Intermittent problems in re-capped Cambridge Audio D500SE

[tj2]

I re-capped two old Cambridge Audio D500SE cd players. One version 1.0, the other version 2.0. The main difference is that the servo mechanisms are by different manufacturers. Version 1.0 has a Sony chipset and I've forgotten who the v2.0 chipset manufacturer is. The units now both have weird intermittent problems. Both occasionally will show that a CD is playing but there's no (analog) audio out. The v2.0 worked just fine for a couple months and then started having these problems but the v1.0 unit had them immediately. With the v2.0 unit, sometimes the disc isn't recognized and is spit out again and rarely the front buttons don't work though the remote does. I've tried cleaning the contacts on connectors but that doesn't cure the problems permanently. Oddly, if I hit the power button while a disc is spinning and then restart the player it will usually work normally again for a while.

I'm guessing that one of the replacement caps is too different in ESR from the original. I used good lowish ESR Japanese caps to replace the originals. I don't have the service manual so I'm at a loss for what to check to find the source of these weird problems. Does anyone have any advice?

Ted

 

[DF96]

This advice comes too late for you, but others may benefit from it.

When re-capping is necessary (which it often isn't) change just one or two caps at a time, and then re-test for correct operation.

Only replace caps which are likely to be life-expired, or which you have measured as being life-expired, or which are expected to shortly become life-expired.

Unless you have reverse-engineered the circuit, and so understand it better than the original designer, don't be tempted to substitute 'better' components except where you are sure (on the basis of your own circuit understanding) that this will not create problems.

Don't believe everything you read on the internet, especially about tweaking audio and 'recapping'. Most of this is written by people who know less than you; the difference is that they don't know how little they know. This remains true however much or little you know yourself; you can always find someone online who knows less yet claims to know more.

I am afraid you will have to fault-find. This will be made much harder because the items have received multiple changes. Start by checking DC values.

 

[Willi Studer]

The common suspect for both overhauled units is the service guy.
I don't know your expertise level in electronic works, but I would do the following:
- check the correct polarity of every replaced capacitor
- check both new and old solder joints for dry or bad ones
- check all connectors and flat cables for proper plugging and contacts

I don't think a different ESR value would make any difference, nor give intermittent symptoms.

 

[tj2]

Thanks for the replies, DF96 and Willi Studer. I did check voltages and ripple on the supply lines and voltages are in spec and ripple is on the order of millivolts just after the regulators.

Yes, DF96, you are right about not modifying a design if you don't understand it. My intention is not to modify but rather to replace old capacitors from mediocre manufacturers with equivalents from better manufacturers. (Equivalent means same capacitance and ESR/impedance and correct voltage rating.) It is useful to have a set of data sheets for a large set of manufacturers and capacitor series. I sometimes cannot find data sheets for capacitors from some off-brand Chinese manufacturers and am loath to use the measured ESR on aging capacitors.

These are the first CD players I've re-capped but I've re-capped many many unreliable computer motherboards, routers, wi-fi access points, switching power supplies and other devices. I've been repairing electrical and mechanical devices for years and been in the habit of replacing mediocre brands of capacitors in my devices for about a decade. In my experience, good quality components make the difference between a solidly running device and one that behaves erratically. (I'm not a professional tech; I'm a physicist so it takes me some time to figure new devices out and I greatly appreciate the instruction of those who are skilled techs.) Often the caps are vented but sometimes not. This time I got worried by reading about people whose CD players had been ruined by bad filter caps after the bridge rectifier and thought it might be helpful to do this now rather than take a risk given the age of the units. Since it gets rather toasty in parts of these CD players I thought it best to replace every electrolytic and be done with it. Apparently I've jumped the gun.

I've only once damaged something while replacing capacitors--a wi-fi radio in a router/modem stopped working once, probably because my wrist strap came loose from the ground. (Other identical units I've done work fine and one has been in operation in my living room for years now. If they aren't re-capped in a timely fashion they die around the time the warranty runs out.) In only one case in my experience has a device been fairly sensitive to ESR: there's a smallish capacitor in the 5 VSB circuit of certain PC switching power supplies that needs to have a highish ESR or the circuit will not start up. (I'm also aware that the ESR of output capacitors for PNP or p-channel LDO voltage regulators must lie in a fairly narrow band in order to avoid self-oscillation, but I've never run into that on the bench.) In my D500SE units my replacement capacitors are good matches for the ESR of the originals, but there are a few where the ESR is 25-50 % of the ESR of the original capacitors but that didn't concern me initially.

 

[Extreme_Boky]

The hot spot is developing somewhere around voltage regulator IC's... this can be detected if you try to cool down suspect areas with short freeze spray burst, isolating each IC at the time. It could be a doggy zener diode as well...

Another suggestion is to track the signal from the transport while the CD player is working correctly, to learn which signals to expect and at what point. Then repeat when the CD player "mutes" the analog-out signal. This should narrow the problem down to CD mechanisms, or DAC / analog section. You will be more confident in fault finding, and you'll be able to diagnose the fault with great certainty, if you know what signals to expect around the CD player.

Also, look at the reset circuitry. This could be figured out by checking the PCB tracks around the microprocessor IC. Obtaining the circuit diagram is pretty much impossible; however, you can get the datasheet papers for each of the IC's used inside the CD player, that will explain the principles of operation.

Good luck,
Nick

 

[DF96]

In post 1 you described some of the symptoms. Consider the details; I am sure there are more. For example, the buttons sometimes fail but the remote works - that may narrow down the area of possible faults. As a physicist (like me) you will be skilled in using causality and symmetry!

Most likely you have a power supply problem; modern logic can be quite fussy about its supply rails. The other possibility is a failure of local decoupling, perhaps due to the new caps being too low in ESR.

 

[tj2]

Thanks for your suggestions Nick, DF96, and Willi Studer. I appreciate it.

Willi Studer, your suggestions are solid and are the first things I tried. I'm pretty compulsive about making excellent solder joints and I spend a good long while going over the whole of each board under the loupe, with iron at hand after working on it. My joints are usually better than factory and I rework any marginal factory solder joints.

Nick, I don't have a lot of test equipment (just a multimeter, ESR meter, and an oscilloscope) so at best I could only do a crude monitoring of signals from the transport, but checking on components near the voltage regulators is certainly feasible. It's also a good suggestion to find the data sheets for the ICs to try to work out roughly the functions of the parts of the circuit. I had thought that the ICs would be so specialized that data sheets would be impossible to find. Perhaps I was wrong; I'll get on it.

DF96, yes, I've been trying to piece together the symptoms, which led me to suspect faulty contacts caused by disconnecting and reconnecting the connectors or improper power caused by a too low ESR of some of the replacement capacitors but, since I don't have a schematic, there could be some other problem, perhaps the reset circuitry as Nick suggests. I first tried cleaning and tightening the board connector plug contacts and I thought that that had fixed things but eventually the problems returned, which then suggests the capacitors. (In my experience the most unreliable parts of any device are contacts first and electrolytics second, but in this case there is more reason to suspect the capacitors.) It does seem to me now that it's likely that the problem lies with the operation of the servo board logic because shutting things off while a disc is playing tends to right whatever's wrong for a while. It's as if some bit isn't getting set correctly on power-up.

I think that I'm going to look for data sheets for the servo board ICs next. The v2.0 unit is playing flawlessly as I'm listening to it right now, so it'll be a bit before I take it apart again to get those part numbers but the v1.0 unit is apart at work, so I can start there. A schematic sure would be helpful, but I saw that others have asked on the forum and not gotten a response. (In 1983 while in grad school I fixed my Kenwood TS 530S rig and all I had was the schematic, a VOM, and a soldering iron--and a nearby Dow Radio parts store. It would have been far harder without the schematic!)