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Old 23rd Oct 2017, 1:38 pm   #1
Pioneer4
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Default Quad 405-2 Overheating on right channel.

Hi,

I`m looking for some advice regarding a recently repaired Quad 405-2 which is now getting markedly hotter by approx` 30% on one channel, yet the sound output is the same level in either channel.

The amp has recently returned from a supposedly competent and renowned audio engineer after failing on the right channel due to an apparantly over tightened output transistor which over time had shorted to ground. The amp now works ok but has an imbalance of heat from left and right channels.

After opening the amp to check the work and try to establish what`s causing the overheating I noticed that the two Class A drivers (TR7 & 8) on the overheating right channel have been changed to "1CD4`s" instead of the original MJ15031`s (which remain in the left channel). The output transistors TR9 & 10 have been swapped like for like with MJ15003`s.

Could the use of the 1CD4 transistors be causing the extra heat in the right channel ? Why would this type of transistor be used when it isn`t a recommended equivalent to a MJ15031 ? And more importantly would replacing with 15031`s rebalance the heat output ?

I have not contacted the "repairer" of the amplifier as he tried to charge me 4 hours labour (£180) plus parts to change TR9 & 10 and TR7 & 8 which I think is at least twice what it should have cost and when questioned about the price "spat his dummy"

The fault is definitely the 405-2 as it`s been checked in a friends system with the same overheating issue in the right channel. Any advice would be gratefully received.

Many thanks in anticipation
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Old 23rd Oct 2017, 1:46 pm   #2
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Default Re: Quad 405-2 Overheating on right channel.

Are you sure about the 1CD4 code? I don't recognise it, and Google finds nothing.
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Old 23rd Oct 2017, 1:51 pm   #3
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Default Re: Quad 405-2 Overheating on right channel.

It is not clear under what circumstances it is hotter (quiescent or when playing music, and if so how loud).

And since both left and right channels share the same heatsink, including the drivers, how can you tell if one channel is hotter than the other?

I cannot find any reference to a transistor that is marked 1CD4 - can you post some photos?
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Old 23rd Oct 2017, 1:54 pm   #4
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Default Re: Quad 405-2 Overheating on right channel.

Hi Paul,

Thanks for your fast response.

My apologies, the replacement transistors are 1C04 (similar to T0220).

The heat difference becomes more obvious the louder the amp is played, though still present at low volumes. The right hand side of the heatsink gets as hot as class A amplifier (eg MF A1) when the amp is played at high volume.

The left and right channel boards are at either end of the front heatsink making it easy to detect the difference.
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Old 23rd Oct 2017, 2:00 pm   #5
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Default Re: Quad 405-2 Overheating on right channel.

Hi Craig,

The right side of the heatsink looking from the front gets noticeably hotter when playing music at a reasonable level and becomes seriously hotter than the left when playing it loudly.

The right channel board is to the right of the heatsink and the left board is on the left of the heatsink making it easy to differentiate between the two channels.

The Class A driver replacements are 1C04.
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Old 23rd Oct 2017, 2:37 pm   #6
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Default Re: Quad 405-2 Overheating on right channel.

It's a PNP TO220 power transistor made by RCA. I can't see anything unusual about it, though I've no idea why the repairer selected it in preference to anything else. Googling RCA1C04 will find more info.

http://www.semicon-data.com/transist...a/RCA1C04.html

I can't help further as I have no personal experience with these amps.
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Old 23rd Oct 2017, 4:35 pm   #7
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Default Re: Quad 405-2 Overheating on right channel.

A note on Cricklewood Electronics site says "PNP TO220 100V 7A 40W High Gain. Renumbered by RCA to 1C04. Complement to 40871 (1C03)"

So it looks to be equivalent in every way.

I'd be more suspicious of the channel that is not getting hot when playing at high volume. I'd check how well it is connected to the heatsink. You can reasonably expect a high power dissipation when reproducing music at volume. For the Quad, if the loudspeaker power is 10W, the power transistors will dissipate 40W and the heatsink (which is actually underrated) will get good and toasty.

So check the cool side rather than the hot one.

Craig
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Old 27th Oct 2017, 6:36 pm   #8
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Default Re: Quad 405-2 Overheating on right channel.

Hi Craig,

Thank you for your response suggesting the left channel maybe to blame for the heating imbalance.

With this duly noted I have now cleaned, refaced and reseated both the left and right boards, checked the torque of the four MJ15003`s and, simply for peace of mind, replaced the RCA 1C04 drivers with Motorola MJ15031`s. While the boards were out I also tightened the Philips head screws securing the outer heatsink to the metal face which the boards are mounted on, both of which required half a turn to tighten.

After around 10 minutes of moderate volume I have to report the right side is still becoming noticeably warmer than the left. The two channels are still balanced in their output and quality.

Unless you or anyone else can advise any further possible causes I feel the sensible option is to return the amp to Quad, which is probably what I should have done when the initial fault occured. But after contacting Quad at the time and being advised their lead time is around 4 weeks I decided to try someone quicker (and as it turned out hugely overpriced). Guess I`ll just have to do without the 405-2 for that time.

Although many people could live with the heating imbalance, as the quality of sound output is as good as it`s ever been, surely there`s something electrically out of sync` causing the problem
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Old 28th Oct 2017, 8:57 am   #9
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Default Re: Quad 405-2 Overheating on right channel.

Did you swap the cards over left to right, did you change the input over? You may have some supersonic rubbish down one channel. I would have asked for the price of a new card.
I have worked on many 405's, not a particularly difficult amp.

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Old 28th Oct 2017, 8:59 am   #10
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Default Re: Quad 405-2 Overheating on right channel.

Hi where in Derbyshire do you live as I have a 405/1 or a 303 you can borrow for the 4 weeks

Dave

PS I live in Glossop
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Old 28th Oct 2017, 12:21 pm   #11
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Default Re: Quad 405-2 Overheating on right channel.

Hi All,

Firstly, thankyou Dave for your kind offer to borrow one of your Quads while mine is away in Huntingdon, it`s much appreciated but I have a couple of spare amps to use it`s just they don`t sound as pleasing as the 405-2.

Trev, I`m presuming you mean the left and right boards when you say "cards" ? I have tried swapping the inputs over but makes no difference, but I`m not sure what you mean by "supersonic rubbish" ? I agree the 405 is a simple amp to work on but only when you`re sure which component/s need replacing and as I don`t have access to either a signal gen` or a `scope that is proving to be the problem.

My best guess is that when the right channel output tranny shorted and took out the class A driver it also damaged some other component as previous to the fault occurring the amp`s heat output was always balanced between both channels. So it`s off to Huntingdon with it and time to dust off an old Pioneer SX5580 to fill in for a month

Many thanks for your replies chaps.
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Old 28th Oct 2017, 3:10 pm   #12
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Default Re: Quad 405-2 Overheating on right channel.

Well that chunky Pioneer is a superb stand by! Highly collectable, these are now commanding high sale prices.
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Old 28th Oct 2017, 3:55 pm   #13
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Default Re: Quad 405-2 Overheating on right channel.

I mean high frequencies beyond hearing range. This can cause overheating but to be honest I would not attempt a repair without a good signal generator and a scope these, things can be unstable at times, even changing the output devices can create problems.

Best of luck and regards.

Trev
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Old 28th Oct 2017, 4:16 pm   #14
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Default Re: Quad 405-2 Overheating on right channel.

Thank you for complimenting the 5580 Edward, it`s a lovely old piece of kit. Although not quite up to the sonic quality of the 405-2 it makes up for it in quantity
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Old 28th Oct 2017, 9:03 pm   #15
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Default Re: Quad 405-2 Overheating on right channel.

No, probably not. But I bet if you left it on for a few hours, it would come through for you. Yes, it has loads of power but it also has a very wide Bandwidth.
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Old 31st Oct 2017, 8:58 am   #16
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Default Re: Quad 405-2 Overheating on right channel.

Other problems with the 405 are:

R7 and R8 feed zener diodes to power the input op-amp. They are underrated for power. They dissipate at least 0.37W and the resistors are 0.25W. So at some point one burns out, puts the op-amp hard to one rail, pegs one dumper at the power rail, the crowbar fires and blows the dumper, the driver and then the crowbar. Then the rail fuse blows. The resistors should be replaced with 1W resistors, spaced away from the board by a few millimetres to allow air to circulate.

Electrolytic capacitors associated with the protection circuits are directly above R30 and R31 (560 ohm power resistors). These run hot, and cook the electrolytic. These are ROE epoxy potted caps, and will be badly discoloured and cracked. When replacing, the caps should be soldered to the track side of the board to keep them away from the heat.

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Old 1st Nov 2017, 6:32 pm   #17
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Default Re: Quad 405-2 Overheating on right channel.

There are two professional companies which I would trust for Quad 405 repairs and updates. The first and most relevant here possibly are QUAD THEMSELVES, who will repair to basic spec and continue to have a good general reputation for basic repairs and refurbs.

The other company I've used for update kits and this is Dada Electronics (In the Netherlands) who have a mine of info on their website. They can supply refurbished boards and kits to update old ones and these seem sensibly researched and thoroughly tested so as not to upset the basic original designs.

I appreciate there are good engineers here well able to deal with repairs, rebuilds and so on, so the info above may only be useful for reference. The 405 circuit went through a number of changes in the early days (different layouts from memory of seeing them) and my time with the 405 series 2 'official' version was using 'issue 7' main boards. I believe Quad may still supply their own series 2 boards and I 'think' they're now 'issue 10.' The Dada equivalent uses selected rather than general purpose parts and possibly a posher op-amp, which is in the signal path in this amp rather than alongside it as in the 306 and 606 family I gather, so a tiny sonic difference may be heard.

Apologies folks, I'm going off into audiophool territory, but in this case I think it's worthwhile doing some research. I've owned and fondly remember two 405-2's in my time and am a huge fan of the 606 onwards models, well fettled examples of which apologise to nobody at any price level in my experience. The 405-2 is potentially a lovely and generally reliable amp, but I feel that some components of the period weren't quite up to it, so careful checking of components and updating with good sympathetically chosen modern ones should pay dividends to this endearing compact 100 Watter.
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