Headline 1000 problem

This forum is for discussions on all kinds of Peavey bass amplifiers.
Post Reply
JB Lonewolf
New Member
Posts: 3
Joined: Tue Nov 15, 2022 4:13 pm

Headline 1000 problem

Post by JB Lonewolf » Tue Nov 15, 2022 4:16 pm

Hi. I've just repaired the preamp on a Headliner 1000 that was down, replaced two 4565's U4 and U5 which were leaking/ getting hot. Amp now works but here's the problem: when hitting the mute switch or turning it off without turning the master and gain down it bangs hard, and I mean hard. It killed my bench speaker. With the master off it's fine. I'm not really sure how the mute circuit works (or if that's the problem) but I've replaced mosfets Q8-13 and it hasn't made any difference. I realize these things are complicated but any suggestions would be greatly appreciated. Thank you in advance. JB

User avatar
j0nsnell
Member
Posts: 66
Joined: Wed Dec 21, 2022 1:33 am
Location: Jurasic Coast, Great Britain
Contact:

Re: Headline 1000 problem

Post by j0nsnell » Mon Dec 26, 2022 4:55 am

The High and Low side driver chip should mute (pin5 goes high) to stop drive to the power Mos Fets.
There is a PIC chip that is programmed to detect power down, amongst other functions and performs the mute/power off function.
It would help to know which chips you changed. I may have a better clue as to the issues with that knowledge.
I think the High/Low side driver is an IRS type but cannot cross reference the Peavey part number with the manufacturers part number so the type number would also help.

JB Lonewolf
New Member
Posts: 3
Joined: Tue Nov 15, 2022 4:13 pm

Re: Headline 1000 problem

Post by JB Lonewolf » Tue Dec 27, 2022 1:12 pm

Thank you for the reply. As it is I recently figured it out, and it was straight forward and simple. When the amp came in the power amp was fine, pre amp down. I found pre amp chips U4 and 5 were bad, replaced them and pre-amp came back, but now with a nasty bang when shutting down unless the master was turned off. Coming back to it after my aggravation wore off I started looking at the schematic (15 pages!)and checking voltages and bingo, there is a BAV99 duo diode invert connected to rail voltage and signal (near the chips that were bad), one side was shorted and bleeding +15 rail to signal. Funny how it didn't seem to affect anything else. I'm a humble repairman not an audio engineer and honestly don't understand the purpose of those backward diodes as many times as I've seen them in circuits, but the amp's out of my hair and I'm happy. Once again, thank you for the response.
JB

User avatar
j0nsnell
Member
Posts: 66
Joined: Wed Dec 21, 2022 1:33 am
Location: Jurasic Coast, Great Britain
Contact:

Re: Headline 1000 problem

Post by j0nsnell » Wed Dec 28, 2022 2:15 am

D7 & D8 are to protect the gate/inputs of the opamps from exceeding the rail voltages and thus minimising any damage from static pops and clicks.
Various double diodes are fitted withing the pre amp section as well.
Good to hear you have it working now. 👍

JB Lonewolf
New Member
Posts: 3
Joined: Tue Nov 15, 2022 4:13 pm

Re: Headline 1000 problem

Post by JB Lonewolf » Wed Dec 28, 2022 8:36 am

Thanks for the info. In this case it was one half of D4 that shorted, between shorted U5 and the mute circuit. I'll certainly pay attention to these diode circuits from here on.

Once again thank you,
JB

Post Reply