Probably should elaborate... that one second is the usual protection circuit delay, then the LED on the front goes from orange to green, but just for an instant. The bulb lights, and I believe its power consumption sends the system back into that protection delay. So I guess better the light bulb flash than a bunch of fuses blow or worse. I only wonder if it's possible that the bulb is preventing the amp from properly starting up because of that protection circuit.
If you want to take the DBT out of the equation - up your bulb to 100w, still provides protection but will allow more than enough current for the NAD to start up.
Question - did you alter the bias pot at any time during your repair or troubleshooting? Small chance that if you did, the replacement parts have the bias set too high and is current limiting.
Second question - have you checked for DC on the outputs (prior to the relay) to see if it is going into protection mode. Would only take 1-2V on the speakers to kick-in protection.
Last thought - if you can, disconnect both amp boards and see if just the power supply will start up, or does it still cycle? if PSU is good, then connect one board at a time and confirm the culprit is the one you have done the work on.
I know this last one might be very difficult, because I think the connection to the board(s) also includes the protection, so disconnecting it does not allow start-up of the power rails.
I know that earlier 214/216 NADs are notorious for bad relays, because they are right next to very hot running components, voltage dropping resistors and regulators. Not familiar with this design, but that could be another long-shot item.
Question - did you alter the bias pot at any time during your repair or troubleshooting? Small chance that if you did, the replacement parts have the bias set too high and is current limiting.
Second question - have you checked for DC on the outputs (prior to the relay) to see if it is going into protection mode. Would only take 1-2V on the speakers to kick-in protection.
Last thought - if you can, disconnect both amp boards and see if just the power supply will start up, or does it still cycle? if PSU is good, then connect one board at a time and confirm the culprit is the one you have done the work on.
I know this last one might be very difficult, because I think the connection to the board(s) also includes the protection, so disconnecting it does not allow start-up of the power rails.
I know that earlier 214/216 NADs are notorious for bad relays, because they are right next to very hot running components, voltage dropping resistors and regulators. Not familiar with this design, but that could be another long-shot item.
While using the bulb tester try turning the bias presets VR103 and 104 to minimum resistance and see if that helps.
The 63v 100nF's are fine on 50v rails.
The 63v 100nF's are fine on 50v rails.
Fixed!
I did have those VRs at minimum, but the 60W bulb was limiting the current too much to get out of protection. I think if I'd let it run longer those caps might have charged. Not sure, because I got my hands on a 100W bulb this morning. It still did the cycling in and out of protection, but the bulb was dimmer each time, and after 6 or 7 cycles it fired up. Once I was confident it worked, I took it off the limiter and tweaked the bias and idling current VRs for a while, and I'm pretty sure that's that. It works and sounds great. Back into service it goes. Hopefully these new caps (everything I bought is rated for at least 5000 hours at 105°C) do better than the originals.
Thanks to everyone for your help on this. Maybe this thread will be useful to someone else with this amp. All told it cost me about $150 to fix the C350.
I think I'll start another thread for doing a bit of work on this:
It works and sounds good, but has never been worked on, and is about 50 years old (the original owner told me he bought it in Taiwan on his way home from his tour in Vietnam). There's a lot of hum on the headphone output, which I'd like to see if there's something to be done about.
I did have those VRs at minimum, but the 60W bulb was limiting the current too much to get out of protection. I think if I'd let it run longer those caps might have charged. Not sure, because I got my hands on a 100W bulb this morning. It still did the cycling in and out of protection, but the bulb was dimmer each time, and after 6 or 7 cycles it fired up. Once I was confident it worked, I took it off the limiter and tweaked the bias and idling current VRs for a while, and I'm pretty sure that's that. It works and sounds great. Back into service it goes. Hopefully these new caps (everything I bought is rated for at least 5000 hours at 105°C) do better than the originals.
Thanks to everyone for your help on this. Maybe this thread will be useful to someone else with this amp. All told it cost me about $150 to fix the C350.
I think I'll start another thread for doing a bit of work on this:
It works and sounds good, but has never been worked on, and is about 50 years old (the original owner told me he bought it in Taiwan on his way home from his tour in Vietnam). There's a lot of hum on the headphone output, which I'd like to see if there's something to be done about.
Excellent result 👍
The caps should last forever.... 5000Hrs @ 105C probably gives 10,000 hours at 80C and more like 50,000 at 50C. That sort of progression 🙂
The caps should last forever.... 5000Hrs @ 105C probably gives 10,000 hours at 80C and more like 50,000 at 50C. That sort of progression 🙂
Yep, a new thread 🙂
Service manual is here:
https://www.hifiengine.com/manual_library/pioneer/sx-1000tw.shtml
It looks really old the way its all written but it should be fixable.