405-2 usual problem ??

[Karl W]

Well after years of having oriental made so call high end hi-fi I bought a 34 & 405-2 combo. Problem is that after first "run out" as it were its all gone wrong. First use was very good, then following night got heavy crackling on left channel . Then used again after a week and really heavy crackling and signal loss. Tried them again after a week and no output at all on either channel. After few minutes of leaving amps on then getting some output but very intermittent and crackling again. I'm aware of age and problems on these, took amp boards out and no evidence of over heating on circuit board but lots of heat sink compound round heat sink and thumb marks make me wonder if someone has had a go at power output transistors before. Where do I start ??

[Zen Mod]

with pictures

[Karl W]

Tell me what pictures will help and I'll gladly post.

I tried amp again tonight. I left them on for 10 minutes then played CD through them and although it was crackling a fair bit, they did seem to drive speakers OK, albeit very dull mid range... so letting the amp "warm up" seems to make a difference from cold but still pretty awful !

[Tajzmaj]

Hi
If I'm correct we are talking about Quad 405-2 and it's preamp? First you must find out which one causes this crackling. Preamp or pwr amp. Second thing is that this can damage your speakers so be care full.
If there is nothing burnt than it cause probably some dry cap. In 405 there are 2 caps on psu, And 3 electrolytic caps on each board. They are all cheap and worth to replace because it gets damn hot in quad's closed enclosure. But there is more. When i bought my 405 there was broken input 0,68uF input foil capacitor. It was broken literally. On leg falls of !!! So check it out.
But first find which unit is cause of noise.
After you repair everything you must renew thermal compound. Clean old and put on lots!!!! of new.Which output transistors are there anyway? Are all the same? If not then is good idea to replace all 4 of them with MJ 15024. They cost around 2,5€ where I live so 10E for stereo amp. And check rectifier bridge because it is underrated and exposed to high peak currents when you fires amp on. Quad has no soft start.
You can also post some pictures........if you think that may help......
Good night

[tunneldiode]

Do you still get the crackling with the 34 unplugged, and just the 405 connected? I suspect you will.
Most likely dried-up electrolytics on either the amp board(s) or PSU, likely both.
C2 and C5 are usual suspects, but they are probably all past their best.
Also check R7 and R8, both 3k3, replace them anyway (they are a trouble spot on these amps) use at least 2W resistors.

I use a 34 and a 405-2 myself, very pleased with it.

[JT23456]

I took my Quad system out of storage - been 6+ years - and tried it. The 405-2 amp with the 34 preamp NOT connected so no audio input to it - the amp crackles and pops in one channel quite loudly - disconnect that speaker and I can hear quite faint crackles and a bit of 60 cycle hum in the other channel. Question is - I look on eBay for power supply caps 10K uF 63 v and prices are all over the place - what quality is needed vs wished for here - I'm retired and just trying to get this working.

[Tekko]

Get a known quality brand like nichicon or cornell dublier or nippon chemicon similar.

Stay away from the cheapos with weird names.

[Tajzmaj]

If I'm correct I install those in my 405.....
Regards
EPCOS|B41456B8229M|CAPACITOR, 22000UF, 63V | Farnell Republika Slovenija

[genver]

Look at Home
They usually have all the parts you need for an upgrade and they will be happy to give you all the information you need. Ask for Stefaan Verdonckt.
Good luck.