Pioneer QX-949 in protect mode / no audio

[CapLeaker]

Re: Pioneer QX-949 in protect mode / no audio

while you are in it replace at least all the light blue sanyo caps.
working on a qx-747 now that had distortion and random relay tripping.
none of the blue sanyo caps passed my quick test.
1 was nearly shorted and shoving dc into one channel of the amp.
these same caps are trouble in the kenwood ts-120-140 hf radios too.

This PA doesn't have any blue caps. Mine are gray. I think there are 2 versions of PA's and I think I have the later version one.

[CapLeaker]

Re: Pioneer QX-949 in protect mode / no audio

gray ELNA caps.

[CapLeaker]

Re: Pioneer QX-949 in protect mode / no audio

I've got my digikey shipment yesterday and ordered a bunch of different transistors. Turns out to be a good thing I did that.

The transistor to replace: 2SA726

I've ordered KSA1015GTRA (higher gain ones) and KSA992FTA. Turns out, that the KSA1015GTRA don't have the gain that the 2SA726's had. However the KSA992FTA's are bang on. I am going to try a matched pair of KSA922FTA first.

[CapLeaker]

Re: Pioneer QX-949 in protect mode / no audio

Good news. The KSA992FTA did the trick and the amp is working A1! A little side note: Those KSA992FTA have to be installed backwards. The pin out is the other way around compared to the 2SA726.

[petehall347]

Re: Pioneer QX-949 in protect mode / no audio

easier than having them crossed legged

[CapLeaker]

Re: Pioneer QX-949 in protect mode / no audio

easier than having them crossed legged

that is true...

[CapLeaker]

Re: Pioneer QX-949 in protect mode / no audio

Did an alignment on the FM tuner on that thing aaand? I broke the friggin slug in the discriminator (that large metal can). Here is an easy fix for that. Take a screwdriver with a magnet attached and gently break up the old slug and fish the debris out from the can, turn the unit upside down and blow the hole out with a can of air.

This is important: Note that the IF of the tuner is 10.7Mhz. So you need a slug from a different receiver or transceiver with an IF of 10.7Mhz. In my case I used the slug out of a vintage junked Motorola Mitrek VHF transceiver. There are 2 slugs in that transceiver that are a perfect replacements for the tuner. No shimming, cutting etc required.

[electricboyo]

Re: Pioneer QX-949 in protect mode / no audio

There are some batches of the small TO-92 case transistors in 1970's era audio gear that develop intermittent and sometimes persistent failures after 40 years. Intermittent crackling, popping, and hissing noise is frequently a symptom.

If you identify one such small transistor that failed then it would be wise to search every PC board for other transistors of the same part number and physical appearance.

With electrolytics in 40+ year old audio gear it is a good idea to measure both capacitance and ESR for all of them. Small capacitors may fail more often than big ones because the tiny caps contain only 1 or 2 drops of electrolyte. When it dries up the capacitor become an open circuit.

EB

[petehall347]

Re: Pioneer QX-949 in protect mode / no audio

capacitors are cheap enough and easier to replace with new even if old ones test good . flaky transistors can be found with freeze spray and heat .. some transistors on the hit list depend on the case style whether it might be likely to fail or not ..