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Powerdoc

Dead HR-772: Capacitor and general help please

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You're right, the diameter is the key.  What I may do is remove the old caps and see if I can just lay the cans on their side and run leads to the board.  No suppliers seem to have any that are smaller than 35mm and the originals are just slightly more than 25mm.  If anyone has other ideas just let me know.  I'm not such a purist that I'd object to ideas other than the original orientation; I just want sound.  Even looked at 10k caps, which I may use anyway just for some extra oomph.

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These are the smallest in diameter I have found so far @30mm. I don't know if you have 5mm to spare in between and 2.5 mm around the outside edge. 

 

Digit-key electronics. But I do not know the quality of this brand.

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IMG_5122.JPG

Edited by Rob
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24 minutes ago, johnrotten said:

Minimum order 200, zero on hand with 16 week lead time. 🙁

 

I didn't see that. Sorry. But maybe can use the part number and find somewhere else.

Edited by Rob
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10 hours ago, Powerdoc said:

What I may do is remove the old caps and see if I can just lay the cans on their side and run leads to the board.

35mm diameter was the smallest I could find as well.

 

https://www.mouser.com/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/Aluminum-Electrolytic-Capacitors-Snap-In/_/N-75hr0Z1yzvvqx?P=1z0wqsnZ1z0j7ksZ1yx4attZ1z0vhz5&FS=True

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6 hours ago, johnrotten said:

Minimum order 200, zero on hand with 16 week lead time. 🙁

Just ordered 2 35mm wide ones and I'll lay them on the side tie them together and run leads to the board......hopefully.  They arrive on Wednesday.  Thanks

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I have three of these units, as the hearts of three different systems, and have encountered a variety of problems over the years, though overall they are quite reliable. In fact, it's a few years since I had to deal with any 772 difficulties.

I see references here to “the” power supply. Actually there are quite a few secondary power sources, and they all have to work or you will have problems. Assuming all your fuses are intact, check soldering at each little heat sink – those little regulators run quite hot, and solder failure results. Associated transistors could be blown, and/or resistors fried. Maybe start with Q941 on the +15v supply.

 

RobertR

Edited by RobertR
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RobertR:  Thanks for the information.  I saw one of your prior posts that referred to a resistor which I checked and it was ok.  Will see what happens with the new filter caps.

 

Can the power modules be checked for shorts in circuit? Thanks!

 

One thing about the power regulators-at least they have some sort of heat sink.  I have some other equipment that was "audiophile" quality that don't and the circuit board traces to them have actually lifted off the board.  I'm going to add a stick-on sink to each one of the ones on the 772

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Edited by Powerdoc
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I'm assuming you have the schematic and can read it. If not, you'd be best advised to get some first-hand help.

 

The regulators, such as the one I mentioned, test like any bipolar silicon transistor. That one is a 2SD1682 – 2.5 amps, 60 watts, high speed. Last I knew that number was NLA, but the 2SD1683 was, and it works fine, except the pinout is backwards, making installation a bit inconvenient, what with the heat sink to deal with. The heat sink won't even begin to fit turned around 180o, so one must extend and insulate the outer transistor leads, and carefully criss-cross them.

 

If I were working on it I would figure out why it's dead before recapping everything – what if you make even a single mistake? Then you'd have maybe two problems, or worse.

Find the test points for those power sources, plug it in, turn it on, and check those voltages. Something is missing, and it doesn't have to be capacitor related.

 

RR

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Well, it's I again.  Got the new 8200/80 caps, installed them (one is soldered into the PCB directly and the other is zip-tied upside down to it and connected to the PCB by 18ga wire.  Plugged it in again and nothing new:  Screen is blank and it goes into protection in about 7 seconds.  Measured the voltage at the new 8200 caps and it's 71v (not much leeway from the 80v rating).  All fuses are intact.  Looking at the PCB with stronger glasses (now up to 4x power) I see a couple more questionable caps with some ? leakage on the board and I'm going to go to the schematic and see if they would make any power difference.  Some corrosion around a couple of resistors made it impossible to measure so I may just go ahead and replace those too.  I need the practice soldering.  As RobertR has suggested I'm going to look at the VR's.  Will make effort to see where the display gets its power and work from there.  I feel certain I'll learn a lot more about electronics and electronic diagnosis before this is all over.  Not that I really NEED another piece of operating audio equipment.

Edited by Powerdoc
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The enemy of good is better....Last night, after re-soldering a couple of questionable solder joints voila it didn't go to protect and the speaker relays were working.  Still no display.  I looked at the board and some more caps looked somewhat suspect so I got some new ones today, inserted them and it's going into protect again. (emoji:  hit myself in the head).  I checked my work, twice, made sure the caps were oriented +/- correctly and that there was a proper capacitance tested in circuit.  I'm perplexed!  In any case I hope that the IC601 which drives the readout isn't bad as it isn't available apparently.  Picture shows the large filter caps which had to be McGyver'd to get them to fit.  Yes I know the exposed lugs are a safety hazard and that will be protected IF I CAN EVER GET THIS TO WORK!  All the black caps have been replaced.  The saga continues!

imageedit_16_8432009746.thumb.jpg.a33d842661def96173c8fc88aac6eb3b.jpg

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Far more likely than IC601 being defective is that it, or something else, is not getting power. I'd do some voltage checks. Even if it only runs for 5 seconds you should find DC voltages on the main board as follows:

 

Positive end of C941 = +15 v, measured to chassis ground

Negative end of C942 = -15v           ''

Positive end of C947 = +13 v          ''

Positive end of C954 = +6 v            ''

Negative end of C951 = -27 v         ''

 

Lack any of these voltages might cause the unit to not lock on. They don't have to be exact, just ballpark.

If one is missing, we have to work backwards to see where it got lost. Besides caps it could be one of the three 'R's – rectifiers, resistors, regulators.

 

 

Don't worry about those voltage ratings on the big caps – it can run at over 80v, even, and the effect will just be slightly less capacitance.

RR

Edited by RobertR
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thanks; getting to the voltages again tomorrow; was wondering if constant recycling of the standby button to get it to turn on was a problem; still can't figure out why it transiently stopped going into protection. C954 was one that I replaced.

 

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I gave you cap numbers only for ease in your finding the places to check, not because I'm convinced they're the only problem.  The one you mention is on the emitter of Q947, which powers a bunch of stuff on the microcomputer/display board.

RR

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Quote

 

Thanks again!  I'm going to go through my changes today again possibly to dismount/remount the caps and the 1 resistor I changed.  Bugs me that I'm going backwards here!  I may reprint the manual I have, for the schematic pages, on 11x17 paper just to make following the traces easier. 

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Put a few layers of insulation tape on that large cap, flip it over and shorten those leads. Rotate it to sit in its original position before you tighten the tie wraps in case you need to access any of the components it is currently covering.

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Thanks B-Man.  The problem with rotating it is that the diameter is 35mm and it interferes with the capacitors near it.  I have it rotated so as to interfere with the least neighboring components.  

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