Sony STR-AV260l PCB hack repair - Page 1
Forum section: electronics / repair

author: sap chicken
author_rank: Contributor
timestamp: January 14, 2016, 04:35:02 pm
content: Hello everyone,I am in the process of modding an old radio to fit into a custom box. I used some old speakers and an old Sony STR-AV260l radio/amplifier.In order to fit it al into the box, i had to shorten the PCB. I have atached a screencap of the mod I did, with the doted line, the place I cut the PCB. The IC 501, A SIL opamp I removed.Before I did the mod, the amplifier worked fine. Now there are some problems. The display is not coming on anymore, the channel select does not work and the output relay won't switch. So there is no sound ATM.I don't think the mod was the problem becouse the only thing that got cut off were the inputs, some part of the radio I don't need, the preamplifier for the phono input and some series resistors with the input.the control board has some problems I think.Maybe I missed some improtant things that got cut off, I was wondering if any of you guy's can see something related to the mod that can cause this?My guess is that during disassembly I killed the microcontroller on the board.I checked the voltage rails, which seem fine exept for the 6.5V rail that reads 9 volts. I cannot really expain this higher voltage, it is made by a zener regulator, the voltage at the base is as it should be (arround 7V) but the voltage at the emitter is 9. It is not caused my unsuficient loading, i loaded it with 1K and still the 9V won't drop. Also the transistor is fine, replacing it did not fix it. I think it might be a output of the microcontroller doing it.Further information is thatQ803 get's warm to the touch. It is the regulator for the negative voltage (I did not check if it got warm before the mod)The green led (D302 indicated with Tape) is alway's on, which i think is coused by the 6.5V rail being 9V.analog multiplexer (IC502 TC4052BP Toshiba) input for pin 10 is also arround 9V, which should be arround 5.8 if I have to believe the schematic.I measure a frequency of 4MHz on the oscilator (x301) with my multimeter, while the schematic say's it should read about 400KHz.I can probably mod it further to remove the control board and protection just to have the amplifier, but maybe someone has some tip's to wat else could be wrong.If more information is needed, I can measure with my multimeter, solder some things and can hook up an old oscilloscope.Thanx in advanceService manual:http://elektrotanya.com/sony_str_av260l.pdf/download.html

author: Ampera
author_rank: Super Contributor
timestamp: January 18, 2016, 03:30:26 am
content: Just looking at it makes me wonder if any other traces were cut, but if you say that only the inputs were gone, I believe you.The old Sinclar ZX Spectrum was a botch job in it's own right. The tape loading went straight through the audio system, so you would hear the contents of the tape.It could be possible that by leaving inputs hanging or excluding a possible component that might have been in the inputs you cause the power to go higher, either stalling orfrying something. The reason I bring up the Spectrum is that things were wired strangely, like important stuff would go where you wouldn't even imagine.If you want a suggestion try reattaching everything and see if it works. First rule of making a modification. If it worked before you changed it, and now it doesn't undo as best you can what you did. Not saying glue the board back together, but see if you can reattach the inputs and whatever traces you might have cut. Just an idea, but it could stillbe possible they did something hidden and weird that relies on the Inputs.Other then that, no clue.

author: sap chicken
author_rank: Contributor
timestamp: January 19, 2016, 03:49:55 pm
content: Thanx for the replyI think I have spend at least a few hours on debugging the thing.Fixing the circuit to it's original state did not help much. I gave up on the digital part and just modded it some more to test only the amplifier. It did not work either.It had a weird -9.5 DC output...I found a BIG problem with my mod, and it had nothing to do with the cutting of the PCB. I started folowing the ground planes of the PCB and they don't connect at some points. I think the radio uses the metal housing as conductor for the ground. I made a new housing out of MDF so, no conduction and thus wird voltages everywhere. Did not expect the verry creative ground plane.I will try and fix that to see if it fixes the amplifier. Then I might try and reconnect the display.Do you know if this is a common method of connecting the ground in a circuit? I think it is quite a weird solution, never saw that used anywhere.

author: macboy
author_rank: Super Contributor
timestamp: January 21, 2016, 02:54:00 pm
content: Yes, many Sony amps (and other brands I suspect) use the chassis as a common ground point for some parts of the circuit. You will need to find those orphaned grounds and reconnect them with wire. Connect from the intended ground connection (usually a screw hole) back to the point between the two large power capacitors... you can clearly see a "star" ground at that location on the PCB.

author: sap chicken
author_rank: Contributor
timestamp: January 22, 2016, 12:04:09 pm
content: It's working now, great sound. Found it funny that they have this nice star ground and then daisy chain the rest of the circuit ground via very thin traces to screw terminals to the chassis. Anyway, they did a good job, thing must be like 30 years old, left it for like 10 years in a cabin outside and still doing great with good sound.