Adcom gfa 555 help

406vette

Member
2008-01-11 7:14 pm
I have an Adcom GFA 555 with a damaged input section. I have a 555 service manual but the front end circuit board (A020 A) and related parts list don't match. I understand two different boards were used for the 555 (not counting the 555II). If anyone has information one the other configuration (my board says S394V-0) I would greatly appreciate it.
 

bigcrabass

Member
2008-02-01 3:15 am
555 bias adjustment

I don't have an answer to your question, but I do have a 555 that I could take a look at for you. I am looking for the test points and bias voltages called out for the 555, but do not have the service manual. Does your manual cover this? I will go check the p/n of my board and report back
Bill
 

infinia

Member
2005-05-15 9:51 am
SoCal
Re: Anyone still got the manual

gooshpoo said:
Hi i have a GFA-555 from adcom that doesn't turn off, ive checked the switch and its bad. i replaced it and still same problem. so i need the service manual if anyone still has it my email is [email protected].
Thank you


This is a common failure, due to lack of mains surge limiting (ie slo start). I modded mine here on DIYaudio.
 

tsmith35

Member
2009-12-17 6:08 am
Okay, replying to my own post, but...

I emailed Adcom and asked about their apparently new charge for service manuals. Adcom stated that the charge was implemented in March 2009. So it looks like they won't be the source for any free service manuals going forward. They do provide owners manuals free through their website, though.
 

sindbaad

Member
2011-05-29 4:29 pm
I have a adcom gfa 555 ii which i recently got, the amp is mint in condition and runs perfect. However, the amp gets quite hot from the top right corner near the heat sink whereas, the right side of the amp runs cool (or gets warm not hot as the right side). Is this normal or means that there is something worng inside and i need to get it checked before something goes wrong?? please help
 
Well, there are several possibilities.
Just a couple of the more likely ones.

1. Check the bias of each channel . Are they comparable (within 20%). The service manual outlines the procedure and identifies the test points. You will need and volt meter and a power resistor.

2. Have you reconfigured you system recently? It is possible you now have something oscillating? You would not necessarilu hear it, but it would show up on a scope.

BTW, these are great amps and very good deal at their price point. However, they are getting older and probably desrve some TLC (replacing the electrolytic caps, some bypass caps, etc.)