Please help, I've wrecked my Beresford

[James G]

Hello everyone, my first post and all. Great forum, so many interesting things here.

I'm new to the audio mod stuff and I tried to mod21 (http://www.beresford.me/Downloads/Mod21.pdf) my Beresford and it didn't like it, so now I've got two of them. I'm terrified to try anything with the 2nd one at least until maybe I can figure out what went wrong with my first attempt.

What happened is right after I performed the solder bridge part I hooked it back up and tried it out. It started playing initially, then after about 20 seconds the left channel started crackling, then quit. I'm pretty sure I didn't burn anything up with the iron and I checked the connections with a ohm meter and they seem to be sound. But I don't really know where to start troubleshooting this.

If you guys have any ideas for me to try your suggestions would be greatly appreciated.

[NRG]

Can you take an in-focus close up shot of the inside and post it?

Did you get the 'lytic caps the correct way round?

[leo]

Hello everyone, my first post and all. Great forum, so many interesting things here.

I'm new to the audio mod stuff and I tried to mod21 (http://www.beresford.me/Downloads/Mod21.pdf) my Beresford and it didn't like it, so now I've got two of them. I'm terrified to try anything with the 2nd one at least until maybe I can figure out what went wrong with my first attempt.

What happened is right after I performed the solder bridge part I hooked it back up and tried it out. It started playing initially, then after about 20 seconds the left channel started crackling, then quit. I'm pretty sure I didn't burn anything up with the iron and I checked the connections with a ohm meter and they seem to be sound. But I don't really know where to start troubleshooting this.

If you guys have any ideas for me to try your suggestions would be greatly appreciated.

Post a couple of close up pics and we'll first see if we can see anything obvious .

I don't have one of these dacs but should be able to spot anything that looks suspicious

What I'd do is check the signal lines on a scope from the dacs output pins and further up stream

If you changed the capacitors as in the mod21 pdf be sure they are in the correct way around

The op-amp may have blown on one side, this can be caused by shorts or over heating of the pins

The dac chip may have blown its left side (unlikely)

There maybe a tiny intermittent solder short

If you give up and feel like binning it , sell it me

[Covenant]

Boy oh boy am I glad I got Stan to do mine.....
I learnt my lesson trying to mod a Trends amp with the Audiomagus kit-I had to send it off to get almost completly rebuilt.
Good luck

[James G]

Can you take an in-focus close up shot of the inside and post it?

Did you get the 'lytic caps the correct way round?

Everyone thanks for the replys. Attached is a photo. I don't think I broke anything, but who knows. The small wire is a silver plated copper strand I used to bridge the gap. If I leave it on for a while I can start to hear it sputter through the left channel once in a while like it's trying to come back to life. The right channel sounds fine though.

The problem happened before I changed the caps, but now I have changed them to 47uF/16v and double checked to make sure they are positioned the same as in Stan's pdf.

[leo]

When the sound goes down do you still get DC voltage to the coupling capacitor on the faulty side? does it measure the same as the side which is ok

Maybe you could remove the output coupling capacitors and run a wire from the coupling capacitors before the op-amp to the neg marked hole of the output capacitors if that makes sense? you then would be bypassing the active op-amp output stage

If it works this tells us the dac chip is ok and the fault is around the op-amp

[leo]

Also carefully check the solder joints on the phono sockets etc, its possible there was a weak solder joint and after doing the mods it could have upset it

I presume theres no sound on the same channel headphone outputs or variable out?

[StanleyB]

The problem happened before I changed the caps, but now I have changed them to 47uF/16v and double checked to make sure they are positioned the same as in Stan's pdf.

Doing half the mod first is the likely cause. The 4558 might have done a Luke. The mod21 involves changing the output stage configuration and biasing method. You are going to need a scope to check if the audio signal on the output of the PCM1716 is OK, and if it is also OK in and out of the 4558. I reckon Leo would figure that out in less than 5 minutes.
My advise: don't tamper with your other TC-7510, cut a deal with Leo, and take up the AoS member's offer on the TC-7520. And leave the latter well alone mod wise...

Stan

[James G]

Leo, Stan Thanks for stopping by. I've been reading a lot from you guys and got really interested in this stuff.

I don't have an oscilloscope or anything like that, just a mulitimeter. I guess I can try measuring the DC voltages from side to side. Maybe I'll see something that's obvious even to me.

It's worth $5 for me to stop by Akihabara and pick up a couple of chips to try out. If it's the opamp I might be ok, but if it's the dac chip I think I'm doomed. I don't have the finesse to change that out. So for that reason I'm hoping it's just the opamp that's the issue here.

[James G]

Oddly enough, when I got home from work I turned it on just to see and both channels were playing! But it was pretty distorted and after about 1 minute I could hear it starting to fade out so I just turned it off. Guess it's time for more probing...