Yamaha rev7 oddidty

[pucho812]

This is a good one.  We have a rev7 at the studio and first power up of the day, the unit will run about 4 hours before  it stops with the reverb and just passes dry signal. When the unit stops reverb, the screen  will show the yamaha logo, initial start up logo,  and stay there while the background  of the lcd screen flickers. I pulled the unit apart and found a bad BP lytic cap and a leaking cap in the PSU.  I see +/-15VDC and 5VDC as I should from the power supply but over time the 5V line will start to drop when under load, slowly but surely until it's below minimum operating voltage of the things. I have brought it back buy adjusting the trim pot, but this is a temp fix as the unit will start to drop the 5V down under load right away.
Has anyone seen this before? I am certain it's a power supply issue and or something is going into thermal shutdown.

 

[Rob Flinn]

These PSU's are notorious for doing this sort of thing.  Normally recapping them sorts the problem.  I have had ones where a diode or resistor has had a leg broken/corroded too, but I could see that so it was reletively easy to find.    Anyway it costs next to nothing to recap so I would try that first.

 

[Tubetec]

I havent worked on a REV7, but I have fixed an Spx-90 and other similar Yamaha units . There could be a back up battery in there too that might need a check .If the battery is in poor condition it can lead to the thing not booting up properly.
I definately second Robs advice  , leakage of the caps needs to be cleaned up ,and its fairly corrosive stuff that can eat tracks and component legs or cause leakage currents that can drag voltages down on the regulators. The good news is once you clear these faults you'll have a usable and reliable unit again , the sound is a wee bit crusty by modern standards ,it is 35 years old after all . Thing is on certain sources the lo-fi crunge adds something you wont get on a modern 24 bit unit. The Spx1000 multifx is another unit that has plenty of charachter so might be worth picking up on the cheap if you find it ,  that unit was all over 'Achtung Baby' by U2, for me one of their best albums.

 

[pucho812]

Yes recap. I started in on that. When testing I only found 1 bad cap in the psu but the values are relatively inexpensive so can easily do the rest.  What’s odd is works fine for hours and then goes wonky. My guess would be thermal but nothing is to hot to touch.
Battery was also replaced the other day

 

[Tubetec]

Ive sometimes come across solder joints that look good to the eye yet are intermittant ,especially in close to rectifier bridges and regulators , in some cases  found it worthwhile to reflow the solder just as a matter of course on everything in the vicinity of the psu . Thermal fatigue I agree seems to be a likely culprit , racks can end up running at elevated temps ,cyclic heating and cooling eventually metal fatigue takes its toll. A lot of these type of faults you also see with keyboards/synths of the same vintage which have similar Japanese made electronics and components. Freeze spray might help reveal something.

 

[cyrano]

A typical Yamaha problem, I'm afraid.

I've completely re-soldered my dad's CR800 receiver five times in the 30+ years he's had it. In the same period, I've replaced one capacitor (DUAL 721 turntable) and repaired one tweeter (Celestion Ditton 66 speakers) in the rest of the chain. Oh, and six Shure V15III or V15IV elements.

The first time it was easy, as I could see sparks flying from the bad joint. After that, it became exponentially worse 'till I ended up doing every single one of them.

 

[cyrano]

I'm clumsier every day...  :

Succeeded in quoting my own post, so mods, please delete this one. Sorry.

 

[pucho812]

I'm clumsier every day...  :

Succeeded in quoting my own post, so mods, please delete this one. Sorry.

o.k. I'm not the only one

 

[pucho812]

Well ha-Za, ha-za... went over the psu tonight. Put in the last of the caps tonight in the psu. Found a completely oxidized solder joint that was on an inductor in the 5v line. The moment I cleaned it all off down to the solder pad and reflowed the solder, I was able to test and have a solid 5vdc, no more jumping around. Time to test run it for a long period and see what it do.