DC Offset ?

[Cosmic Charlie]

Hi, to all. I have a question about DC offset. I aquired a Pioneer SX-580, that has no sound, I replaced the Darlington powerpacs, hoping they were bad, still no sound. I cleaned all the pots and switches with deoxit, still no sound. All the lights iluminate, while turning the tuning knob the tuning meter moves, the stereo indicator lamp lights, I check DC offset with the A B speaker buttons in I get 0mA, with the buttons not depressed I get around -1.4 to -1.8, isn't that the opposit of what I should be getting? I thought I should get 0 with buttons not depressed and a reading when the buttons are pushed. I purchased a service manual, but I'm not real sure about reading it properly, as I am new at electronics, but want to learn. I can read plumbing and carpentry prints, but I'm nearly clueless with the electronics. I have been studing the schematics, and am begining to decipher some things. I've checked voltages at various spots on the board, most are right on some are close some are way off. I don't know how close is close enough + or - (tolerance). Can someone advise me where to look or where to start. I know my receiver is a low model, but it is probably a good one to learn on. I am willing to take all suggestions and ideas happily. If anyone has experence with this model or others, I would love to hear from you. I'm new to AK but have learned just from searching and reading the threads from the excellent folks that frequent AK. Thanks, any ideas CC

 

[hpsenicka]

bias adjustment?

Does the service manual describe how to check and adjust bias?

Pretty basic stuff, but I'd start there.

 

[EchoWars]

Check all supply voltages first!! That means the regulated and unregulated voltages. Are they good?

If you don't have the voltages coming from the supplies, all bets are off.

 

[Cosmic Charlie]

EchoWars, thanks for the reply. Please excuse my ignorance, but I don't understand where to measure the supply voltage, regulated or unregulated. I'v been reading and rereading my manual but I can't find anyhere that tells me where or what the measurements should be or where it should be taken. I'm sure they are there but I cant seem to locate them. I'v checked all of the semiconductors for voltage, some are low some are high, but they all read something. Is the supply the leads that come from the power transformer?, I cant find a voltage requirement for those either. I'm starting to think my manual is missing a page or two, but it's probably just me. I know the search button is my friend, we've been getting aquainted. Well if you have the time please advise. I was wondering if maybe the problem lies in the FET gate circut that they employ in this model that serves as a muting circut as opposed to a relay. I thought that if a componant failed in that circut it may silence my amplifier section. Thanks again and I understand if you don't want to get involved with an untrained person with the desire to fix a $25 receiver, but I already have $40 into it. Any and all forum member suggestions are welcome and greatly appreaciated. Remember I'm a newbie. CC

 

[EchoWars]

It really has nothing to do with not wanting to help...hell, if you were local, I'd have you come over and I'd put your @ss to work fixing it yourself, pointing out things to check along the way while we quaff a Guiness or two. As it is, through email, forum postings, and whatnot, this is very very difficult and time consuming (cause I can't type for chit) and trying to steer someone in the right direction through 'remote control' is goddamn difficult. So I hope you understand why a crash course in stereo repair is unrealistic.

Manuals will not 'tell' you where a voltage needs to be measured...it's up to the tech to spot the power supply, determine the voltages generated, and figure out where best to check them. I know that, for instance in the military, manuals give step-by-step procedures for this and that...no such animal for stereo gear. Essentially MOST gear is simple enough that a schematic pretty much tells the tech about all he needs to know, notable exceptions being things like tuner alignment.

If simply having a manual isn't enough to get you kick-started, perhaps the repair is out of your league. Got a friend who's electronically inclined? If not, I guess you'll have to decide if you want to have someone else tackle it.