oh man, just please stop.
Let a qualified tech look at it or you'll do even more damage.
Really.
Best,
E
Let a qualified tech look at it or you'll do even more damage.
Really.
Best,
E
Filter capacitor issue
I've been a member for over 10 years and have never posted anything on here so please bear with me. My main system is a Bedini BA-802 solid state amplifier, Music Hall Maverick SACD player, Magnepan MG2.6r speakers, Denon DP-59L turntable with Micro Acoustics MA-2002e cart but I have an issue with a Marantz 2220b receiver that hopefully someone on here can help me with. I bought the receiver with plans to do some simple upgrades ie: replace some caps, etc. and resell it. I When I changed out the large filter caps I inadvertently installed the cap for the left channel backwards. I put both negative terminals on the buss bar. The right channel cap is installed with negative on the buss bar and the left channel cap should have been installed with the positive terminal on the buss bar. Needless to say the left channel cap got angry and blew it's top. After realizing my error I put in a new cap correctly but now the main 2 amp fuse is blowing after about 20 seconds. I'm thinking I may have damaged the power transistors or smaller transistors on the main amp board. The service manual also says to check the thermistors on the amp board. I'm not an electronics tech but my brother is and has been teaching me some basics over the last few months. Unfortunately he's not here to help me out this week so if anyone has any insight into this it would be much appreciated. Thanks in advance, Eddie D.
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I'm kinda with Erik. Filter caps can blow your fingers off. That just isn't a mistake you make. I've looked over the schematic. There are no left or right channel filter caps. (You really should have known that before warming the soldering iron.) That capacitor arrangement references the output of a single rectifier to the center tap of the power transformer secondary and chassis ground to create a bipolar power supply. Your mistake lifted that ground and put the full output of the rectifier onto one rail. Something seems to have failed closed, and that's what transistors tend to do. My guess would be drivers since the small signal devices are getting their power from the regulated supply on a totally different transformer secondary. The first step to trouble shooting would be to pull the outputs and test those using the diode function on a DMM, and if they check good, pull the driver transistors and check those. You can't check them on the board. All the signal path transistors are matched pairs. They must go in exactly where they came out, pin for pin. You've got a cell phone. Take lots of detailed pictures. Triple check. Also check the H717 through H720 diodes. Don't try powering on the unit again until you've constructed a dim bulb tester. If you don't know what one is, Google it. They're easy to build and one would have probably avoided this altogether. |
Skymunky57, Capacitor blew the top because of increased pressure caused by rapid temperature increase, caused by excessive current. Most likely rectifier is damaged (causing short) possibly without damage to rest of the circuit (you might be very lucky) - relatively inexpensive repair, but I agree 100% with Eric - wait for your brother. Even if you have basic knowledge - two heads are better than one. You probably have already big mess from blown capacitor. Capacitors have fuses in form of rubber plug or pre-cut top to prevent dangerous explosion but it is not always 100% safe. |
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@skymunky57 Despite how it was delivered, I would heed the advice of some you see here. On something like this, where the final product isn't going to be worth all that much anyway, you can really get in over your head quite quickly due to its complexity! If the power rectifier was damaged, the repair might be fairly simple- just replace the rectifier. If the output section was damaged because one rail was shorted by the backwards capacitor, then at that point you have to consider whether the unit is worth repair! That is because its very likely both channels are damaged, and output transistors and their driver transistors that actually work (and aren't counterfeit, which is very common these days) can be rare and expensive since they are likely long out of production. You will want to have identified all the damaged semiconductors before ordering any of them. In addition, a helpful tool is something called a variac, which allows you to start the AC power from zero volts and slowly raise it until you get to full 117V. Such a unit should have an ammeter, so you can see that you are drawing too much current before something is damaged. I would at the very least wait until your brother is about. |
I'm with kosst_amojan. It's impossible to know what is wrong without a systematic trouble shooting strategy. There could likely be multiple problems that must be addressed before the unit is powered up again. I've made that mistake in the distant past as a newby, so don't feel too bad. Regardless of what others have said, if you like the unit, go ahead and repair it. |
I've never seen mention of buss bar in solid state circuit design, only in reference to service panels which go on the outsides of homes. But to your query, I hope you can create a safe working environment for yourself before doing any more work. Also, if you love electronics, there are plenty of technical schools and colleges that can provide safe environments for building smaller versions of the things that add up to what you are working on now, over 2, 3 or 4 courses. Some of the helpful suggestions above are probably well-intended but I would take the capacitor's 'discharge' as a heavenly sign and probably junk or store your science project until help arrives. You can easily die if the testing method is "hoping it doesn't blow up when plugged in" and you didn't mention if you were working with any isolated power supply, GFCI if you were wearing eyewear, or were near other people when doing this. Any other attempt for knowledge transfer couldn't cover the one or two-hundred pages of information you will need to protect yourself and the potential buyer, especially the potential cost if a buyer gets hurt. "Recapping" is probably the worst point to start learning especially if you are not familiar with an overall circuit design, self-preservation, (i.e. no channels at this point) and what each piece does and what specifications to "recap" with. |
There's a Marantz 2220b, in good working order, currently on Ebay for $300 (BIN $400) https://www.ebay.com/itm/173698186290 You may want to consider it for parts or replacement |
There is no room for guesswork in electronics. If you can't explain everything in that schematic diagram find somebody else to do it. If you don't have a schematic and better yet a sevice manual don't even try to do the surgery. Some little detail may not be obvious to the untrained eye which may cause you grief. |
To the OP, obviously your brother did not teach you enough, or you did not learn enough from his teachings. The fact that you thought you can do all this work, with the intent to selling it ( probably to profit ), I am glad the piece did not go into the home of a prospective buyer of yours, as you likely would have stated to this buyer, " it was upgraded by an experienced technician ", which certainly, at this time, you are not. As far as the unit, I would wait for your brother to return, take a look at the piece, and together, determine a fix. Always....Enjoy ! MrD. |
Damn.... Am I the only one who wants to see this guy dig back into this thing and fix it? There's nothing wrong with it he can't diagnose with a DMM. I'd like to see him succeed! If the guy needs the whole manual for it I'll post a link. I want him to learn and succeed. Maybe this one will be a financial loss, but I hope it's not an educational loss. Keep at it man! |
As long as it’s not sold on to some poor schmuck, go for it. While I am not taking a dig specifically at the OP, you can’t just pick up a service manual and fix electronics. It’s a disservice to those who have gone to school and taken exams and/or spent a lifetime honing their craft. Imagine your doctor doing the same thing? Or a pilot? Ebay et al are bringing out the fly-by-night element who are out of their league. |