Awhile back I loaned out an Adcom GFP-555 to a friend and when it returned it had a rattle in it like something was banging around loose inside the pre. What I found was not what I expected, see photos below. The shell to the capacitor either came off or blew off. Sorry I don't have any photos of the shell but I did not see any signs of expansion. Any ideas what could of caused it?
Caps exposed to too high voltage blow the shells straight off. Goes with a bang. May have been a faulty cap?
It's a 50V, 22uF electrolytic capacitor that is part of a half-wave rectifier power supply.
Also check the associated parts, diode D902 and fuse F902.
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It's a pretty common failure mode for caps, actually. Usually the failure is more dramatic and you have shredded paper everywhere either that or the cap leaks and you find out about it when something else fails due to the corrosive nature of the electrolytic.
Make sure you clean up all the electrolyte with flux cleaner or the like. You need to get all of it as it is very corrosive.
Tom
Make sure you clean up all the electrolyte with flux cleaner or the like. You need to get all of it as it is very corrosive.
Tom
Thank you for the input. I checked the diode and fuse, the fuse was not blown and the diode looks good. Can these type of failures just occur?
Why I have the lid off should I replace the other caps? This pre is a backup to a backup and the one I typically loan out to friends in need. I have also toyed with the idea of finding it a new home but I never can bring myself to do it. Either way I don't want this to happen again which means I think I just answered my own question. 😀
Why I have the lid off should I replace the other caps? This pre is a backup to a backup and the one I typically loan out to friends in need. I have also toyed with the idea of finding it a new home but I never can bring myself to do it. Either way I don't want this to happen again which means I think I just answered my own question. 😀
If the other components look good then try replacing it.
If it blows again then there is another problem.
I have only seen caps do that from being in wrong way around or far to many volts on them. But I don't get involved with old gear much.
If the amp is of any age I would be replacing the electrolytics.
If it blows again then there is another problem.
I have only seen caps do that from being in wrong way around or far to many volts on them. But I don't get involved with old gear much.
If the amp is of any age I would be replacing the electrolytics.
Any brand of flux cleaner you would recommend? I don't know what I have currently have but I remeber the last time I used it, it left a sticky residue on the board.
Good point, haha.
Probably didn't use enough, like not enough water on your hands and they stay soapy.
I use plain old isopropyl alcohol to clean up such stuff.
I use plain old isopropyl alcohol to clean up such stuff.
Cleaned the board up and replaced the bad cap. Nothing went bang when I turned it back on so I guess all must be well. I am going to replace the rest of the caps while I am at it. I have read some even have gone so far as replacing the op amps in this. I am going to recap this pre for the experience before I dig into my GFP 710, and then GFP 750.
Question: Has anyone replaced the op amps in this and if so what with and what were your impressions?
Question: Has anyone replaced the op amps in this and if so what with and what were your impressions?
Only replace the electrolytics.
Only choose a voltage rating that equals, or exceeds that of the original.
Don't change any plastic film, nor any ceramic capacitors.
Don't change any semiconductors/ICs.
Only choose a voltage rating that equals, or exceeds that of the original.
Don't change any plastic film, nor any ceramic capacitors.
Don't change any semiconductors/ICs.
I appreciate every ones input. Below is a photo of my handy work. The lone black cap will be replaced soon, looking over the material list I must of forgotten to add that one to the order. There were two places where the traces came up off the board and I had to make jumpers. These were also the two worst caps when it came to black stuff around them. When I removed the caps I used isopropyl alcohol and cleaned the area up the best I could. Once I find suitable replacements for the OpAmps I will replace those as well. Probably a bit overkill for this pre but I'm enjoying the experience. Plus I would rather screw this up then say my GFP 710 or GFP 750 both of which are up next for a recap.
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Don't replace the opamps until you know how to check the circuit is behaving properly.
That takes resources and knowledge.
That takes resources and knowledge.
Other then testing all the functions on the preamp how would I test to see of the circuit is behaving properly? Trouble shooting is something I am trying/wanting to learn.
I was at Purdue all this week so I loaned this pre to a friend of mine to test. He said he got volume but after he turned the volume all the way up so it appears their is more problems that I need addressing. Other then checking for bad solder connections any other ideas? I will do a another visual inspection to see if any of the parts look fried as well.
This seemingly random post will make sense to bored184......
You need to check all the basics before condemning the relay (which is way down the list of suspects).
1/ Check that the PLUS 22 volt rail is OK from regulator Q902.
2/ Check that the MINUS 22 volt rail is OK from regulator Q901.
3/ Check that the PLUS 15 volt rail is OK from regulator Q906.
4/ Check that the MINUS 15 volt rail is OK from regulator Q905.
5/ Check the auxiliary negative volt rail that powers the front panel LED and also operates the muting circuit (relay 🙂) is present and correct. You should have around MINUS 30 volts on the anode (that's the non striped end) of D902.
Check all those 5 voltages first.
You need to check all the basics before condemning the relay (which is way down the list of suspects).
1/ Check that the PLUS 22 volt rail is OK from regulator Q902.
2/ Check that the MINUS 22 volt rail is OK from regulator Q901.
3/ Check that the PLUS 15 volt rail is OK from regulator Q906.
4/ Check that the MINUS 15 volt rail is OK from regulator Q905.
5/ Check the auxiliary negative volt rail that powers the front panel LED and also operates the muting circuit (relay 🙂) is present and correct. You should have around MINUS 30 volts on the anode (that's the non striped end) of D902.
Check all those 5 voltages first.
If I measured Q902, 901, 906 and 905 correctly I'm getting about +/- .5volts across them all. On D902 I get -1 V.
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That's not right.
Meter on DC volts, black lead to chassis (ground) and you should read -/+22 volts on Q901 and Q902 collectors. There is a 22 ohm ? feeding each collector. You should have the voltage on both ends of those. Check your meter is OK by measuring a battery.
Meter on DC volts, black lead to chassis (ground) and you should read -/+22 volts on Q901 and Q902 collectors. There is a 22 ohm ? feeding each collector. You should have the voltage on both ends of those. Check your meter is OK by measuring a battery.
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