28-pin DAC desoldering

Hi all,

looking to replace the stock PCM63 DAC chips in my Rotel RCD991 with the PCM63-K upgrades.

I had a go at desoldering the pins on the underside of the PCB using desolder braid, which seems to work pretty well.

However, the chip itself doesn't seem to budge to any kind of lifting when I try to prize it away. Very conscious of putting too much force into it, and am aware there may possibly be residual solder inside the joints, but am stumped as to what strategy to take.

It's quite a crowded section of the internals with several Blackgates and WIMAs surrounding the DAC chips, so I my angles of approach are somewhat limited.

Has anybody done this upgrade before, or has experience removing 28-pin ICs?

Any tips would be greatly appreciated!
 

jean-paul

Ex-Moderator
2002-09-20 7:20 am
Germany
Or cut the pins with a very sharp side cutter (a type specifically for electronics) and then desolder them one for one. In my experience (and I replaced a few!) PCM63 dies from desoldering anyway in most cases ! Forget the idea of reusing them, that will only work 100% when they would have been socketed. When desoldering pin for pin you can "pull" the pins lightly when heating them. Do this very carefully with very little force to keep the PCB tracks from peeling off. If the chip is glued that will be clear as well with this approach. I have never seen that but if so removing it with all pins detached will be easier as well.

Maybe you will want to use high quality IC sockets for the new PCM63 chips. It will guarantee easy removal for re-use in the future. I detest IC sockets for audio use but it probably is a wise idea to use them in this case. If you like the idea please buy the lowest (in height) and the best grade you can get. Maybe a stupid advice but even though the chips are bipolar I would work ESD safe with them.

* I don't know this specific Rotel (or I don't remember it ;)) but if the PCB material is sensitive you might want to use an extra pair of hands with an extra soldering tool. That way you can heat both sides of the board simultaneously and at the same time you can pull the pins carefully. The PCB won't overheat this way. You will need a friend helping out but this is worth the hassle if you like this device. Peeled off PCB tracks are nasty and need more time to repair than aforementioned way of working.

* There is probably indeed residual solder in the holes. Happens often.
 
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Thanks guys.

@Matt BH - Just bought the Chip Quik kit. Not a huge amount of space around the top side of the pins but should hopefully be able to get the iron tip in amongst it all.

@jean-paul - I don't intend on trying to keep the PCM63s 'alive' after this so will opt for the pliers as a last resort... I also have 28-pin sockets to mount the PCM63-Ks. I understand they're not the best thing for audio purity but in terms of practicality (and future-proofing) it's the best option in my opinion!

Planning on replacing the stock NE5532 and NE5534 opamps with OPA134 and OPA2134. Any other suggestions?
 

jean-paul

Ex-Moderator
2002-09-20 7:20 am
Germany
Cutting the pins really works best but let us know what you decided on. Be aware you will need a very sharp side cutter that cuts a specific way (like the small Knipex ones which are angled in a special way) if you decide on cutting. A too large cutter will put force on the pins which you don't want.

Please show the sockets you will be using. There is probably only one chance to use the right ones :) Opamps is a different issue. Better examine the schematic quite good before changing them. Again gold plated high quality sockets might be the choice for you to enable "opamp rolling". OPA134 and OPA2134 are fine devices but there might be even finer ones for this specific purpose/device.

Don't worry about PCM63-K, it is a darn good sounding old school DAC and you already have them. I am sure you can enjoy their sound. Personally I would not bother with this expensive PCM63-K and use a more modern DAC chip as they're cheaper and offer some more possibilities :D

Since the CD player is opened anyway you might want to replace the 16.9344 MHz crystal for a low jitter Tent clock module or similar.
 
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I have gold plated sockets for the opamps, and I think the DAC ones are gold too. Will double check...

I looked into newer DAC chips for this CD player but wasn't sure if there were compatibility issues. I do know however that the RCD991AE had the 'K' model, so went ahead.

Basically I'm trying to turn my 991 into a 991AE :happy1:

As a long-term plan I intend on adding a Tentlabs clock, and possibly power supply, but I'm getting the 'small' mods out of the way first.