Spider Valve HD100 input/codec board burnt

[AllanK]

Hi,
I have a Spider Valve HD100 which has cooked L2 on the Codec/Input board. It got hot enough to almost burn a hole straight through the PCB. According to the schematic L2 ties the analog gnd between the guitar input sub board and the analogue gnd on the codec brd. Has anyone experienced this before and if so, do you know the cause so that I can advise my customer?

[Jazz P Bass]

Would you be so kind as to point out 'where' L2 is on the schematic?

Spider Valve HD100 {Scheme}.zip

[Enzo]

Looks like the spark gap salesman came buy and made a successful pitch.

[AllanK]

Hi Jazz,
on page 1 of the schematic, on the RHS is a six way ribbon cable which connects the guitar in breakaway brd to page 2, the CODEC pcb. L2 is the third inductor from the top on a line marked as "600R @100MHz". It very efficiently vaporised itself along a portion of track and PCB. Enzo commented about the spark gap. There is one on the guitar input brd but it's right at the jack socket and any spike would have to take out a number of other components before getting to L2, even R45, a 1M resistor to AGND I would have thought would take the brunt of any surge first.

[Enzo]

I had never seen spark gaps on a guitar amp, then all of a sudden here are a pile of them. They did not figure into my thoughts on the problem though.

Now that I see where it is, my first impression still stands. I suspect something was plugged into the input jack with a voltage on its ground - with respect to this amp. You are correct as to what it connects. That choke was the weakest point, but it could easily have been a narrow point in a copper trace. This sort of thing happens when a "hot" chassis is plugged into that input. In other words something that was not itself well grounded. ANother common error is to inadvertently plug a power amp output into this jack. That might also damage the op amp - is that circuit working?

[MarkusBass]

I've seen such cases and they were caused, as Enzo says, by something plugged in with voltage on its ground. Ask the customer whether anything like this happened.

Mark

[AllanK]

Haven't checked the op-amp yet, I was feeling a bit gun shy as to what caused the burnout, so I'll power it up now and have a look. The customer has given me 4 new output valves so I have to set up the bias on them and let them run in as well. Thanks for your help, I'll talk to the customer and see what has been plugged in.

[AllanK]

Thanks Markus, will do

[Enzo]

He may not know, and you may never know. Someone helps set up the stage and makes the wrong connection. Oops, smoke. They then quietly remove the connection and don't tell anyone. Who else would know then? people often don't like to own up to their mistakes.

[drewl]

Possibly a ground loop from bad wiring.

I've seen the DI outputs fried from that.

[AllanK]

Hi fellow techs,
thanks for your assistance regarding the Spider Valve. I have had to repair the input board as I have been informed by Line 6 that replacement boards are no longer available. It took a while to get this information as I had to go through the Oz agents to find out. I powered up the amp and checked PSU voltages etc. and all good. The op-amp is fine luckily. The owner gave me 4 new Sovtek 6L6's to install and set up bias, which I have done and he is very happy. As it turns out when I returned the amp to him he said he had only had it 3 days, so the damage may had been caused pre purchase, so we may never know how....

By the way if any one is looking for the factory manual on this model (line 6 Spider valve HD100 Bogner), let me know and I can setup a drop box or something similar, it's too big for email (9.4Mb)

[Jazz P Bass]

Yes, please set up a 'drop box' for the schematic.