Hi All,
First post. Hope everyone is well. I am about to start repairing my dads Leak 70 amplifier however he also had my late Uncles Stereo 70 which 'didn't work' - I got this first as a trial run to get familiar with the insides and the schematics, with no risk of any further damage to my dads when Is I start on it. My uncles one was deemed to be gubbed beyond repair, however I noticed very quickly there was no DC voltage getting to it, then noticed that there was no way it could since there was a small bracket thing mounted on the transformer body (3 pin) with a leg going to the transformer and the other leg going to the diodes. There was no connection between the two, so basically it would never work. This was not reflected on the schematic I had or most pictures I could find of the transformer which showed no such 'interruption' to the circuit.
I eventually found an image showing this part and an alternative schematic also showing it, a green part that looked a bit like a high wattage resistor but I assumed it was a thermal fuse. The transformer in my uncles amp had clearly been replaced (also had a date code sticker of the year of his passing) so I think that someone has replaced the transformer but not fitted the part in question. I linked the two pins and hey presto, amp working well and sounding great.
So the question is, what is this part ? Is it a thermal fuse ? If so was this just a bodge to get around UL standards that came out stating transformers had to have one (I think for northern US and Canada), the schematic I have which includes it perhaps refers to it as a Temperature compensation diode? If it is a Thermal fuse, I fail to see how it could ever get hot enough to pop given it is not in contact with the transformer windings (I believe the common way of incorporating these is in the windings. Picture of the missing part attached (the green part).
Many thanks!
First post. Hope everyone is well. I am about to start repairing my dads Leak 70 amplifier however he also had my late Uncles Stereo 70 which 'didn't work' - I got this first as a trial run to get familiar with the insides and the schematics, with no risk of any further damage to my dads when Is I start on it. My uncles one was deemed to be gubbed beyond repair, however I noticed very quickly there was no DC voltage getting to it, then noticed that there was no way it could since there was a small bracket thing mounted on the transformer body (3 pin) with a leg going to the transformer and the other leg going to the diodes. There was no connection between the two, so basically it would never work. This was not reflected on the schematic I had or most pictures I could find of the transformer which showed no such 'interruption' to the circuit.
I eventually found an image showing this part and an alternative schematic also showing it, a green part that looked a bit like a high wattage resistor but I assumed it was a thermal fuse. The transformer in my uncles amp had clearly been replaced (also had a date code sticker of the year of his passing) so I think that someone has replaced the transformer but not fitted the part in question. I linked the two pins and hey presto, amp working well and sounding great.
So the question is, what is this part ? Is it a thermal fuse ? If so was this just a bodge to get around UL standards that came out stating transformers had to have one (I think for northern US and Canada), the schematic I have which includes it perhaps refers to it as a Temperature compensation diode? If it is a Thermal fuse, I fail to see how it could ever get hot enough to pop given it is not in contact with the transformer windings (I believe the common way of incorporating these is in the windings. Picture of the missing part attached (the green part).
Many thanks!
Hi ,for me it looks like resistor , maybe 1w or so. Resistors sometimes used as fuses ,there are special ones ,who break like normal fuse and don't smoke. Try to desolder it and take a picture of printings on it. I see its goes related to diode bridge , maybe one of diodes shorted and fuse blowed.
Thanks, that isnt a picture of my amp, I dont have the part in question - that is a picture of one online that has the part. I just have the 3 pin board and I have put a wire link in place of the part which is missing. There is already a fuse on the DC output, so I dont think it is just a fuse as such.
Its the part in yellow on the diagram below, it has a fuse symbol and a fuse reference (T4 / T5 indicating 4 or 5A) but I cant grasp why they would have added a 2nd fuse like that ? Even if it just to have a faster blowing fuse say, then why not just change the one in the fuse holder that is already there, to a faster blowing type? Unless the thinking is that maybe someone would replace the external fuse with the wrong type and risk the amplifier, hence by putting an internal fuse there they safeguard against such a user error ?
In properly designed devices ,there are multiple levels of fusing. Mains ac fuse , secondary winding has its own fuse , in case diode bridge shorts ,to prevent overload of transformer, until mains fuse blows. Also dc output after bridge may have its own fuses for each channel, to ensure unit still can operate ,when one channel is inoperative ,damaged .
Regarding yellow fuse in schematic , i still think this can be resistor in place of it , to reduce turn-on current when capacitors are discharged, also there are many different types of fuses ,also ones ,looking like resistors.
Regarding yellow fuse in schematic , i still think this can be resistor in place of it , to reduce turn-on current when capacitors are discharged, also there are many different types of fuses ,also ones ,looking like resistors.
Yes true. Thanks. I think if it was a resistor it would show a resistor value on the diagram though, its definitely a fuse symbol, I might just fit a fast blow leaded fuse in there at the rating indicated. The red numbers relate to the Leak 70, black to the 30
If you wanna be sure about transformer protection, add that missing fuse ,ir may be in other dimension form ,like 5x20mm , add holder to fuse ,so it may be replaced if needed. Also you can upgrade diode bridge, to ensure it will be more powerful and not fail during turn on . Old diodes had higher voltage drop and less current than modern ones . From photo it's not clear if there are 1n400x or 540x diodes.
As the amp appears to work properly with the missing part shorted, there's no need to touch the diodes, as they're apparently ok. Just replace the missing part by a 5x20 mm 5 A slo-blo fuse plus holder, as yet proposed.
Best regards!
Best regards!
This is a fuse, once I had a machine like this, it didn't work, an internal fuse blew, T-head, fast fuse, just change it, in fact, this is a fuse designed to prevent damage to the rectifier bridge, very good design, I hope it helps you,🙂
Yes, this machine can be polished and polished. In fact, it can be equipped with a relay to eliminate the impact sound on the unit when starting up,
This (the NTC) is not confirmed by the schematics excerpt in #4. It's a fuse, obviously.
Best regards!
Best regards!