Just got an Adcom 5400, Chinese manufactured 1998, and I opened it up to make sure none of the fuses was blown, and looked at the power supply caps. I see some dark brown at the edges of the caps and it's been noted in other posts that that was a mastic to hold the caps to the board but all of them are loose to light pressure. Should I assume it's the mastic? The tops of the caps are slightly convex. Should I therefore assume they're bad and leaking? No caps I've seen with suspected leakage ever turned out to be bad when I removed them. If it works ok without hum, should I assume it's just mastic goo?
I couldn't really get the extent of the convexity of the tops of the caps but they are all equal and push in just a bit
May be ok, but a Variac is always nice to use for this.
If the amp has individual rail fuses for each channel, power just one channel at a time.
Check for output DC voltage offset.
If the amp has individual rail fuses for each channel, power just one channel at a time.
Check for output DC voltage offset.
Already checked DC offsets, very good like 1 and 3mv. I havent hooked up a source yet; will use a disposable speaker to start. Eventually will be my fronts for stereo and home theater
The brown gunk is often residue from some form of glue used to hold the caps in place. The plastic lids on top of these capacitors do sometimes bow ( there is a discussion somewhere on this forum where Nelson Pass references this - has to do with the wrapping applying pressure on the isolation disc and not the capacitor itself ) . I have a 5200 and a 5300 and have not changed caps in either - both measured perfectly and have been functioning as a lab amp / office amp for years now. The stock amps run fairly low bias - it is possible to improve their sound simply by increasing their bias points to a point where the heatsink temp is acceptable ( my leave on all the time and don't stress temp is 45-50 degC )
it is more tonal character imo
here is the original thread that sparked my original interest
https://www.diyaudio.com/community/threads/summer-consolation-amplifier-1995-adcom-gfa-5200.197406/
here is the original thread that sparked my original interest
https://www.diyaudio.com/community/threads/summer-consolation-amplifier-1995-adcom-gfa-5200.197406/
Nelson Pass often makes comments here. Also he designs some of the projects in the diyAudio store,
and contributes some of the parts for the projects.
and contributes some of the parts for the projects.