Yes, very strange.
I suppose the transistor might have been leaky as I recall we suspected it earlier on but the transistor tester and DMM tests indicated it was working.
I have ordered five of them just in case and will install the new ones to see if that cures the problem.
I tried shorting the primary and secondary grounds directly to see if that had any effect on the rail voltage issue and it seems to remove the ~5 volt potential difference from them with no deleterious effect on the amplifier.
I'm not sure whether it is an issue to be honest, as Perry said somewhere above the RCA shields would ground out the potential difference in a car installation anyway. My only concern is that some head units have an internal fuse on their ground connection and blowing it means terrible ground noise and a a trip back to the manufacturer for repair.
I should measure the current flowing through the shorted ground and see if it significant but I want to get to the bottom of this weird bias issue first.
I attach a hopefully better resolution version of the schematic, I will try and post the PDF of the service manual too.
Edit: Service manual PDF is too big to attach, it can be downloaded for free from here: SONY XM-6020 SM Service Manual download, schematics, eeprom, repair info for electronics experts
I suppose the transistor might have been leaky as I recall we suspected it earlier on but the transistor tester and DMM tests indicated it was working.
I have ordered five of them just in case and will install the new ones to see if that cures the problem.
I tried shorting the primary and secondary grounds directly to see if that had any effect on the rail voltage issue and it seems to remove the ~5 volt potential difference from them with no deleterious effect on the amplifier.
I'm not sure whether it is an issue to be honest, as Perry said somewhere above the RCA shields would ground out the potential difference in a car installation anyway. My only concern is that some head units have an internal fuse on their ground connection and blowing it means terrible ground noise and a a trip back to the manufacturer for repair.
I should measure the current flowing through the shorted ground and see if it significant but I want to get to the bottom of this weird bias issue first.
I attach a hopefully better resolution version of the schematic, I will try and post the PDF of the service manual too.
Edit: Service manual PDF is too big to attach, it can be downloaded for free from here: SONY XM-6020 SM Service Manual download, schematics, eeprom, repair info for electronics experts
Attachments
OK, perhaps the transistor is leaky. It has succeeded to me, not only with transistors, also with MOSFET's and diodes.
Keeps us posted when new devices are inserted into the PCB.
With respect to fuses and the like, sincerely I consider that a car is not a good place to listen music with too loud volume, this can cause accidents, law problems and disturb to other conductors, so, those kind of amplifiers to be used to "boom boom" music in a car are thrash. My opinion only.
Good luck repairing it and wait for good news soon.
Keeps us posted when new devices are inserted into the PCB.
With respect to fuses and the like, sincerely I consider that a car is not a good place to listen music with too loud volume, this can cause accidents, law problems and disturb to other conductors, so, those kind of amplifiers to be used to "boom boom" music in a car are thrash. My opinion only.
Good luck repairing it and wait for good news soon.
I will certainly keep the thread updated, it will be interesting to compare the new transistor to the old in terms of measurements if it fixes the problem.
your comment about "boom boom" music and cars made me laugh, at my age my friend there is no question of annoying the neighbours and upsetting passersby...😀
I tend to listen to classical music these days and only ever crank it up very loudly when some particularly meaningful sentiment of some long dead composer compels me to. 😎😀
I play the Carmina Burana at full tilt sometimes at traffic light to scare children in boom boom cars, I confess to taking a childish joy in such things.😱😱
your comment about "boom boom" music and cars made me laugh, at my age my friend there is no question of annoying the neighbours and upsetting passersby...😀
I tend to listen to classical music these days and only ever crank it up very loudly when some particularly meaningful sentiment of some long dead composer compels me to. 😎😀
I play the Carmina Burana at full tilt sometimes at traffic light to scare children in boom boom cars, I confess to taking a childish joy in such things.😱😱
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OK. I like almost all kind of music but cumbia, regaeton and operas, because I don't understand them. I like some modern tango, classic argentine folklore, electronic music (from Mauro Picotto to Paul Oakenfold, Timo Maas, Gigi D'Agostino, Paul van Dik, John Digweed, etc), passing by The Tenors (prefer Pavarotti), Spanish singer songwritters Joan Manuel Serrat, Joaquín Sabina, Nino Bravo (RIP), Ana Belén, etc. and jazz: Monty Alexander, older jazz orquestras, etc. Summarizing, all good music.
I use mainly Electronic music from DJ's when working, or at home, but when I want to listen music and enjoy music and sing I prefer those Spanish guys.
I use mainly Electronic music from DJ's when working, or at home, but when I want to listen music and enjoy music and sing I prefer those Spanish guys.
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It turns out to have been the -15v rail Zener diode, D902, just to bring some closure on this.
I did manage to slip with a probe, in my jubilation, and have shorted a 2SA1671, can anyone suggest a modern substitute that is available from reliable sources?
I tried one from ebay but it was an obvious fake and I haven't risked installing it.
2SC5949/ 2SA2121?
I did manage to slip with a probe, in my jubilation, and have shorted a 2SA1671, can anyone suggest a modern substitute that is available from reliable sources?
I tried one from ebay but it was an obvious fake and I haven't risked installing it.
2SC5949/ 2SA2121?
The FJA4213 and FJA4313 are generally good subs for outputs. They come in the larger TO-264 case as well. The various options are given on the first page of the datasheet. These are not fully insulated so you'll need an insulator.
Thanks Perry, as it seems I can only get a minimum of five units would it be worth changing the transistors on the other channel as well?
For sonic balance or something?
For sonic balance or something?
They shouldn't sound different. The feedback circuit corrects for tiny differences in components.
They are good to have on hand as subs for various outputs.
The ones you listed may work. I recommend the FJAs because I've used a lot of them in amplifiers and never had a problem with them.
They are good to have on hand as subs for various outputs.
The ones you listed may work. I recommend the FJAs because I've used a lot of them in amplifiers and never had a problem with them.