JVC A-X500VB amplifier - Page 1
Forum section: electronics / repair

author: Skylineview
author_rank: Contributor
timestamp: May 07, 2019, 12:21:56 am
content: Has anyone here had any dealing with repairing the JVC A-X500VB amplifier? Mine has been acting up for some time and just today decided to not work. I can't switch inputs, I get no graphic equalizer, but the speaker protect relay does click in. I can only imagine the issue is with the digital part of the amp.I'm just wounding if there are any "common" issues with this model that I can check. I'm waiting for the download link for the service manual I just purchased.Any help is appreciated.ThanksClay

author: coromonadalix
author_rank: Super Contributor
timestamp: May 07, 2019, 10:13:10 am
content: With the service manual, youll be able to check supply lines, start with any power supply section(s) you haveIf you have protection kicking in, you may have dc voltages on the speaker output, check that, put fixed resistors like 8 ohm 25 watts 16 ohms etc .... measure with dc voltmeterAll your problems maybe related .... dont change anything, troubleshoot firstI have the service manual from hifiengine, but many oher fakes downloads sites.

author: Skylineview
author_rank: Contributor
timestamp: May 08, 2019, 10:53:14 pm
content: I also forgot to mention that when it was acting up I could usually give it a few tapson the side of the case and it would usually start working correctly again. I have the service manual, but it doesn't seem to be much help, granted I am new to all of this repair stuff.I'm trying to get it apart to start looking for bad solder joints, in the boards I've pulled so far, I've been unable to find any thus far.

author: Skylineview
author_rank: Contributor
timestamp: May 08, 2019, 10:55:30 pm
content: To clarify the protection doesn't click in, rather the relay clicks as usual, Im unable to select input, adjust the EQ and I don't get any of the spectrum analyzer display.

author: PKTKS
author_rank: Super Contributor
timestamp: May 09, 2019, 01:36:23 pm
content: TAPs indicate most likely bad cracked or cold joints.You definitely will use an optical assist to do that evensome sort of magnifying glass ... all validNot easy to spot sometimes and very time consuming jobSome examples attached (they are indeed hires but croppedand shrink to fit the allow. size)Paul

author: mzacharias
author_rank: Frequent Contributor
timestamp: May 09, 2019, 02:15:12 pm
content: Yeah - I would say bad solder at the FL tube on the front panel. Mainly at the filaments on either end but possibly others along the entire row.

author: Skylineview
author_rank: Contributor
timestamp: May 09, 2019, 10:44:55 pm
content: Okay, I will find my optical loops and check carefully.I assume that the bad solder joints would also cause a no input select problem as well, correct?If posting the manual helps, I'll post it.

author: mzacharias
author_rank: Frequent Contributor
timestamp: May 10, 2019, 02:32:24 am
content: Quote from: Skylineview on May 09, 2019, 10:44:55 pmNo, but bad tact switches are also very common.

author: Skylineview
author_rank: Contributor
timestamp: May 11, 2019, 01:14:31 am
content: I've not had any issues with the tact switches, they have always worked fine for me. Basically it would drop out of the input I had selected and would then cause a no output situation, I could tap it on the side a few times and then it would miraculously come back up and start working. The FL display worked flawlessly, unless the input select issue happened. Maybe I'm over thinking the entire thing and looking too broadly and need to narrow it down to just around the input selection chip.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 11, 2019, 02:53:01 am
content: on image 7 is this a scratch or a fissure in the pcb layer ??

author: mzacharias
author_rank: Frequent Contributor
timestamp: May 11, 2019, 12:59:04 pm
content: Quote from: Skylineview on May 11, 2019, 01:14:31 amI would add however, if the display is inoperative, you might press a given tact switch and see no response, even if it worked.

author: PKTKS
author_rank: Super Contributor
timestamp: May 11, 2019, 02:42:36 pm
content: Quote from: coromonadalix on May 11, 2019, 02:53:01 amOn that PCB i posted that thing is CORROSION under the solder mask itselfIt took me quite a while to scrap and apply a new UV repair mask on that.the trace underneath that became a garbage corroded stuffOther cracks mostly done with new solder blobsPaul

author: shakalnokturn
author_rank: Super Contributor
timestamp: May 14, 2019, 08:46:49 am
content: Most likely bad solders, start by any large and/or hot component those are the ones that stress solders fastest. (Regulators, power transitors, >1W resitors, VFD filament)Then there's the interconnect, the wires pull on the PCB side of the connector and weaken the solders there too.Also look around the 2 large capacitors, this model looks like it may suffer from glue corrosion. The glue used to stick the capacitors can corrode components that have been covered with it, not always obvious and can cause unexpected faults.Make sure you don't destroy one of those Super-A voltage amplifier IC's, I'm sure they're very hard to find now.