I have a amp with bad main rail caps that would play through headphones. With speakers , the increased load would distort the channels ,
even causing the DC protect to trip.
That old NAD (1978 -1998) is loaded with 26 - 46 year old caps.
My OEM Sonance 1990 amp had 2 totally failed caps (PS) , every other one was very high ESR (quite reduced performance).
OS
even causing the DC protect to trip.
That old NAD (1978 -1998) is loaded with 26 - 46 year old caps.
My OEM Sonance 1990 amp had 2 totally failed caps (PS) , every other one was very high ESR (quite reduced performance).
OS
Dear all
The E401 breaker is bad. So I will replace that. Any hints to what to replace it with (not yet strong in the search-for-parts lingo, but have an account at Farnell).
Beyond that:
I will look at the power supply. There is now no light in the green led on the front panel.
Is it more than the two large capacitors?
In addition:
I will recap clearly what I have done and how it behaves - I can a see the unclear posts I have made and that does not help you help me 🙂
The E401 breaker is bad. So I will replace that. Any hints to what to replace it with (not yet strong in the search-for-parts lingo, but have an account at Farnell).
Beyond that:
I will look at the power supply. There is now no light in the green led on the front panel.
Is it more than the two large capacitors?
In addition:
I will recap clearly what I have done and how it behaves - I can a see the unclear posts I have made and that does not help you help me 🙂
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After 30-40 years , even the led's go bad. Both my Sonance's had dim greens and failed red led's.
The 2 large ones are always "spent" (failed or close). Any auxiliary (12V , 5V - 220uF-1KuF) are usually very poor.
Even the (not yet failed) small signal NP and DC blocking caps are contributing to higher offsets and reduced performance.
Mylar/film and ceramics last forever , unless a some hard fault killed them. I upgrade amp compensation ceramics with silver mica
and look at all solder joints , especially around larger (hot) regulators and resistors.
OS
If the original state of the amp is not primary target then I would place a speaker protection module into the speaker output path - these are cheap on eBay and a relay is better than such a circuit breaker or a fuse (which is used sometimes in older cheaper amplifiers).
But it seems that you have added problems during your activities so I would recommend starting from square one:
- check the fuses;
- use DBT (dim bulb tester) to verify that there is no excess current draw;
- check the unregulated and regulated voltages;
- check DC offset at output transistors (i.e. before E401/402).
- adjust bias current. In case of problems find and repair the cause.
- start checking signal volumes from power amplifier - there seem to be many contacts in signal path so starting from preamplifier may complicate your work. Easy way would be to feed 400Hz or 1kHz signal into the input and walk the signal path with DMM in AC mode. A scope would certainly be better - do you have one?
- once bias is set and signal volumes are verified then distortion comes into the picture - lytics and contacts in signal path would be my first suspects.
Thank you all - the amp is old and no matter what needs a recap. My thought currently is to start there. Meaningful?
I am not experienced enough to find "the" fault on this one.
Also, I need some learning & experience re-capping as I want to do this on a 1300 preamp I plan to use myself.
I listed the electrolytic capacitors, planning to replace 1:1.
I am not experienced enough to find "the" fault on this one.
Also, I need some learning & experience re-capping as I want to do this on a 1300 preamp I plan to use myself.
I listed the electrolytic capacitors, planning to replace 1:1.
- In the list below, what brand/type capacitors should I go for? I just want to make it run, not play around with super high end stuff or change things.
- do I need to pay attention to temp ratings? If so on which capacitors in the list?
- Polarity? Schematic indicate most/all are polarized - does this require a special type of capacitors or are they always polar?
- Anything else I need to consider?
| Capacitor | How many? | Capacitance (µF) | Voltage | Capacitor brand/type? |
| C201, C202 | 2 | 4,7 | 50V | |
| C207, C208 | 2 | 47 | 25V | |
| C209, C210 | 2 | 220 | 10V | |
| C219, C220 | 2 | 47 | 25V | |
| C221, C222 | 2 | 220 | 10V | |
| C223, C224 | 2 | 10 | 16V | |
| C311, C312 | 2 | 47 | 10V | |
| C313, C314 | 2 | 47 | 25V | |
| C315, C316 | 2 | 100 | 10V | |
| C321, C322 | 2 | 47 | 10V | |
| C325, C326 | 2 | 0,68 | 50V | |
| C401, C402 | 2 | 10 | 16V | |
| C409, C410 | 2 | 47 | 10V | |
| C415, C416 | 2 | 1000 | 10V | |
| C427, C428 | 2 | 47 | 25V | |
| C508, C509 | 2 | 4700 | 35V | |
| C518, C519 | 2 | 47 | 50V | |
| C522 | 1 | 4,7 | 50V | |
| C523 | 1 | 22 | 50V | |
| C524 | 1 | 2,2 | 50V | |
| C525 | 1 | 47 | 50V | |
| C526 | 1 | 47 | 35V | |
| C601, C603 | 2 | 22 | 100V | |
| C801, C802, C803, C804 | 4 | 22 | 16V | |
| Total | 45 |
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Unfortunately I cannot agree with you - frequently new faults (some of them difficult to find like micro cracks in traces) are added during recap and after finishing it you may have a more complex problem to address than now.
Makes sense, thank you 🙂
I have had the transformer soaked in varnish, still hums (has been really successful on several other amps).
So this one might just be too difficult/not worth it.
Alternatively I should find someone knowledgeable locally to help me find the fault(s) and THEN recap myself.
I have had the transformer soaked in varnish, still hums (has been really successful on several other amps).
So this one might just be too difficult/not worth it.
Alternatively I should find someone knowledgeable locally to help me find the fault(s) and THEN recap myself.