Aboutcleggsan Expertise Consumer Electronics of all kinds. Audio, esoteric audio systems and components, video, tv. Digital equipment for consumer use. Ham radio and automotive electronics. Note: I give advice on tv repair based on general consumer electronics engineering experience but I am not engaged in actual repair of sets. MAKE SURE YOU GIVE THE MAKE AND MODEL NUMBER AND AGE OF THE SET.
Experience Electrical Engineering; recording, broadcasting, design, international standards, tv and radio theory and practice.
Organizations FELLOW of AES (Audio Engineering Society)
Senior Life Member of IEEE (Institute of Electronic and Electrical Engineers)
International Consulting Organization
Publications IEEE Spectrum
Various Consumer Electronic publications
Education/Credentials BSEE
MSCS
MBA
Awards and Honors Famous Engineer for Digital Audio
Question I have a Pioneer SA-7500 amplifier that has no output. I have ran a signal into the amp and can tell that the output section is not getting any signal. I have narrowed the problem down to the tone selection board. The signal disappears there. I have tested most of the components on the tone selection board and did find 3 leaky caps and 1 cap that was acting wierd, so I replaced it. I don't have a service manual, not sure if you know of any good free sources for one (I'd rather not have to pay for it). I'm not sure of the history of the problem as this was the condition of the amp when I got it. This amp is a classic that I'd like to get running again. Any help that you could provide would be greatly appreciated. Thanks Much!
Arne
Answer You might try http://fileshare.eshop.bg/ and also do a google search; there are a few places that post schematics and related documentation.
This is a classic amplifier and is a lot of fun. It would be a great sounding unit, for sure.
If you know how to trace the signal through the various stages you are home free. But they are tricky and you must know what you are doing. For example, one of my correspondent chased the signal as you are doing and found it could not get past about the same place that you are talking of; it turned out the tape monitor switches were on and the signal couldn't get past that point until the monitor switch was thrown and the problem turned out to be in an entirely different location. So, just be careful and sure of your steps.
Another good way is to inject a signal into the top of the volume control to see if it will make it through to the end. And if that doesn't make it, go to the predrivers and inject a signal. In other words, sometimes signal injection is more sensible than tracing through the input. Be sure to put a big capacitor in between the signal source and the injection point so you don't run into a dc offset problem.
Also, it is best to work with low level signals so you don't accidently overload the outputs or throw the bias off enough to send the outputs into dc burn up.
Also, with no load on the outputs measure the dc voltage at the output terminals. If there is dc, it means something is wrong with the outputs; like one of them is shorted out. Or, if the dc is okey, it could be both outputs could be open circuited.
If you can get to the bottom of the boards you can look for hairline cracks; a big problem with older audio products. If you find one, you can bridge the circuit over with a short jumper soldered between the two circuits.
Happy hunting. Let me know the outcome. I love these old audio amplifiers. Once you get them working they will run for years and years.
