Need guidance repairing vintage 31 band EQ - Page 1
Forum section: electronics / repair

author: miguel
author_rank: Newbie
timestamp: July 15, 2016, 10:22:38 pm
content: Hi everyone i am a huge fan of the youtube show , i am about to graduate from mechatronic engineer recently a friend of mine asked me to take a look on his EQ so i checked it turned out to had a shorted out power suppy 2 7818 regulators where bad also 2 bad fusesRepaired that and i was happy PSU worked tested voltages -18v 0v 18v everything good (isolated)But when i plugged the Psu Back to the system Fuses POP again , took out the next PCB(input side) , changed 2 small capacitors noticed 2 traces missing so i jumped them with wire , still have a short somewhere i think it may be inside the input relay buy not sure , maybe a diode any suggestion , it also has 2 5532 op amps witch may be dead (don´t know how to check no visual damage)Almost forgot on the voltage input for this pcb i have (-v 0v +v) -v and 0v gave me short circuitThanks a lot , i have theoretical but no real practiceThe old beasthttp://www.bhphotovideo.com/c/product/493335-REG/Klark_Teknik_DN360_DN360_Graphic_Equalizer.htmlService Manual Page 12 is where i isolated the problemhttp://bee.mif.pg.gda.pl/ciasteczkowypotwor/stage/Klark%20Teknik/KlarkTeknik-DN360%20equal.pdf

author: miguel
author_rank: Newbie
timestamp: July 15, 2016, 10:36:43 pm
content: Damage Pictures

author: Andy Watson
author_rank: Super Contributor
timestamp: July 15, 2016, 10:38:49 pm
content: Could be many things!When you replaced the regulators did you check that their tabs where electrically isolated (if necessary) ?Can you disconnect the output of the power supply whilst it is fixed in position and power it up?If you are suspecting a short on the processing section I would first focus on the capacitors across the power supply rails - especially electrolytics and tantalums (if present).

author: miguel
author_rank: Newbie
timestamp: July 15, 2016, 10:55:58 pm
content: Quote from: Andy Watson on July 15, 2016, 10:38:49 pmYes regulators are isolated and PSU works alone voltage outputs are spot on and no blown fuses problem is when i plug the jumper wires to the back (input) Pcb seems the problem started here

author: Andy Watson
author_rank: Super Contributor
timestamp: July 15, 2016, 11:11:21 pm
content: Quote from: miguel on July 15, 2016, 10:22:38 pmWhat is the back story? How did this unit become faulty?When you said the traces were missing I assumed they were associated with the power supply but, as far as I can tell, those tracks connect the input and output sockets! Has somebody connected this unit to the speaker output? It looks like the unit has had "significant" power pushed up its audio input sockets!

author: miguel
author_rank: Newbie
timestamp: July 15, 2016, 11:21:30 pm
content: Quote from: Andy Watson on July 15, 2016, 11:11:21 pmYes they go to the input on one of the channels , i assumed somebody connected a amped speaker signal in , but the owner didn´t know for shure thanks

author: Andy Watson
author_rank: Super Contributor
timestamp: July 15, 2016, 11:30:09 pm
content: Quote from: miguel on July 15, 2016, 11:21:30 pmIf that is the case there is a good chance that IC2 (or other chips that connect with the I/O sockets) will have been destroyed. If you are lucky the damagemightstop there. Do you have an alternative variable power supply to drive the positive and negative rails? - If you do you could try driving a few hundred milliamps into the board and look for the chips that get hot.

author: miguel
author_rank: Newbie
timestamp: July 15, 2016, 11:37:34 pm
content: QuoteI can use one at school but everyone is on vacations , i think i will replace anyway since they are not expensive i just hope relays aren´t the problemi took the opamps out and pins 4 and 5 give shrt on both weird

author: miguel
author_rank: Newbie
timestamp: July 17, 2016, 01:50:01 am
content: I am so stoked i found the problem and it turns on now , it turned out to be an Ic(DG308ACJ) witch is Quad SPST analog switcheshttps://datasheets.maximintegrated.com/en/ds/DG308A-DG309.pdfwhatever that means it was shorting both -v 0v and +v once i removed it short was gone , i got lucky took all ic´s off since they arre on sockets thanks good and started putting all in until one the last onegave shortthanks for the help