YAMAHA HTR 5790 RUNS FOR 3 sec. then powers down?????

Yamaha model htr 5790 7.1 pro logic surround receiver regardless of input function or out put channels , produces audio for two to four seconds then powers off. Press power on with vol. all the way down then slowly bring up to -30.0 db and it stays on , any more , and it powers down.

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rodifications
Reply to
rodifications
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protection circuit genuinly or more likely falsely operating ?, check main power rails while it is operating and look for a most likely SIL IC

Reply to
N_Cook

Like ALL modern receivers this model's protection function is microprocessor based. The TA7317P and uPC1237HA protection IC's have not been used for over a decade by any major manufacturer. Dedicated protection IC's ARE NOT used except in units which do not employ microprocessors. Certainly not in Yamaha models. Nor Sony, Pioneer, Marantz, Kenwood, Denon, HK, etc etc.

The fact that the protection only activates when you raise the volume indicated either a load problem - the speaker or wire has a problem, there could be a bias problem, or there could be an open base-emitter junction on one of the affected channel's output transistors.

BTW the OP has given two different protection scenarios. One is a 3 second timeout, the other volume based. The shutdown after 3 seconds is another common problem, caused by bad low-frequency rolloff capacitors in the amplifier feedback circuit.

The HTR-5790 is a difficult unit to service. Any doit-yourself type repair attempt has a very low probability of success. Service should probably be referred to a professional.

Mark Z. Authorized Yamaha service Wichita, KS. USA

Reply to
Mark Zacharias

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Do uC based amps use the same protection criterea of power up /no AC = mute, and unbalanced/ out of range power rails? or do they add heaps more criteria?

Reply to
N_Cook

Same criteria, sometimes different implementation. For example, a TA-7317P will have one pin dedicated to monitoring a lightly filtered DC off the power supply for a fast cutoff at power-down. Many uProc versions will take a direct AC sample, perhaps squared off, for an "AC power good" signal. AS I recall, the 7317 does not monitor more than the one power supply line. A micro is not limited here. Pioneer has two PS monitor lines on recent models, and each of those may be tied to summing networks monitoring most or all DC power supplies and amp channels.

There are variances from one manufacturer to another, that's for sure. Most use a conventional "pull-up" resistor from a micro pin to the power supply. Any trigger will pull that line down. Some older Yamaha models may have a micro pin set at about 1.2 volts and positive or a negative bias from either the power supply summing network or the amp sensing network will trigger either up or down.

DC sensing resistors to the amp channels are generally around 22K for most manufacturers, but Yamaha will use different values on each channel so that in the unlikely event of equal but opposite DC offsets on different channels, the protection circuit will not be fooled.

Mark Z.

Reply to
Mark Zacharias

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So as long as you can identify the sensing routes into the micro then much the same divining process, assuming the uC or its firmware is not corrupt. Monitoring and fudging the monitored DCs until an erroneous external component is found in the amp or monitoring chain.

Reply to
N_Cook

Often it is necessary to "trick" the unit into staying on so voltages can be traced. Yamaha's of recent vintage have a "protection cancel" mode in the receiver diagnostics which accomplish this with the exception of an over-current shutdown (blown channel, shorted filter cap, etc).

I will sometimes solder a jumper across the AC contacts of the power relay and bring the unit up on a Variac to look at various voltages. The same thing can be accomplished using a POLARIZED double-ended AC cord plugged into the switched AC outlet on the rear of a receiver so equipped. Many recent models omit this feature, however, hence the solder bridge at the relay.

On many newer receivers you can power up the main board this way, completely divorced from the front panel and digital boards. The pull-up voltages will generally be missing, but you can trace the various resistors and transistor triggers etc. It is sometimes necessary to approach it this way because the summing and sensing resistors are often surface-mount devices on the underneath side of the main board, and of course no access from the bottom for service. 0.6 volts on the base of a given trigger transistor will often point you in the right direction.

The economics of such service is often debatable of course, but these days you must take what you can get, and there really isn't much competition repairing this stuff. Although there are other shops in my area nobody else around here can really do audio stuff at this level. I get stuff mailed in from surrounding states all the time. Referrals from Yamaha, Denon, Marantz, Pioneer, etc as well as a few who have seen my YouTube videos.

I generally get around 100.00 to 120.00 labor for a warranty repair of such problems. Out-of-warranty units may or may not get repaired, depends on the customer. We charge a relatively hefty diagnostic fee up-front.

Mark Z.

Reply to
Mark Zacharias

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