98jetta
New Member
Hi folks,
Picked up a GTP-400 well aware of the issues they have with the FM section - usually fixed by replacing a variable cap relating to the FM circuit. After reading many threads on this preamp I don't think that's what is biting me.
Both AM and FM, while stations are locked and signal strength looks good (stations I know should tune well), come in at incredibly low volume which is at an equivalent level across AM and FM. Volume knob at full is barely audible - but it is a clear sound nevertheless for both AM,FM. Other inputs work just fine, and everything else seems perfectly ordinary.
I've spent some time giving all of the switches, knobs a good cleaning as a first step and there was no improvement. I inspected the board and all of the joints look fine, and I tried moving various components during operation to identify solder issues I couldn't see. Tested voltages vs the schematic for the FM, AM related ICs and those look good so my assumption is that those sections are receiving the correct power but I'm not an expert. On a whim I re-flowed the solder on all of the input selector legs and that didn't help either.
Any ideas on what to test next before I randomly start testing components? I can't really tell what is common between AM & FM circuits to test those things explicitly but that is my instinct on where the issue lies.
https://www.hifiengine.com/manual_library/adcom/gtp-400.shtml if you want to take a look at the schematic!
Picked up a GTP-400 well aware of the issues they have with the FM section - usually fixed by replacing a variable cap relating to the FM circuit. After reading many threads on this preamp I don't think that's what is biting me.
Both AM and FM, while stations are locked and signal strength looks good (stations I know should tune well), come in at incredibly low volume which is at an equivalent level across AM and FM. Volume knob at full is barely audible - but it is a clear sound nevertheless for both AM,FM. Other inputs work just fine, and everything else seems perfectly ordinary.
I've spent some time giving all of the switches, knobs a good cleaning as a first step and there was no improvement. I inspected the board and all of the joints look fine, and I tried moving various components during operation to identify solder issues I couldn't see. Tested voltages vs the schematic for the FM, AM related ICs and those look good so my assumption is that those sections are receiving the correct power but I'm not an expert. On a whim I re-flowed the solder on all of the input selector legs and that didn't help either.
Any ideas on what to test next before I randomly start testing components? I can't really tell what is common between AM & FM circuits to test those things explicitly but that is my instinct on where the issue lies.
https://www.hifiengine.com/manual_library/adcom/gtp-400.shtml if you want to take a look at the schematic!