Hi guys! This weekend while getting ready for a rehearsal I switched on my PS-100, ensuring it was properly connected to my 1972 Marshall JMP 100 Super Lead and a speaker cabinet set to 4 ohms. I made sure the ohm settings were matched up, speaker cables were connected and working properly, etc. I am pretty sure the PS-100 was in Bypass mode while warming up, and after about 5 minutes I had taken the Marshall off of Standby mode, but volume knobs were all the way down, and nothing plugged into the inputs yet. I stepped out of the room to make a cup of coffee and heard a fairly loud pop coming from the speaker cabinet. I ran over to check and noticed a slight burning smell coming from the top of the PS-100 so I immediately powered everything off. Checked the Mains fuse and it was still good. I took it over to my work bench and unscrewed the top cover, and after a visual inspection saw that the internal fuse had blown. I could not see any other signs of other damaged or burnt components.
I ordered and installed a replacement fuse–0.63A 250V Fast Blow, powered it on again, connected it to the Marshall again. After letting it warm up for about 5 min I confirmed that I was getting sound in Bypass mode, but when switching to Operate and fiddling with the volume knobs I do not get volume out of my speaker cabinet. Or if anything, it is very very faint audio. However, my line out signal to my DAW sounds good, so the PS-100 appears to be working in Silent mode.
So I took it back to the bench, and I then tried removing the 12WD7 tube and installing an RCA 12AX7. Went back and connected everything and powered it up, again got full volume in Bypass mode, but nothing when switching to Operate mode. Line out signal is nice and strong.
Finally, got it back on the bench, put back the 12WD7 in, removed the stock 6550s and installed some new KT88s, went back and connected everything, powered it on and warmed it up, but again only getting sound out of the speaker cab in Bypass mode, but not in Operate.
Based on these preliminary steps taken to troubleshoot I think there may be an issue I’m not able to see. I checked all the ribbon connections and they appear to be sound and secure. Is there anything else you may suggest that I can do in the meantime? Or should I send it in for further evaluation? I purchased this brand new from Musicians Friend on 9/10/2021, so I believe it should still be covered under the 5 year warranty? Please let me know how to proceed. I really do love the PS-100 and hope it’s nothing major! Best regards, Dan
Hi Dan,
Thanks for the detailed rundown.
Two things I see in your rundown:
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After you replaced the fuse, your attention logically goes to other areas, but doesn’t mention the internal fuse again.
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The .63A internal fuse is not the correct value for the PS-100. That should be a 2A Fast acting type. It’s probably blown again, which aligns with your ongoing issue.
Here’s the link to the correct fuse: Search results for: 576-0217002.MXP Cartridge Fuses – Mouser
Either the HXP or MXP version is OK.
Check that our and let us know how it goes.
Hi David! So I also ordered 2A internal fuses a few days ago and replaced the 0.63A one last night and after some late night testing it looks like my PS-100 is working fine for now. Will keep an eye on it over the coming days, but thanks for the help so far!