Bush DAC 90 shorting electric - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Station X · 12th Sep 2019, 1:35 pm

See posts #10 and #12.

Graham G3ZVT · 12th Sep 2019, 1:46 pm

Hi there, I edited this picture of my set indicating which wire to cut to disconnect the most likely faulty component, but I was reluctant to post it in case the set (not to mention you yourself) got hurt. In the light of everyone else's good advice here it is

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The red X marks the spot, your wire will connect to the solder-tag above, just cut the wire, no real need to replace the capacitor, the set will work without it.

Trivial, you might say, and you'll be right, except for one thing, you need to access the underside of the chassis, and that involves removing the three knobs (warning, they don't just pull off, they each have a screw that must be slackened) and unscrewing the nut & bolt securing the round aerial coil from the side of the cabinet, then you can withdraw the chassis and work on the other side.

This doesn't address the fact that some other capacitors (particularity one) really need replacing if they are original, but there is a very good chance it will get your set working as before.

TonyDuell · 12th Sep 2019, 6:44 pm

An aside if it is an RCD that's tripping...

The incomer ('Main Switch') in my house is an RCD. A couple of times when I have had a serious overcurrent fault live-neutral (i.e. earth was _not_ involved), it tripped. Once was when a fillament light bulb failed, the other is when I did something stupid on my workbench.

My guess is that there are slight inaccuracies in the differential current transformer in the RCD so that a large overcurrent in both live and neutral will generate enough signal in said transformer to trip the device. To be honest I don't really care, if I have a short across the mains or similar I want something to trip and cut the power off, I don't really mind what trips.

This could explain why a DAC90 (no earth connection) with a shorted mains filter capacitor could trip an RCD.

JUSTDAMO · 12th Sep 2019, 9:29 pm

Quote:

Originally Posted by Station X

The fault's in the radio then. Snip out the cap as described in post #11. It may not be the faulty, but without test gear there's not much else you can do apart from making a careful visual inspection of the wiring to the voltage selector dropper resistor etc.

Gentlemen I congratulate you and thank you!!!

Snipping the cap worked and its running again thanks again for all advice given.

PJL · 12th Sep 2019, 11:15 pm

Don't use the set as other parts will fail, just sell it as it is now. It needs to be properly serviced before the power can be left on for long.

Tractionist · 13th Sep 2019, 9:29 am

Quote:

Originally Posted by PJL

Don't use the set as other parts will fail, just sell it as it is now. It needs to be properly serviced before the power can be left on for long.

Amen to that!

Sideband · 13th Sep 2019, 1:57 pm

The capacitor that shorted out was a warning! All the other capacitors are of the same age and likely to do the same thing (to a greater or lesser degree). DON'T USE IT. Sell it as unrestored but working with a comment that it should be fully serviced before use.

G8UWM-MildMartin · 14th Sep 2019, 2:08 am

If you want to continue to use it, the other posters are right: after over 70 years it really will require some further attention to work properly and avoid damage.
A post in the "Repair and Restoration Services Wanted" section here would be worth a try if you don't want to do it yourself after reading the numerous threads here covering this popular model.

kalee20 · 14th Sep 2019, 11:15 am

Definitely.

This capacitor failed and fast-fried your fuses.

There is another capacitor which is likely to have failed, but instead will slo-cook two of your valves, which are more expensive than fuses and moreover are a finite resource!

Sideband · 14th Sep 2019, 1:03 pm

Quote:

Originally Posted by kalee20

Definitely.

will slo-cook two of your valves,

....and the output transformer!

Station X · 14th Sep 2019, 1:27 pm

I think we've got the message. Let's hope the OP does!

emeritus · 14th Sep 2019, 9:45 pm

The mains capacitor had failed S/C in the first DAC90 I was asked to fix. I think that capacitor was provided to filter out the hash you could get on DC mains from generator ripple and/or commutator brush sparking from DC motors. Removing the capacitor from mine had no obvious effects, and in Chelmsford it was even possible to get noise-free reception of a couple of continental medium wave stations in daytime by turning up the volume to max, whereas my state-of-the-art Sony portable with its PLL tuning and all, was completely silent. That was in the 1990's when there were still plenty of AM stations broadcasting. I did fit a replacement capacitor once I had found one before returning it.

12th Sep 2019, 1:35 pm	#21
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Bush DAC 90 shorting electric See posts #10 and #12. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

12th Sep 2019, 1:46 pm	#22
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,724	Re: Bush DAC 90 shorting electric Hi there, I edited this picture of my set indicating which wire to cut to disconnect the most likely faulty component, but I was reluctant to post it in case the set (not to mention you yourself) got hurt. In the light of everyone else's good advice here it is The red X marks the spot, your wire will connect to the solder-tag above, just cut the wire, no real need to replace the capacitor, the set will work without it. Trivial, you might say, and you'll be right, except for one thing, you need to access the underside of the chassis, and that involves removing the three knobs (warning, they don't just pull off, they each have a screw that must be slackened) and unscrewing the nut & bolt securing the round aerial coil from the side of the cabinet, then you can withdraw the chassis and work on the other side. This doesn't address the fact that some other capacitors (particularity one) really need replacing if they are original, but there is a very good chance it will get your set working as before. __________________ -- Graham. G3ZVT

12th Sep 2019, 6:44 pm	#23
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,222	Re: Bush DAC 90 shorting electric An aside if it is an RCD that's tripping... The incomer ('Main Switch') in my house is an RCD. A couple of times when I have had a serious overcurrent fault live-neutral (i.e. earth was _not_ involved), it tripped. Once was when a fillament light bulb failed, the other is when I did something stupid on my workbench. My guess is that there are slight inaccuracies in the differential current transformer in the RCD so that a large overcurrent in both live and neutral will generate enough signal in said transformer to trip the device. To be honest I don't really care, if I have a short across the mains or similar I want something to trip and cut the power off, I don't really mind what trips. This could explain why a DAC90 (no earth connection) with a shorted mains filter capacitor could trip an RCD.

12th Sep 2019, 11:15 pm	#25
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Bush DAC 90 shorting electric Don't use the set as other parts will fail, just sell it as it is now. It needs to be properly serviced before the power can be left on for long.

13th Sep 2019, 1:57 pm	#27
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: Bush DAC 90 shorting electric The capacitor that shorted out was a warning! All the other capacitors are of the same age and likely to do the same thing (to a greater or lesser degree). DON'T USE IT. Sell it as unrestored but working with a comment that it should be fully serviced before use. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

14th Sep 2019, 2:08 am	#28
G8UWM-MildMartin Heptode Join Date: Jan 2004 Location: Stockport, Greater Manchester, UK. Posts: 827	Re: Bush DAC 90 shorting electric If you want to continue to use it, the other posters are right: after over 70 years it really will require some further attention to work properly and avoid damage. A post in the "Repair and Restoration Services Wanted" section here would be worth a try if you don't want to do it yourself after reading the numerous threads here covering this popular model.

14th Sep 2019, 11:15 am	#29
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,088	Re: Bush DAC 90 shorting electric Definitely. This capacitor failed and fast-fried your fuses. There is another capacitor which is likely to have failed, but instead will slo-cook two of your valves, which are more expensive than fuses and moreover are a finite resource!

14th Sep 2019, 1:27 pm	#31
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Bush DAC 90 shorting electric I think we've got the message. Let's hope the OP does! __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

14th Sep 2019, 9:45 pm	#32
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,349	Re: Bush DAC 90 shorting electric The mains capacitor had failed S/C in the first DAC90 I was asked to fix. I think that capacitor was provided to filter out the hash you could get on DC mains from generator ripple and/or commutator brush sparking from DC motors. Removing the capacitor from mine had no obvious effects, and in Chelmsford it was even possible to get noise-free reception of a couple of continental medium wave stations in daytime by turning up the volume to max, whereas my state-of-the-art Sony portable with its PLL tuning and all, was completely silent. That was in the 1990's when there were still plenty of AM stations broadcasting. I did fit a replacement capacitor once I had found one before returning it.