Hello valve amp users.
Hope someone has some advice.
Unison Research Smart 845 monoblocks appear to be suffering from melted wire insulation to the extent that sticky goo has dripped out through bottom cover vents.
Had a look and it appears that the wire insulation is melting or breaking down.
One mono has failed completely .. shorting out? .. it blows the fuse holder fuse when turned on. The other still works OK but as dripping has started I assume that it’s days are limited before it ‘packs up’.
I’m no electronics expert .. but from a visual inspection and fact that fuse blows .. I suspect that either wiring short due to insulation literally melting away or component failure. But as both mono’s have same melting wire insulation problem I doubt that component failure is the cause. A further pointer to the wiring is that my Mystery 1 pre amp has no sign of such a problem and was bought at same time as mono’s so I’ll wager that it has the same sort of wiring with less load going through it .. but like I say .. I’m no expert.
Age of amps is 15 - 16 years
Cost of dealer / importer repair is too high to even consider .. so my as well try my hand at fixing it .. although I can enlist the help of an 81 year old who knows more than me about electronics.
Not a rush job as I’ve got a spare integrated amp to use but don’t really want it to become ‘long term’
Searched site and found old thread that really didn’t go anywhere with the problem.
Will stop boring you all further
david
Hope someone has some advice.
Unison Research Smart 845 monoblocks appear to be suffering from melted wire insulation to the extent that sticky goo has dripped out through bottom cover vents.
Had a look and it appears that the wire insulation is melting or breaking down.
One mono has failed completely .. shorting out? .. it blows the fuse holder fuse when turned on. The other still works OK but as dripping has started I assume that it’s days are limited before it ‘packs up’.
I’m no electronics expert .. but from a visual inspection and fact that fuse blows .. I suspect that either wiring short due to insulation literally melting away or component failure. But as both mono’s have same melting wire insulation problem I doubt that component failure is the cause. A further pointer to the wiring is that my Mystery 1 pre amp has no sign of such a problem and was bought at same time as mono’s so I’ll wager that it has the same sort of wiring with less load going through it .. but like I say .. I’m no expert.
Age of amps is 15 - 16 years
Cost of dealer / importer repair is too high to even consider .. so my as well try my hand at fixing it .. although I can enlist the help of an 81 year old who knows more than me about electronics.
Not a rush job as I’ve got a spare integrated amp to use but don’t really want it to become ‘long term’
Searched site and found old thread that really didn’t go anywhere with the problem.
Will stop boring you all further
david
Power transformer, yes?
If so, then you have a bad filter cap in all likelihood.
Output xfmr, a bit more tricky.
Let's start with this...
Also how hot did the can of the xfmr get, or did you not notice??
Is the goo black?
Which would be tar.
_-_-
PS. the preamp or other gear has nothing to do with it.
Where are you located?
If so, then you have a bad filter cap in all likelihood.
Output xfmr, a bit more tricky.
Let's start with this...
Also how hot did the can of the xfmr get, or did you not notice??
Is the goo black?
Which would be tar.
_-_-
PS. the preamp or other gear has nothing to do with it.
Where are you located?
Dripping goo Unison 845 etc
Hi David,
This is NOT a problem. It is actually the varnishy insulation on some of the wiring that has degenerated due to time.
It can be cleaned off with petrol (preferably) or safely with IPA.
The fuse blowing is a different matter, but I do not think it is the transformer, more likely to be the heater bridge rectifier.
Please pm me with email address/phone nr. and I will help sort out over the phone/email if possible, or you can bring it to me
John - UKD -Unison importer service engineer
Hi David,
This is NOT a problem. It is actually the varnishy insulation on some of the wiring that has degenerated due to time.
It can be cleaned off with petrol (preferably) or safely with IPA.
The fuse blowing is a different matter, but I do not think it is the transformer, more likely to be the heater bridge rectifier.
Please pm me with email address/phone nr. and I will help sort out over the phone/email if possible, or you can bring it to me
John - UKD -Unison importer service engineer
Hello All
Thanks for responses.
Slight delay replying as my posts have to be OK’d by site admin. as I’m a new member.
Didn’t expect such fast replies.
I’ve got a Teac T1 in bits at the moment .. common 2 step gear failure .. so bench is full.
Just my luck for 2 things to go wrong at same time!!
Matt - Will post some photos of both dead and working monos in a couple of days ...
Thanks for warning .. I now leave anything unplugged for a couple of days .. I wasn’t aware of that fact 20 years ago and I found out the hard way! .. it hurts!
SY - Ditto above for photos
Bear - All I can say is that it was not all black goo .. had some reddish colour mixed in.
Never noticed any overheating or smelt anything ..worked OK when last used until next turning on then nothing. No pops or bangs .. just didn’t work .. obviously due to blown fuse.
Unfortunately, I’m not an electronics person so don’t really understand about caps & outputs etc.
John - Many thanks for the offer. Will get back to you when I’ve got T1 out of the way.
I'm not into naming names .. but I can only assume that dealers I contacted were more interested in selling a replacement than getting 15 -16 year old amp fixed .. horror stories of hundreds of pounds to find out what was wrong which could lead to 4 figure repair costs. Hence my comment about importer repair not been an option!
Unfortunately owner of dealership / shop that supplied the Mystery & Smarts .. Zen Audio @ Hull sold business many years ago.
I'm in West Yorkshire and assume that you are many miles South of me so would have to be delivered .. but I still have original box's.
david
Thanks for responses.
Slight delay replying as my posts have to be OK’d by site admin. as I’m a new member.
Didn’t expect such fast replies.
I’ve got a Teac T1 in bits at the moment .. common 2 step gear failure .. so bench is full.
Just my luck for 2 things to go wrong at same time!!
Matt - Will post some photos of both dead and working monos in a couple of days ...
Thanks for warning .. I now leave anything unplugged for a couple of days .. I wasn’t aware of that fact 20 years ago and I found out the hard way! .. it hurts!
SY - Ditto above for photos
Bear - All I can say is that it was not all black goo .. had some reddish colour mixed in.
Never noticed any overheating or smelt anything ..worked OK when last used until next turning on then nothing. No pops or bangs .. just didn’t work .. obviously due to blown fuse.
Unfortunately, I’m not an electronics person so don’t really understand about caps & outputs etc.
John - Many thanks for the offer. Will get back to you when I’ve got T1 out of the way.
I'm not into naming names .. but I can only assume that dealers I contacted were more interested in selling a replacement than getting 15 -16 year old amp fixed .. horror stories of hundreds of pounds to find out what was wrong which could lead to 4 figure repair costs. Hence my comment about importer repair not been an option!
Unfortunately owner of dealership / shop that supplied the Mystery & Smarts .. Zen Audio @ Hull sold business many years ago.
I'm in West Yorkshire and assume that you are many miles South of me so would have to be delivered .. but I still have original box's.
david
it is incorrect that leaving the amp "unplugged" assures that there are no dangerous voltages lurking.
the only proper way to do this is to actually test with a voltmeter, DC voltmeter. with the amp unplugged.
you would probe between ground and all the high voltage points. insulated clip leads and bleeder resistors should be used to drop any residual voltages.
consumer equipment that was properly designed would have bleeder resistors, and assuming that the bleeders are not open or other wise damaged, then the voltage should self bleed down. testing assures that the bleeders did their job(s). Typically a few minutes is all that is required to bleed down at most.
_-_-
the only proper way to do this is to actually test with a voltmeter, DC voltmeter. with the amp unplugged.
you would probe between ground and all the high voltage points. insulated clip leads and bleeder resistors should be used to drop any residual voltages.
consumer equipment that was properly designed would have bleeder resistors, and assuming that the bleeders are not open or other wise damaged, then the voltage should self bleed down. testing assures that the bleeders did their job(s). Typically a few minutes is all that is required to bleed down at most.
_-_-
Dripping goo Unison 845 etc
Hi David,
Of course I am miles away from you that is sods law
However I am pretty sure it can be fixed remotely if you can find someone relatively competent nearby. As far as leaving the amps to discharge, as you say you are not competent please leave well alone, these amps run at 1000V on the 845 valves and will give you a nasty surprise, and some of them did not have bleed resistors fitted to the HT caps
Bear, no the goo is definitely off of the wiring. Depending on the age there will be red green and black - it is not dangerous but it is messy and very sticky.
John etc
Hi David,
Of course I am miles away from you that is sods law
However I am pretty sure it can be fixed remotely if you can find someone relatively competent nearby. As far as leaving the amps to discharge, as you say you are not competent please leave well alone, these amps run at 1000V on the 845 valves and will give you a nasty surprise, and some of them did not have bleed resistors fitted to the HT caps
Bear, no the goo is definitely off of the wiring. Depending on the age there will be red green and black - it is not dangerous but it is messy and very sticky.
John etc
Bear, I agree completely!
I only said that as I was not aware David knew the dangers. Even then it's obvious to test first but I guessed he didn't have any kit to test with. So time was the key.
David, I am in Cheltenham and would be more than happy to take a look for you. I have built a GM70 amp with 6e5p driver and Mosfet follower for A2, so you can be assured I can work around such an amp.
Cheers
Matt.
Edit, just saw that you are in Yorkshire. My wife is from Skipton and we visit regularly. PM me if you would like me to take a look. I can bring some kit up so no Probs there.
I only said that as I was not aware David knew the dangers. Even then it's obvious to test first but I guessed he didn't have any kit to test with. So time was the key.
David, I am in Cheltenham and would be more than happy to take a look for you. I have built a GM70 amp with 6e5p driver and Mosfet follower for A2, so you can be assured I can work around such an amp.
Cheers
Matt.
Edit, just saw that you are in Yorkshire. My wife is from Skipton and we visit regularly. PM me if you would like me to take a look. I can bring some kit up so no Probs there.
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The one with blowing fuses may need the transformer rewound hence the high estimate for repair. It is likely that either the main smoothing capacitor has failed to a short circuit or the grid coupling capacitors have gone leaky making the output tubes run hot and draw too much currant from the power supply. This will make both transformers get hot. I would expect the resin or tar to have come out of an overheating transformer. I have a home made coil winder in my workshop and also I live a little closer.
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Dripping goo Unison 845 etc
Hi all,
There is a little too much OTT speculation here. As I said earlier I doubt it is transformer failure, more likely rectifier failure.
The goo is wire insulation not transformer pitch as the transformers are vacuum VARNISH impregnated.
I feel we need to wait to get someone that can look at it before we jump to erroneous conclusions.
John UKD service engineer
Hi all,
There is a little too much OTT speculation here. As I said earlier I doubt it is transformer failure, more likely rectifier failure.
The goo is wire insulation not transformer pitch as the transformers are vacuum VARNISH impregnated.
I feel we need to wait to get someone that can look at it before we jump to erroneous conclusions.
John UKD service engineer
Many thanks to all who have responded to my initial post.
Your advice and comments much appreciated.
Indeed, I surprised by the variety of replies received; as my Teac T1 post has received none to date! Fortunately much trial & error has sorted problem .. took some time though.
I agree with John’s comment regarding speculation; until some detailed facts are available; which hopefully I can provide.
Working away for a week from tomorrow so will have to put on hold until I return. Don’t have iphone or tablet gadgets.
Finished T1 tonight so bench should be cleared tomorrow .. finally .. then full speed ahead with 845 mono .. hopefully.
Just an observation .. I’m presently using a 200W @ 8 ohm integrated amp which doesn’t seem to have 8 times the power of the 845’s. So much for specs. Will be interesting to do a comparison .. if I get the 845 fixed!
david
Your advice and comments much appreciated.
Indeed, I surprised by the variety of replies received; as my Teac T1 post has received none to date! Fortunately much trial & error has sorted problem .. took some time though.
I agree with John’s comment regarding speculation; until some detailed facts are available; which hopefully I can provide.
Working away for a week from tomorrow so will have to put on hold until I return. Don’t have iphone or tablet gadgets.
Finished T1 tonight so bench should be cleared tomorrow .. finally .. then full speed ahead with 845 mono .. hopefully.
Just an observation .. I’m presently using a 200W @ 8 ohm integrated amp which doesn’t seem to have 8 times the power of the 845’s. So much for specs. Will be interesting to do a comparison .. if I get the 845 fixed!
david
No worries David, you will get it fixed😊 I'm sure it will be something simple. Trouble is along the way you will see other things you will like to tweak. After that the bug has well and truely bitten.
Sorry for the odd double posts, don't know what was going on there. Back button maybe?
Cheers
Matt.
Sorry for the odd double posts, don't know what was going on there. Back button maybe?
Cheers
Matt.
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