Hitachi SR-604, where to start

I did build the DBT. My logic for replacement of the fusible resistors first (before DBT) was based on the fact that the DBT is a tool to safely power on the unit and do some diagnosis without fear of ruining anything. I figure testing these resistors with no power was the safest diagnostic step I could take - and definitely showed some defective components. Ultimately, the DBT seems to me to be a device that one way to find defective pieces - so didn't think powering up with DBT to then verify that something was wrong and then learning that the resistors are bad seemed redundant.

Given that my replacement parts arrive on Thursday, I'll quickly put them in and then use the DBT.
 
Working in between family (adult parent) challenges. All I can say is Alzheimer's sucks - and I hope I don't become afflicted with it.

Anyway, received the parts and have installed them into the Audio Board (2). That's since been installed in the main board, the bottom re-attached - so the only part not back on is the cover. I'll leave that off when I plug into the DBT and fire it up (hope fire isn't the operative word!).

Question for the forum. Should I have a load attached to the speaker ports? Or, should I leave volume at low with no speakers attached - and see what happens first?

Thanks!
 
Ok, I'm making progress. Today I hooked up the SR-604 to the DBT and powered it up. Light flashed briefly and then went to light orange glow - which I assume means ok - at least not a dead short. I then heard my relay kick in - panicked - and turned off the receiver. That was dumb. So, I powered it back on - and waited for my relay to kick in and it didn't. After a minute or so I switched off the receiver. I waited a minute or so and switched it back on - after about 10 seconds - the relay clicked. The DBT didn't flinch, so I figured I was in good shape.

I observed things for a while, noting temps using the IR temp feature of my multi-meter. After a while, I could smell things getting warm, but not hot. I checked the transistors connected to the heat sink. I noted the following temps: Q714L = 75, Q715L = 75, R714R = 78, Q715R = 106. Also, Q801 was measured at 82. All readings are in Fahrenheit - and the house was at 67 degrees - which all components initially read at power on. I'm assuming all of these readings are fine (BTW, volume was at zero and speaker a and speaker b were switched off - no speakers attached).

I did note that R802 was at 90 degrees and R801 at 116, also in Fahrenheit. So, I'm thinking nothing is getting really hot.

I then measured idle voltage and current. TPL L showed 33.1 mV and 13.26 mA, TPL R showed 28.0 mv and 11.61 mA. Service manual showed spec as 8.8mv +- 4.4mv and 40mA +- 20 mA. So, these look to be out of spec. Is it enough to cause the relay to not click?

Finally, I checked voltages at Q708L - because it was fairly easy to access. If I read the SM correctly, the voltages for C/B/E should be 48/19.2/? respectively. I measured C=29.11 and B=10.82. So, assuming I've read the manual correctly, I think the voltages coming in too low. Hopefully that gives the forum so good info.

I'll now stand by waiting to hear from you experts on my next test/measurements!
 
glad you're back at it.. I would attempt to get the idle in spec. I'd shoot for 8 mv. the adjustments don't need to be super exact just be sure you don't turn the pot's clock wise as that is plus mv and you'll probably blow a driver transistor. Putting caution on the idle pots, they can be sensitive and most are not meant to be continually adjusted and the slightest turn can result in a few mv on the meter. In other words lets see if you can adjust the idle or if not then you have another issue.

give it a warm up period of about 5 minutes and you'll have to recheck your adjustment.. you may see drift upwards if not fully warmed up and I saw no time period but a lower mv target is better than too high.
 
Hope you figure yours out, I have been working on a sr-903 for a while now.... Would love to hear that relay click!!
 
Ok, today I got back to it. Got my meter attached to the two left test points and powered it up. As before, no relay click. As Binkman nicely recommended, I adjusted counter-clockwise (it was near 23 mv to start) and brought it down to just over 8 mv. AND - I believe I heard the relay click!!!

I then disconnected my meter (using my new meter clips as recommended in the sticky thread on recommended tools) and moved over to the right side. As soon as I connected my leads I heard/saw a small spark - and my meter registered just 1mv :(. Should I have powered down the receiver prior to connecting the leads?

Anyway, I've not tried to adjust the right side to a higher value.

What are my next steps folks? Did I blow something? I'm feeling bad...please make me feel better!!!
 
give it another try on the other side.. if you have no adjustment then you know if something went. You have to be very very careful not to short leads. but you may be okay.
 
I gave it another try - and not able to adjust the right side. So, I powered down and decided to do a bit of detective work. I started with the fusistors that I just replaced - and YES the 47 ohm resistor was showing 1.5M ohms - not good. Checking the left side showed it right at 47. I checked the remainder of the fuse resistors and they all looked good. So, I replaced the one bad one, connected the multimeter prior to power up. Looked better on the meter as it showed an output - and my relay clicked!! Yes!! I then adjusted both sides after allowing time for warmup. It's interesting, but a quick power down to move the leads and power back up - still took a minute or so to stabilize. But, the relay is now clicking every time.

I don't have anything connected to the speakers yet - and don't have A or B buttons pressed. What's my next step? Is it time to connect some speakers?
 
Uh oh. No, I set it while attached to the dim bulb. I'm assuming your question leads me to my next step of setting it connected normally.

I'll do that and report back.
 
Ok. Will try tomorrow if I get a chance. The speakers are in the garage and it's pretty chilly out there! I could try bringing them in - but they are mounted and a bit of a pain to move from their currently location. They are BA-100s - so they are a bit bulky as well.

So, I may not post for a day or so. Thanks again for the help so far. I do have capacitors ready to throw in this should it need them.
 
Good indication with the relay.. seems like somebody cranked the pots bias thinking more power. Relay not kicking in means protection circuit working. I agree very low listening and let audio path caps get reformed.

Mains caps are probably good as it powers all. Unless you have some ps related hum hopefully you won't need to replace main same caps so go for some listening.

lol drag the amp out to the garage..
 
Well, I did go out to the garage and plugged everything in. Hit the power button, pressed speaker A and then increased the volume slightly. Relay did click and glorious sound came out of the Advents!! woohoo! I didn't get to run them very long as I had a long list of other items to address, but I ran them for about 15 minutes and all sounded good. I changed balance from right to left and no crackling. Also pressed loudness button and that added nicely to the low level sound.

I'll not get to these again for a couple of weeks (they are now at the house that I'm moving to), but while I was there I grabbed my wife's Yamaha R-700. It needs help as well - different issues - so I'll start a new thread for that once I get organized. But, I'm headed to California for a few days. Catch you folks on the backside. Thanks for all your help and advice.
 
You must log in or register to reply here.
Back
Top Bottom