, 03:32 PM

Maybe the circuit is here in the service manual

http://www.audio-circuit.dk/Schematics/Onkyo_M508.pdf

jblmar · 21st August 2008, 04:47 PM

Thanks for the schematic, ACD. Yep, F801 is direct to the primary of the transformer.
My guess is a short there.
Any one have this issue?

Ron

Jan Dupont · 21st August 2008, 05:49 PM

Have you tried disconnect the primary wires of transformer T001 and T002 measured the resistance? I could be a melt down in T001 windings.
If not, then try disconnect the transformer secondary wires at D801 Rectifier Bridge and see if problem is before/after the D801.
At the same time, you have the possibillity to measure the diodes in the D801 Rectifier bridge (one of them could be shorten)...

jblmar · 21st August 2008, 06:53 PM

Thanks for your reply.
I did check the bridge diodes. I didn't have time to disconnect the transformer(s) and measure their output or resistance.
The fuse goes up in a very bright flash.

Ron

Jan Dupont · 22nd August 2008, 04:18 AM

Disconnect and measure the restiance of the transformer windings WITHOUT connecting power.......

jblmar · 22nd August 2008, 01:16 PM

Yes, always measure resistance without power applied.
I'll check D801 & D802 tomorrow.

Ron

bekim · 22nd August 2008, 01:49 PM

Hi,

I have M-508 amp serviced 3-4 years ago and, as I can see might be one channel is blown if fuse pops up just like that.
But, yes you have to check the resistance of primary winding of the trafo's.

I think best is to check any transistor is showing short with your dmm. Or, any electrolyte (main ones) is leaking/short..

bekim

AndrewT · 22nd August 2008, 01:54 PM

Hi,
power it up through a light bulb tester and measure the transformer input and output voltages. That will reveal a lot.

jblmar · 24th August 2008, 12:42 AM

Removed both D801 & D802. F801 didn't blow out.
It's safe to assume that the secondary is o.k.
Could be either a B- or B+ short.

Ron

21st August 2008, 03:21 PM	#1
jblmar diyAudio Member Join Date: Dec 2005 Location: Brooklyn, New York	Onkyo M-508 Primary Fuse F801 Hi all, Working on an Onkyo M-508 for a fellow member. The primary fuse (F801) blows out on power up. The copy of the schematic is cut off just at the point of the circuit I need to check. My guess is a short in the primary winding of the transformer. Another possibility is a defective component(s) futher down the line. Anyone experience this problem in the past? Thanks, Ron

21st August 2008, 03:32 PM	#2
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	Maybe the circuit is here in the service manual http://www.audio-circuit.dk/Schematics/Onkyo_M508.pdf __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

21st August 2008, 05:49 PM	#4
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	Have you tried disconnect the primary wires of transformer T001 and T002 measured the resistance? I could be a melt down in T001 windings. If not, then try disconnect the transformer secondary wires at D801 Rectifier Bridge and see if problem is before/after the D801. At the same time, you have the possibillity to measure the diodes in the D801 Rectifier bridge (one of them could be shorten)... __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

22nd August 2008, 04:18 AM	#6
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	Disconnect and measure the restiance of the transformer windings WITHOUT connecting power....... __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

22nd August 2008, 01:49 PM	#8
bekim diyAudio Member Join Date: Jul 2004 Location: Prishtina, Kosova	M-508 Hi, I have M-508 amp serviced 3-4 years ago and, as I can see might be one channel is blown if fuse pops up just like that. But, yes you have to check the resistance of primary winding of the trafo's. I think best is to check any transistor is showing short with your dmm. Or, any electrolyte (main ones) is leaking/short.. bekim


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

21st August 2008, 04:47 PM	#3
jblmar diyAudio Member Join Date: Dec 2005 Location: Brooklyn, New York	Thanks for the schematic, ACD. Yep, F801 is direct to the primary of the transformer. My guess is a short there. Any one have this issue? Ron

21st August 2008, 06:53 PM	#5
jblmar diyAudio Member Join Date: Dec 2005 Location: Brooklyn, New York	Thanks for your reply. I did check the bridge diodes. I didn't have time to disconnect the transformer(s) and measure their output or resistance. The fuse goes up in a very bright flash. Ron

22nd August 2008, 01:16 PM	#7
jblmar diyAudio Member Join Date: Dec 2005 Location: Brooklyn, New York	Yes, always measure resistance without power applied. I'll check D801 & D802 tomorrow. Ron

22nd August 2008, 01:54 PM	#9
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, power it up through a light bulb tester and measure the transformer input and output voltages. That will reveal a lot.

24th August 2008, 12:42 AM	#10
jblmar diyAudio Member Join Date: Dec 2005 Location: Brooklyn, New York	Removed both D801 & D802. F801 didn't blow out. It's safe to assume that the secondary is o.k. Could be either a B- or B+ short. Ron

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Fuse housing melting but fuse not blowing, ppi amp	rawadia	Car Audio	21	2nd August 2008 10:39 AM
Why main fuse and not rail fuse?	digital desire	Solid State	10	3rd December 2006 08:07 PM
amp rating for fuse and fuse holder?	riotubes	Parts	5	27th August 2006 03:10 AM
Primary Impedance	alexmoose	Tubes / Valves	9	17th August 2006 04:34 PM
Need UTC PVM-3 primary ?	PTSOUNDLAB	Tubes / Valves	4	6th May 2005 04:54 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read