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About mbz

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  1. Some basic things first. Switches are a problem with vintage gear. Try different inputs, ie, connect your source (CDP?,,,) to TAPE 1 PB, then TAPE 2 PB, then TUNER. Same behaviour? Hit the high filter and mode buttons, no change in sound level? Try headphones. I'd prefer that you took the amp to a tech rather than providing guidance, lethal voltages inside, I don't know your skill level... Below, I've marked what I think is zeners D302,3. Measurement of Vdc at the highlighted point, expect +/-20Vdc, repeat for other diode. If both results are zero then I've made an erro
  2. Most probably power supply to preamp is down. Preamp is NJM/JRC4558 based. Either the +ve or -ve supply is down, this would affect both channels. Since you are getting some audio means the protection relay has engaged so not a dc offset issue. Both channels same level would mean unlikely to be dirty relay contacts. Simple job for a tech to check the power supply. The supply is unregulated/fed directly from the main caps. Possibly failed zener D302,3 or leaky cap C301,,,4 or R301 open. Service manual available on hifiengine. Maybe open the unit up and post some hi-res pix of component side
  3. mbz


    Thinking real hard about this, downside is a 3hr return trip from melb, upside is that it's a RX-V1 for nix. Those that poo-poo AVR's have not had a listen to one. Probably just needs the power supply to be refreshed(recapped?)
  4. Perform basic health check before doing anything, eg, check for audio for the different sources. Dirty switches is a big problem area in vintage. Also should check bias and dc offset stability both when cold and then hot-ish. Then feed it some good input and have a listen. Google audiokarma cr620, plenty of rebuild threads to give you an idea. While there are known problematic transistors, some guys replace all silicon, probably for improved reliability. Not sure I agree with replacing all. Ask your tech if (s)he can do a tuner realignment etc... does he have the necessary tools, I
  5. Abnormal DC voltage (16%x5V=0.8Vdc) at output stage. Certainly repairable however requires some experiance to track down.
  6. Reads a bit like a degrading power supply or degrading transistor and dc offset. The 5V/12V regulated supplies are known to cause problems, sometimes the supporting caps get tired, sometimes the regulator. Suggest try reading the diagnostic information, need to execute the following sequence, ie, while holding down the A/B/C/D/E and preset/tuning key, press the STBY/ON key. Record the information displayed, expect something like, PS PRT:nnn DC PRT:nnn OK, it's pre-hdmi so not very valuable, but these higher end RX-V's sound reasonable if you
  7. Yamaha have always tried to do the right thing, even their AVR's are well designed and use quality parts (excluding entry level). I'm into vintage, like the CA-1000/800 and the CA-2010/1010, the "newer" CX-1000 pre is a keeper. Tempted to try something from the A-/AX series, imagine it all sounds good.
  8. Welcome, hope you are talking about vintage NAD. While the modern amps probably sound better they are a PITA to work on, explains my preference for vintage, maybe 3140, 3150. Not a big fan of the PE series, I've got a 2700 to fix, it went into meltdown.
  9. Welcome, you should fit right in with keywords like MF, LP12, Paradigms, tube and DAC/lossless... Sadly I'm into vintage (due to insufficient funds) so I get to sit in the corner. All jokes aside, try not to take things too seriously, have a laugh, get some great ideas, many people to help out and enjoy the music.
  10. The OEM connectors are workable, unlike the ones on the KA-7100 et al... The link from muon contains good examples. I opt for the faux gold plated items from the bay (china) $8-12 for set of 4 which is strange considering I spend hours refurbishing amps and then cheapen out on the spkr posts! Time for a rethink? Suspicion is that most things from china are fake including the high priced posts, exception would be consonance...
  11. Sorry, poor effort. Assuming you tested for audio at the pre-outs. The amp is fully discrete (no STK's) FET in power amp stage, no boutique parts in the pre. Should have been able to localise the problem in 15minutes with a scope. Possibly a problem with dirty switch contacts. Connect your source to another input, eg, TUNER. Also try phono stage. You could also try working ALL switches and note any changes to failed channel.
  12. The sucker bet is the main filter caps, however there is some merit in this case, considering the loss of bass. Would be nice to confirm hum is rectified AC (100Hz) rather than mains hum (50Hz), mobile phone app, freeware(audacity) and others can measure. PM me with your location, I'm in W Brunswick, happy to replace main caps only (parts cost only). This is a punt, no guarantee. If hum is 50Hz then need to look elsewhere.
  13. Check out the pheonix site for all things PL https://forums.phxaudiotape.com/ The unit probably needs main caps replaced, these were undersized from original. The circuit boards are not great, don't tolerate re-work well. If you can get it working normal you won't need another power amp. Strongly advise to fit an after market spkr protection kit, basic units can be had off the bay for about $20-, maybe another $10- for dedicated paower transformer. The PL400 Series 1 has a power up "race condition" that may mean rails voltage (+/-80Vdc?) being dumped on
  14. Looking at a marantz 2285B where both the active and neutral are switched via p-on/off switch. Both lines have snubber caps. The switches in these units are prone to failure so maybe switching both is an idea of extending the switch life. Have implemented a triac for switching. Anyone with other examples of both active/neutral switching?
  15. The AU-505 is a nice one, considered something of a "giant killer" (bang for buck) on audiokarma who have several nice threads showing upgrades etc, they include the blaxandall diode and a cap mostly copied from the 555A/555(?) I run my fully refurb'd unit through some moderately efficient vintage altecs (102dB?) for background listening. Mine had a hum issue which was a pita to track down. Hum persisted after converting to a star GND, noticed one of the tone caps was resting on the p-on lamp, moved cap and all good (doh!) Not good about the earth pin, like you say, thrill seeker..
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