replaced all e-caps, no joy

inkboy1

inkboy1

Bob's my uncle
hi all. i'm working on a yammy ax-550 integrated that i bought online from a guy who swore that it worked fine when he sent it. but it arrived here with a corner bashed in by fed-ex and was non-working. if i plugged in headphones and pushed in the "pure direct" button, i'd get a very faint signal at the highest volume levels, but only if i pushed in the "A" or "B" speaker button.

i replaced all electrolytic caps, but get the same results. i get no signal from any input if i don't bypass the tone board with the "pure direct" switch. there's a relay at the front that clicks and vibrates when i push in a speaker button, but there are two identical relays at the back, near the outputs, that don't react at all. they're black box-shaped relays marked DEC DH2TU 24VDC. i've cleaned the switches and pots as best i can, but no joy. what am i missing? thanks...

p.s. i've also replaced all 4 output transistors...
 
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You need to find out why it doesn't work. The first thing you should have done is measure each output coil or output transistor emitter to ground to verify 0 volts DC. It may be in protection causing no output. There may be more than one problem now because any errors made during the recap may also be present.
 
lumpy said:
There may be more than one problem now because any errors made during the recap may also be present.
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i made good joints (even used a watchmaker's eyepiece, since my eyesight is weakening), didn't have any cross-trace muckups, recap was successful, near as i can tell; it just didn't solve my problem. i'm getting 14+ millivolts dc thru the power board to the tone board. tried replacing power led, but that didn't help (read somewhere that that could cause failure in some yammy amps).
 
Just a note for future operations: Recapping is NOT a repair technique. Before recapping, complete all repairs. Once the unit is functioning correctly, then it is safe to recap. Repair operations may require replacement of one or more 'lytic caps, but that will require knowing why, and seeing the direct results.

Damage due to shipping impact will generally be found by looking for impact-related issues: fractured solder joints, broken component leads, fractured circuit boards, loose parts in sockets, broken wires, etc.

Some output may indicate that the output stage is working, but not getting input signal: missing/disconnected pre/power jumpers/switches, incorrect input selection settings, etc.

Enjoy,
Rich P
 
inkboy1 said:
hi all. i'm working on a yammy ax-550 integrated that i bought online from a guy who swore that it worked fine when he sent it. but it arrived here with a corner bashed in by fed-ex and was non-working. if i plugged in headphones and pushed in the "pure direct" button, i'd get a very faint signal at the highest volume levels, but only if i pushed in the "A" or "B" speaker button.

i replaced all electrolytic caps, but get the same results. i get no signal from any input if i don't bypass the tone board with the "pure direct" switch. there's a relay at the front that clicks and vibrates when i push in a speaker button, but there are two identical relays at the back, near the outputs, that don't react at all. they're black box-shaped relays marked DEC DH2TU 24VDC. i've cleaned the switches and pots as best i can, but no joy. what am i missing? thanks...

p.s. i've also replaced all 4 output transistors...
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First thing I would have done was made a claim to Fed-Ex for the shipping damage before going ahead with any repair or re-capping.
 
"Integrated"...... Uhh... you DID check for pre-out main-in jumpers?

I made that stupid mistake once replacing ALL the outputs on a Linn amplifier.:scratch2:

The look on my face was no doubt priceless when (after 4 hours work) I turned the amp around and looked at the labels on the back.

And then there's the tape monitor switch.....
 
Out of curiosity, I was wondering... how, what, and where would the effects of lost electrolyte be noticeable? I never really put much power to it before the swap out of the filter capacitors ((2) 80v 22,000uf in my example) but at relatively low levels I did listen to several song to get a feel for the sound and compared the sound post replacement. Difference was negligible if any. Did my "restraint" prevent me from hearing the problem or was it even necessary so long as sound was being delivered to the speakers.
 
Lost electrolyte results in component value drift, and eventual failure of the capacitor.

Industry history shows that about 1/2 of the caps that fail, fail "open". Depending on where they are located and their function in that location, there may or may not be a user-detectable malfunction (including something audible).

The other 1/2 of caps that fail, fail "short", which almost always results in circuit malfunction, including, and especially, catastrophic damage to associated circuitry.

While electrolyte is drying out, circuit performance may be adversely affected: timing circuits, frequency response circuits, interstage coupling circuits, power supply ripple and impulse capacity circuits, etc. Some caps can drift significantly, without user-detectable effects: such as in simple bypass applications.

Some 'lytic caps rupture, due to increasing internal temperatures, due to electrolyte malformation. Such caps generally blow corrosive electrolye on local circuitry and components, resulting in divers kinds of circuit, component, and chassis corrosion.

Enjoy,
Rich P
 
dspear99ca said:
Ahhhh, the old "my car wouldn't start so I replaced the heater, then the windshield wipers" method....
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nope. was planning to replace all electrolytic caps regardless, and power transistors looked like old bike patches. thanks for the raspberry, though...
 
Tinman said:
Corner bashed in? Look for a hairline crack on the boards.
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KEE-REKT!
thanks to you, avionics and others for this tip. there is a 3-inch crack in the main power board crossing several traces. (valuable lesson here for me).

can i drill tiny holes in traces on each side of crack, then bridge with, say, old cap connector clippings? anyone have success with this technique?
 
The way I fix broken traces is to scrape the solder mask off the trace with an exacto and then solder a piece of bus bar, wire or solder wick to bridge the gap.

Another method is to simply use wire but solder to other points on the net. For example, the legs of a capacitor on one side to the leg of another capacitor on the other side.

In any event, I would refrain from drilling any holes. Also figure out how you are going to reinforce the board so it doesn't flex anymore.
 
inkboy1 said:
KEE-REKT!
thanks to you, avionics and others for this tip. there is a 3-inch crack in the main power board crossing several traces. (valuable lesson here for me).

can i drill tiny holes in traces on each side of crack, then bridge with, say, old cap connector clippings? anyone have success with this technique?
Click to expand...

Just scrape off the PC board coating on each side of the crack with a exacto blade or sand paper til you have shiny copper.Tin the copper trace with solder,then jumper with a cap clipping or a small piece of solder braid.Once all traces are jumpered.Get some 2-part epoxy and fill/coat the crack with a bead of epoxy. If there is enough space you can reinforce the board by epoxying a stiffener to the board.
 

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avionic said:
Just scrape off the PC board coating on each side of the crack with a exacto blade or sand paper til you have shiny copper.Tin the copper trace with solder,then jumper with a cap clipping or a small piece of solder braid.Once all traces are jumpered.Get some 2-part epoxy and fill/coat the crack with a bead of epoxy. If there is enough space you can reinforce the board by epoxying a stiffener to the board.
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Damn! How many time have we had to do that! :thmbsp:
THANKS UPS! :D
 
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