Greetings all, I picked up a JVC RX-709X Digital Surround System Receiver, the guy said that one of outs might be shorted, all it dose is sit there and click the relay over and over again with a spark each time it dose. It did turn on once but shut off quickly.
Is that the likely problem and is the unit worth fixing.
Also any leads on the parts they say "Toshiba 2sb1429" Toshiba "2sd2155" for the left channel, the right I can't read.
Is that the likely problem and is the unit worth fixing.
Also any leads on the parts they say "Toshiba 2sb1429" Toshiba "2sd2155" for the left channel, the right I can't read.
Hi gto127,
It is entirely possible that your new outputs are now dead. You have to test the drivers and previous transistors as well. A great rule of thumb I have taught for years is to replace components one stage further back from the last blown part. Transistors mostly, but do check the resistors. After this type of damage, the differential pair is often damaged (but still kinda working) and should be replaced with a matched pair. This will generally get you running again. You will have to set the bias currents, or at least check them. If there is a DC offset adjustment, that might need correction.
Finally, don't forget the speaker protection relay. It's contacts are burned, so once you get the amp fixed, order a new relay and fit it.
I'm sorry, but I am not surprised that the receiver is still in protection mode. A power amplifier is never repaired by replacing just the outputs, it may run but it isn't good as new by any stretch of the imagination.
-Chris
It is entirely possible that your new outputs are now dead. You have to test the drivers and previous transistors as well. A great rule of thumb I have taught for years is to replace components one stage further back from the last blown part. Transistors mostly, but do check the resistors. After this type of damage, the differential pair is often damaged (but still kinda working) and should be replaced with a matched pair. This will generally get you running again. You will have to set the bias currents, or at least check them. If there is a DC offset adjustment, that might need correction.
Finally, don't forget the speaker protection relay. It's contacts are burned, so once you get the amp fixed, order a new relay and fit it.
I'm sorry, but I am not surprised that the receiver is still in protection mode. A power amplifier is never repaired by replacing just the outputs, it may run but it isn't good as new by any stretch of the imagination.
-Chris
Hello Chris, It didn't blow the outputs again. I checked output stage & everything seems fine. The relay that's clicking is the main power on relay-not the speaker relay. I did trace voltage coming from main board which cuts on power relay and that is cutting on & off continously. It appears to be coming from CPU board(this one has plug in cards). That's as far as I got with it so far.
Hi gto127,
Cool, I'm glad to hear this.
Look for a diode feeding a 1 uF capacitor (or similar) that detects AC power good. They often go bad and can cause this exact problem. This is normally located in the power supply area. Looking at lower value capacitors with a scope will probably show one with extreme ripple to pulsating DC.
-Chris
Cool, I'm glad to hear this.
Look for a diode feeding a 1 uF capacitor (or similar) that detects AC power good. They often go bad and can cause this exact problem. This is normally located in the power supply area. Looking at lower value capacitors with a scope will probably show one with extreme ripple to pulsating DC.
-Chris
Hi gto127,
It's typically the capacitor. The cap is expected to discharge quickly if the power fails (like being turned off for example) and signalling the CPU to mute and shut down. A shorted diode would kill the capacitor and hopefully blow a fuse somewhere. But the load is light and you may even see a 1/2 ampere diode used, or even lighter. The capacitance is going to be close to 1 uF. Just look for a little diode and small capacitor grouped together near the rectifiers or regulators.
These days you can pick up a 100 MHz dual trace working 'scope for less than $100 USD, less than $200 for a Tek 465 or 2235. That's pretty incredible, considering what they were worth. Every time I had to buy a scope for my shop, the 100 MHz dual trace with cursors cost me over $2K each. Closer to $2500 for a Leader or similar.
For a DSO, the Rigol scopes seem to be pretty darned good, and less than $1K (lower frequency). But I would recommend you get an analog scope first and keep it along with a DSO. That is exactly what I am doing. The analog scopes were very robust compared to the digital "toys" out there today.
You can't afford to have a flaky scope on your bench in terms of wasted time and mistakes. Good luck with yours. Can you borrow one mean time?
-Chris
It's typically the capacitor. The cap is expected to discharge quickly if the power fails (like being turned off for example) and signalling the CPU to mute and shut down. A shorted diode would kill the capacitor and hopefully blow a fuse somewhere. But the load is light and you may even see a 1/2 ampere diode used, or even lighter. The capacitance is going to be close to 1 uF. Just look for a little diode and small capacitor grouped together near the rectifiers or regulators.
I use my scope almost all the time for rough voltages or ripple checking. You really want to see if you can fix your scope (or replace it) soon as it is the second most important instrument you have. A good analog 5 ~ 20 MHz dual trace is the most useful type to have. DSOs tend to be fragile, and the USB variety is even more so. Mine died, but not before I found that it was best used for repetitive setups on signal voltages. With a X10 probe, your maximum input voltage is 50 VDC. Not per division, 50 V peak - period. You can (and will) exceed this without even thinking about it.
These days you can pick up a 100 MHz dual trace working 'scope for less than $100 USD, less than $200 for a Tek 465 or 2235. That's pretty incredible, considering what they were worth. Every time I had to buy a scope for my shop, the 100 MHz dual trace with cursors cost me over $2K each. Closer to $2500 for a Leader or similar.
For a DSO, the Rigol scopes seem to be pretty darned good, and less than $1K (lower frequency). But I would recommend you get an analog scope first and keep it along with a DSO. That is exactly what I am doing. The analog scopes were very robust compared to the digital "toys" out there today.
You can't afford to have a flaky scope on your bench in terms of wasted time and mistakes. Good luck with yours. Can you borrow one mean time?
-Chris
I had temporarily fixed my scope a few months back by spaying contact points with de ox it. Seems it's back about like it was now so maybe needs a deeper cleaning or maybe other issue. Mine is Hitachi quad trace 100mhs although I only have 1 lead as I purchased used awhile back. I never was a TV tech so I know very little about the circuitry. I don't know anyone with a working scope.
Hi gto127,
Okay, pretty good 'scope then. Try cleaning those switches with a non-residual cleaning spray (although I hate sprays). Do not get any into trimmer capacitors and try to avoid components by blocking over spray with cards. Watch for liquid dripping too. Don't follow with anything else. Just the non-residue cleaner.
Try to avoid lubricated parts of the switches as well. Use as little as possible to accomplish the cleaning you need.
-Chris
Okay, pretty good 'scope then. Try cleaning those switches with a non-residual cleaning spray (although I hate sprays). Do not get any into trimmer capacitors and try to avoid components by blocking over spray with cards. Watch for liquid dripping too. Don't follow with anything else. Just the non-residue cleaner.
Try to avoid lubricated parts of the switches as well. Use as little as possible to accomplish the cleaning you need.
-Chris
Got back on amp with no progress. Checked it over & no 1uf caps in supply areas. 47uf at standby relay rectifiers and various values from 2.2 on up around large transformer rectifiers. I did find a similar schematic rx-717 at least in power supply areas appears to be same. JVC RX-717V Manual - Audio Video Control Receiver - HiFi Engine
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