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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE! |
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4th Jun 2008, 9:00 pm | #1 |
Nonode
Join Date: May 2005
Location: Godalming, Surrey, UK.
Posts: 2,593
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1988 NAD 7020e Hi-Fi Receiver from Freecycle repaired
Hello again,
Now for something different to our radio restorations, a repair to a classic budget 1980s Hi-Fi receiver (tuner/amplifier). This was the last but one of the NAD 7020 receiver models built and dates from 1988 and is basically a NAD 3020 integrated amplifier with a digital AM/FM tuner built on. The austere looking NAD 3020 remains the best selling integrated 20w + 20w integrated amplifier ever built, between 1978-1991 millions of units were sold worldwide, many of them in 7020 receiver spec, initially with analogue tuners and later with digital tuners. NAD (New Acoustic Dimensions) is a Canadian (Ontario) company, their kit is designed in Canada, the UK and in the USA and is built in the Far East. I got this Boston/London designed Taiwan built NAD 7020e free from Freecycle and it was accompanied by a matching NAD 502 CD player and a NAD 6325 cassette deck. When I got it home, I tried it out and it was totally dead, only its display lit up. Ron Bryan analysed the fault and then did all the repairs to it, I just gave its metal case a quick clean and obtained service data and later, spare parts for it. I managed to find free downloads of the NAD 3020, NAD 3020e and NAD 3020i circuit diagrams but not the NAD 7020e so I bought one online for $15.95 (£7.80) from user-manuals.com who I think are based in eastern europe. A waste of money really cos Ron had already sussed out the problem using the free sheets by the time it arrived several hours later, and the circuit diagram was not easy to read anyway. There are working voltages indicated at points on the PCB and in the power supply section none was found and a shorted out 0.1 uF 50v disc ceramic capacitor was found in there. That was then found to have caused failures in two transistors, a BD139 and 2SD669A, and a 10 ohm 1 watt resistor further along the circuit. Ron found a replacement 100v capacitor and a new resistor and a couple of similar transistors to replace them, fitted them and the receiver then started to work well. I managed to get replacement original transistors from Cricklewood Electronics which with P&P came to £4.47 and they arrived a couple of days later and were subsequently fitted. Ron also found another unassociated transistor which seemed to be getting very hot even when the amp wasn't working hard - the associated circuits were checked but no faults were found so he very kindly fitted a large heat sink to it and it then ran a lot cooler. This no frills NAD 7020e receiver works really well now and its tuner picks up everything and with very little background hiss on FM stereo. This one failed but generally they have a good reputation for reliability and hold their value well and it was only offered on Freecycle cos its original owner couldn't find a dealer interested in repairing it. The only mild criticism I have of this NAD is that its stereo imaging is not as good as other contemporary budget amplifiers (eg: the Rotel RA-820A and Pioneer A400 which I also have here) but it certainly sounds very good when driving reasonably efficient loudspeakers (Ron's LS3/5As, Mission 700s here) and its 'soft clipping' feature enables it to play very loud without distortion and I'm very pleased with it .... many thanks Ron. My son has grabbed this one for his system, and returned my Pioneer A400 (a better all-round amp IMHO) which needs an overhaul. The accompanying NAD 502 CD player is next in theatre, the bulbs which light up its display have failed. Howard |
4th Jun 2008, 9:08 pm | #2 | |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
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Re: 1988 NAD 7020e Hi-Fi Receiver from Freecycle repaired
Quote:
https://www.vintage-radio.net/forum/...ad.php?t=28717 Paul Last edited by paulsherwin; 4th Jun 2008 at 9:23 pm. Reason: Forgot to paste the link! |
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4th Jun 2008, 9:16 pm | #3 |
Nonode
Join Date: May 2005
Location: Godalming, Surrey, UK.
Posts: 2,593
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Re: 1988 NAD 7020e Hi-Fi Receiver from Freecycle repaired
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4th Jun 2008, 9:46 pm | #4 |
Nonode
Join Date: May 2005
Location: Godalming, Surrey, UK.
Posts: 2,593
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Re: 1988 NAD 7020e Hi-Fi Receiver from Freecycle repaired
Hello again,
Ron has written up an interesting and more technically detailed description of the fault and repair which will be useful for those who encounter a similar fault with this receiver....... The +27V supply failed because C227, a 0.1uF 50V disc ceramic went short circuit. This caused Q511 the 27V regulator (BD139) to go s/c followed by Q507 (2SD699A), the 42V regulator to go s/c as the +27 V supply is derived from the +42V supply. Further damage was prevented by Q507's collector resistor R511 (10 ohm 1W) burning out. The +42V supply is used for the radio tuning voltage and the +27V supply is used as the pre-amp positive supply. The -27V regulator transistor Q505 was getting hot - it was dissipating about 840mW and had a case temperature of about 80 degrees C, which was within its ratings but in my opinon a bit too hot. The currents in the various branches of the -27V supply pcb track were measured, but no excess current could be identified, so I decided to give up fault chasing and fitted a larger heatsink. Maybe the addition of the 10mA of -27V tuner current to the basic amp power supply design caused the extra heating. A 0.1 uF 100V polycarbonate cap (which fitted the 0.3" pcb hole pitch) was used to replace the faulty 0.1 uF disc ceramic without any ill effects. A carbon film 10 ohm 1W resistor replaced the 10 ohm metal oxide film type..... Howard |
4th Jun 2008, 10:40 pm | #5 |
Retired Dormant Member
Join Date: Mar 2003
Location: Bishop's Waltham, Hants, UK.
Posts: 939
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Re: 1988 NAD 7020e Hi-Fi Receiver from Freecycle repaired
Howard,
the 502 problem, is, as Paul says, common. I've had a few off the tip! The repair is simple, and th bulb cheap, but it is the 2 hours labour to change the bulb (the whole thing has to come to pieces) that causes them to be scrapped. Jim. |
6th Jun 2008, 10:56 am | #6 | |
Nonode
Join Date: May 2005
Location: Godalming, Surrey, UK.
Posts: 2,593
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Re: 1988 NAD 7020e Hi-Fi Receiver from Freecycle repaired
Quote:
http://uk.rs-online.com/web/search/s...duct&R=6559592 Howard |
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6th Jun 2008, 12:13 pm | #7 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: 1988 NAD 7020e Hi-Fi Receiver from Freecycle repaired
I bought one of these new and had no problems with it. I only got rid of it about 5 years ago when I got some new speakers which were a bit boomy with the NAD. So I bought a 2nd hand Roksan Caspian which is a bit too 'perfect' and the bass is now at the opposite end of the spectrum. At that point I decided to put an end to my exploration into audiophilia...Peter
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9th Jun 2008, 5:14 pm | #8 |
Nonode
Join Date: May 2005
Location: Godalming, Surrey, UK.
Posts: 2,593
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Re: 1988 NAD 7020e Hi-Fi Receiver from Freecycle repaired
And here's a pic of the failed bits in this NAD 7020e receiver.
Howard |