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prob w/ adcom preamp

cdfac

cdfac

AK Subscriber
Subscriber
Not the most vintagey item, but my Adcom GTP-500 preamp has been acting up today. It will suddenly shut off, or switch to a different input source, or both. The first time I thought it was a fluke, and after turning it back on it was fine. But tonight it hasn't been able to stay on. It hasn't been pushed, it isn't hot. I'm going to try unplugging it for a while and then see what happens. Any ideas as to the cause or a fix? Thanks.
 
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With the type of button, I'm sure it uses a chip to switch inputs. Someone else suggested a chip might be overheating, likely triggering the protection circuit. I tried a different surge protector outlet and let it play for an hour after letting it sit for a while, and I didn't have any problems. I will give it another couple of hours of play when I can and see if it happens again.

If it is an overheated chip, wouldn't I be able to open it up and tell by feel who the culprit is, assuming I could reach it and avoid the caps? I remember that they could get awfully hot in my college electronics course. Thanks.
 
I have the same pre and have had similar problems with the inputs (although mine has never turned itself off).

I always selecet the right input and it seems to work fine for a while. Yours must be a little sicker than mine.

-Matt
 
It went a long time with no problems except one shutdown, then last night it started to go crazy. I was listening to some CDs and noticed some flashing out of the corner of my eye. After convincing myself I wasn't imagining things, it turned out it was the radio preset buttons. The radio starts changing stations slowly, becoming increasingly erratic, and the lights flash more as well. Nothing affecting the sound while listening to CDs though. Is this definitely a case of an overheating chip?
 
sounds like the main micro is going nuts... perhaps check your power supply voltages, more so check the +/- 5 v rails and the +/- 12 rails ( i would assume it has all four) if you measure anyhing more than a 3 % variance using an accurate meter like a fluke mind you... then chances are your ault will be there.check it on a cro as well... if u see noise, then the power supply caps are prob stuffed. i would reccomend replacing and perhaps upgrading all the capacitors in the power supply anyway. check them out, they may well be rated at 85 deg celcius.. if so, get rid of them and replace with caps rated at 105 degrees. good luck!!!!!!

mind you microprocessors dont need much ripple in the supply to play up mind you. sometimes it can be immeasurable with even reasonable equipment.
 
could anyone shoot me a schematic or labeled nude pic so i can figure out what's what? would be much appreciated.
 
after another period of quiet, it has again gone schizo, perhaps now in a way that will lend to a more exact diagnosis...

the fm station changing very quickly deteriorated into an power-on/off loop that is continuing as we speak. with no help from me, the unit turns itself on and off every 5 or 10 seconds, switching inputs and stations in the process. there is also a noticeable level of static even with the volume turned down which is consistent across all inputs. it's been on all day without problems. unplugging for 10 minutes did not fix it like before.

bad voltage supply or just faulty chip? i'm really mad now because i just got my new infinity WTLCs fixed and i can't even enjoy them...
 
1- Leave it unplugged over night. If it needs 'reset' it may require longer time than a few minutes.

I wonder if it has the tiny contacts like Pioneer Elite gear?? I know they are old enough now to start acting out. . .
 
Guess I'll add my 2 cents.

I had a problem with my TA-E80ES preamp similar in the sense that the protection circuit tripped (when there was some sort of AC surge) I could not change inputs or anything like that, even though the preamp powered up, thought I blew the main CPU. After a couple hours of tinkering to no avail, I unplugged the unit and left it overnight, came back the next day and it worked like a charm, so maybe something needs to be reset?

Othewise look inside at any connectors that may be lose or need reseating? Maybe a cold solder joint somewhere? :scratch2:
 
something else weird happened this morning. sometimes i like to use my laptop as a jukebox, and i use a standard miniplug-to-stereo cable to connect to the preamp. but the second the miniplug touched the jack on my soundcard, the adcom went crazy like usual. i think this is the second time this type of thing has happened, too. the cable is hooked up to the Tape 1 input. i think i've got a gremlin inside there!
 
Try tightening the screws that mount the PC card to the chassis. Also tighten all ground screws and lugs
 
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