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

JUSTDAMO · 11th Sep 2019, 10:12 pm

Hi,

I have a bush dac 90 radio, a few months ago without warning it cut out and shorted the top half of the main electric in the house. I have changed the fuse and retried but the same thing happend.... I am guessing something component has gone but which part I don't have a clue.

I am no expert on radios just to put that out there but if its a simple part replacement I could certainly learn.

Thanks for your comments in advance

Tractionist · 11th Sep 2019, 11:05 pm

Is the radio a Bush DAC 90 or 90A? The DAC 90's commenced production in the 1940's - therefore your radio could well be seventy years old. So my question is: when was it last serviced?

These particular radios do not feature a mains isolating transformer - rather, mains power is supplied via a rear two pin proprietary plug [with no earth!] and the chassis of the set is 'live'. Any number of problems may have developed within your set, ranging from a shorted old wax/paper capacitor to a blown resistance [shorted to chassis]. One particular regular culprit tends to be the mains RF by-pass capacitor.

In any event, I would counsel that you don't even attempt to use or repair this set. It sounds to me as though it needs a through service with MANY aging and defective parts replacing. Please note that failure to follow this advice could [personal physical safety issues notwithstanding] result in further damage to the set - particularly to certain scarce and expensive components e.g. audio output valves and output transformers etc.

JUSTDAMO · 12th Sep 2019, 10:11 am

Yes its definitely dac 90 not the A version

It has a lot of dust inside so it hasnt been serviced for a while.

It did work for a few months but it happend when we had the heat wave so maybe that has something to do with it.....

kalee20 · 12th Sep 2019, 10:28 am

I do agree that it will probably need a fair bit of work to give its best performance and prevent damage to other components. However, as an AC/DC set with live chassis, there's not much that can go wrong to catastrophically blow fuses.

Almost certainly the filter capacitor, which is connected across the mains, has failed. Removing this or just snipping the leads, will prove it. The radio will work without it, you might just notice a bit more interference on weak stations.

I am not as familiar with the DAC90 as with the DAC90a so I can't say exactly which capacitor (by location in the chassis) to snip out. Hopefully someone will know immediately!

On caution - the DAC90 has asbestos lining the hot mains dropper resistor heat shield. It is possible that the fault may be that the tagboard associated with the resistor has eventually burned away (the resistor runs stinking hot) and one of the tags is now touching the chassis. If so, take appropriate precautions for dealing with the asbestos (disturb it as little as possible).

Cobaltblue · 12th Sep 2019, 10:40 am

Tractionists advice is as always excellent.

Your post suggests you had to replace the fuse on your ring main, unless I have misunderstood ?

Normal ring main is 32A so the question is why did the plug top fuse which should at most be 5A not blow ?

Does your set still have it's 2 pin plug socket arrangement on the back of the set?

Dont rule out faults in the cable if it's original.

If your going to fix this by yourself you need to start from basics and this is not the easiest or safest set to learn on.

Question is would it be better to find someone in your area to look at this?

Cheers

Mike T

JUSTDAMO · 12th Sep 2019, 11:18 am

Might be easier if I get a picture for you guys..... but it is very dusty inside :-(

It has a 5 amp fuse, in a 3 pin plug, inside are the two standard red and black wires.

The main house electrics (only on the top of the house as the radio is in the loft) trips each time I attempt to turn the radio on.

Originally when it happend the first time, I did smell a burning smell from the rear of the radio.....

I could try and take the mechanism out and submit a photo.

Well I didn't intend to keep the radio, I want to sell it on, but I would rather sell it working than non working hence if I could try and repair / replace a part then I would consider it.

ajgriff · 12th Sep 2019, 11:25 am

My advice would be to sell it unmolested as it would be more attractive to a restorer as such rather than something that has been attended to by an inexpert hand.

Alan

kalee20 · 12th Sep 2019, 11:32 am

Yes, remove the back, take a few photos, put them on here. Be aware the dust may contain a few asbestos fibres so best left as-is (it it was mine, I'd remove the dust outside on a damp day).

If you are not experienced, then don't try and remove the chassis. People have been known to break knobs trying to get them off!

JUSTDAMO · 12th Sep 2019, 12:09 pm

not sure if these are going to be much help.....

Station X · 12th Sep 2019, 12:28 pm

Can you clarify what it is that's tripping please.

If it's a Miniature Circuit Breaker (MCB) that trips this implies a short circuit in the mains plug, mains lead or the set itself.

If it's a Residual Current Device RCD that trips this implies an earth fault which is unlikely with a two wire flex, unless there's a problem in the mains plug itself.

Does the set trip the mains when switched off?

Station X · 12th Sep 2019, 12:39 pm

There's a capacitor C24 (Manufacturer's sheet) that's wired directly across the mains supply. Chances are that it's already been blown to pieces, but in either case snip it out and see if it makes a difference.

You have a meter, so you could measure the resistance between the two mains pins on the back of the chassis and report results here.

JUSTDAMO · 12th Sep 2019, 12:49 pm

Ok,

well its the first time i have switched it on for about 6 weeks. It turns out that it is is now blowing the plug fuse, rather than a main RCB/MCB circuit.....

Station X · 12th Sep 2019, 12:53 pm

It could be a fault in the lead itself. You could check this by measuring the resistance between the two sockets at the set end of the lead. Lead unplugged at both ends of course!

kalee20 · 12th Sep 2019, 12:53 pm

Helpful photos, and what I had feared about the hot resistor's tagboard is luckily unfounded!

Very likely the capacitor, as others have said. Or the lead - Station X inspiration! Just unplug the lead from the radio and see if it blows the fuse.

Station X · 12th Sep 2019, 1:08 pm

I though that the OP wouldn't want to blow another fuse, which is why I suggested a resistance check.

JUSTDAMO · 12th Sep 2019, 1:19 pm

Well it was a friends meter and I have since given it back :-(

Anyway I did plug in the lead with a new 3amp fuse which wasn't attached to the radio and it has not blown the fuse....

JUSTDAMO · 12th Sep 2019, 1:20 pm

does that mean it is the capacitor then

Station X · 12th Sep 2019, 1:20 pm

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.

JUSTDAMO · 12th Sep 2019, 1:27 pm

ok will do, might be later this evening when i do this though as my little one has just woken up

winston_1 · 12th Sep 2019, 1:31 pm

What is actually tripping? I very much doubt that a 32 amp MCB is tripping. Can we have a photo of the trip switch?

I'm having 2 thoughts here.
1. The RCD for upstairs is tripping which means there must be a path to earth. Have you got an earth plugged into the back of the radio, or perhaps an external aerial is earthed? Either way an isolation capacitor is shorted.

2. Some idiot has wired the 13 amp socket in the loft to the lighting circuit (tapped the nearest wire) and it is the upstairs lighting MCB that is tripping. Which brings us back to the filter capacitor.

11th Sep 2019, 11:05 pm	#2
Tractionist Heptode Join Date: Apr 2016 Location: Cheltenham, Gloucestershire, UK. Posts: 875	Re: Bush DAC 90 shorting electric Is the radio a Bush DAC 90 or 90A? The DAC 90's commenced production in the 1940's - therefore your radio could well be seventy years old. So my question is: when was it last serviced? These particular radios do not feature a mains isolating transformer - rather, mains power is supplied via a rear two pin proprietary plug [with no earth!] and the chassis of the set is 'live'. Any number of problems may have developed within your set, ranging from a shorted old wax/paper capacitor to a blown resistance [shorted to chassis]. One particular regular culprit tends to be the mains RF by-pass capacitor. In any event, I would counsel that you don't even attempt to use or repair this set. It sounds to me as though it needs a through service with MANY aging and defective parts replacing. Please note that failure to follow this advice could [personal physical safety issues notwithstanding] result in further damage to the set - particularly to certain scarce and expensive components e.g. audio output valves and output transformers etc. __________________ Red to red, black to black. Throw the switch and stand well back!

12th Sep 2019, 10:11 am	#3
JUSTDAMO Triode Join Date: Jul 2019 Location: Hyde, Greater Manchester, UK. Posts: 42	Re: Bush DAC 90 shorting electric Yes its definitely dac 90 not the A version It has a lot of dust inside so it hasnt been serviced for a while. It did work for a few months but it happend when we had the heat wave so maybe that has something to do with it.....

12th Sep 2019, 10:28 am	#4
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,081	Re: Bush DAC 90 shorting electric I do agree that it will probably need a fair bit of work to give its best performance and prevent damage to other components. However, as an AC/DC set with live chassis, there's not much that can go wrong to catastrophically blow fuses. Almost certainly the filter capacitor, which is connected across the mains, has failed. Removing this or just snipping the leads, will prove it. The radio will work without it, you might just notice a bit more interference on weak stations. I am not as familiar with the DAC90 as with the DAC90a so I can't say exactly which capacitor (by location in the chassis) to snip out. Hopefully someone will know immediately! On caution - the DAC90 has asbestos lining the hot mains dropper resistor heat shield. It is possible that the fault may be that the tagboard associated with the resistor has eventually burned away (the resistor runs stinking hot) and one of the tags is now touching the chassis. If so, take appropriate precautions for dealing with the asbestos (disturb it as little as possible).

12th Sep 2019, 10:40 am	#5
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,864	Re: Bush DAC 90 shorting electric Tractionists advice is as always excellent. Your post suggests you had to replace the fuse on your ring main, unless I have misunderstood ? Normal ring main is 32A so the question is why did the plug top fuse which should at most be 5A not blow ? Does your set still have it's 2 pin plug socket arrangement on the back of the set? Dont rule out faults in the cable if it's original. If your going to fix this by yourself you need to start from basics and this is not the easiest or safest set to learn on. Question is would it be better to find someone in your area to look at this? Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

12th Sep 2019, 11:18 am	#6
JUSTDAMO Triode Join Date: Jul 2019 Location: Hyde, Greater Manchester, UK. Posts: 42	Re: Bush DAC 90 shorting electric Might be easier if I get a picture for you guys..... but it is very dusty inside :-( It has a 5 amp fuse, in a 3 pin plug, inside are the two standard red and black wires. The main house electrics (only on the top of the house as the radio is in the loft) trips each time I attempt to turn the radio on. Originally when it happend the first time, I did smell a burning smell from the rear of the radio..... I could try and take the mechanism out and submit a photo. Well I didn't intend to keep the radio, I want to sell it on, but I would rather sell it working than non working hence if I could try and repair / replace a part then I would consider it.

11th Sep 2019, 10:12 pm	#1
JUSTDAMO Triode Join Date: Jul 2019 Location: Hyde, Greater Manchester, UK. Posts: 42	Bush DAC 90 shorting electric Hi, I have a bush dac 90 radio, a few months ago without warning it cut out and shorted the top half of the main electric in the house. I have changed the fuse and retried but the same thing happend.... I am guessing something component has gone but which part I don't have a clue. I am no expert on radios just to put that out there but if its a simple part replacement I could certainly learn. Thanks for your comments in advance

12th Sep 2019, 11:25 am	#7
ajgriff Nonode Join Date: May 2004 Location: Halifax, West Yorkshire, UK. Posts: 2,587	Re: Bush DAC 90 shorting electric My advice would be to sell it unmolested as it would be more attractive to a restorer as such rather than something that has been attended to by an inexpert hand. Alan

12th Sep 2019, 11:32 am	#8
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,081	Re: Bush DAC 90 shorting electric Yes, remove the back, take a few photos, put them on here. Be aware the dust may contain a few asbestos fibres so best left as-is (it it was mine, I'd remove the dust outside on a damp day). If you are not experienced, then don't try and remove the chassis. People have been known to break knobs trying to get them off!

12th Sep 2019, 12:09 pm	#9
JUSTDAMO Triode Join Date: Jul 2019 Location: Hyde, Greater Manchester, UK. Posts: 42	Re: Bush DAC 90 shorting electric not sure if these are going to be much help..... Attached Thumbnails

12th Sep 2019, 12:28 pm	#10
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Bush DAC 90 shorting electric Can you clarify what it is that's tripping please. If it's a Miniature Circuit Breaker (MCB) that trips this implies a short circuit in the mains plug, mains lead or the set itself. If it's a Residual Current Device RCD that trips this implies an earth fault which is unlikely with a two wire flex, unless there's a problem in the mains plug itself. Does the set trip the mains when switched off? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

12th Sep 2019, 12:39 pm	#11
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Bush DAC 90 shorting electric There's a capacitor C24 (Manufacturer's sheet) that's wired directly across the mains supply. Chances are that it's already been blown to pieces, but in either case snip it out and see if it makes a difference. You have a meter, so you could measure the resistance between the two mains pins on the back of the chassis and report results here. Attached Thumbnails __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

12th Sep 2019, 12:49 pm	#12
JUSTDAMO Triode Join Date: Jul 2019 Location: Hyde, Greater Manchester, UK. Posts: 42	Re: Bush DAC 90 shorting electric Ok, well its the first time i have switched it on for about 6 weeks. It turns out that it is is now blowing the plug fuse, rather than a main RCB/MCB circuit.....

12th Sep 2019, 12:53 pm	#13
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Bush DAC 90 shorting electric It could be a fault in the lead itself. You could check this by measuring the resistance between the two sockets at the set end of the lead. Lead unplugged at both ends of course! __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

12th Sep 2019, 12:53 pm	#14
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,081	Re: Bush DAC 90 shorting electric Helpful photos, and what I had feared about the hot resistor's tagboard is luckily unfounded! Very likely the capacitor, as others have said. Or the lead - Station X inspiration! Just unplug the lead from the radio and see if it blows the fuse. Last edited by kalee20; 12th Sep 2019 at 12:55 pm. Reason: Last sentence added

12th Sep 2019, 1:08 pm	#15
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Bush DAC 90 shorting electric I though that the OP wouldn't want to blow another fuse, which is why I suggested a resistance check. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

12th Sep 2019, 1:19 pm	#16
JUSTDAMO Triode Join Date: Jul 2019 Location: Hyde, Greater Manchester, UK. Posts: 42	Re: Bush DAC 90 shorting electric Well it was a friends meter and I have since given it back :-( Anyway I did plug in the lead with a new 3amp fuse which wasn't attached to the radio and it has not blown the fuse....

12th Sep 2019, 1:20 pm	#17
JUSTDAMO Triode Join Date: Jul 2019 Location: Hyde, Greater Manchester, UK. Posts: 42	Re: Bush DAC 90 shorting electric does that mean it is the capacitor then

12th Sep 2019, 1:27 pm	#19
JUSTDAMO Triode Join Date: Jul 2019 Location: Hyde, Greater Manchester, UK. Posts: 42	Re: Bush DAC 90 shorting electric ok will do, might be later this evening when i do this though as my little one has just woken up

12th Sep 2019, 1:31 pm	#20
winston_1 Hexode Join Date: Oct 2012 Location: London, UK. Posts: 498	Re: Bush DAC 90 shorting electric What is actually tripping? I very much doubt that a 32 amp MCB is tripping. Can we have a photo of the trip switch? I'm having 2 thoughts here. 1. The RCD for upstairs is tripping which means there must be a path to earth. Have you got an earth plugged into the back of the radio, or perhaps an external aerial is earthed? Either way an isolation capacitor is shorted. 2. Some idiot has wired the 13 amp socket in the loft to the lighting circuit (tapped the nearest wire) and it is the upstairs lighting MCB that is tripping. Which brings us back to the filter capacitor.