Crown D-150A Filter Caps & Current Draw

[misterc57]

you can try HA2730, HA2735

Have not been able to find HA2730, HA2735.

I now see what g! was referring to in regards to fake parts. All of the vendors selling UA739PC ICs on eBay from outside the US have comments indicating the items are fake.

I did find these two which I need to inquire about the vendors. A bit pricey...

https://www.questcomp.com/part/4/ua7...chantcenter&ut m_term=ua739pc&gclid=cjwkcajw5p2abhaleiwaady7dnjnnlggvfb twaydoiteu1wjbfak_bu9g-dmdn1c3_mvoxkf2iawfxocd4mqavd_bwe

This one has the same top print as the one I pulled https://www.electronicsurplus.com/fa...r-preamplifier

Still wondering about alternatives that can be dropped in. I am not understanding the compatibility requirements for replacements.

I checked the output V with the IC removed. Outputs are at full rails at 44.5 VDC. Does this mean anything? If I find a replacement IC will this solve the DC output or can there be other issues?

Thank you

[g1]

There are no pin for pin compatible replacements, aside from NTE725. That means any replacement will have a different pinout, so you would have to mount it upside down, and run wires to the appropriate traces.
The other hitch is that the 739 uses external compensation, and modern op amps don't. So you would have to mess around with the compensation circuits in the crown (remove or disconnect).

Here is a guy selling the NTE sub, seems legit: https://myelectronicparts.com/shop/i...amp-ic-linear/

[x-pro]

I checked the output V with the IC removed. Outputs are at full rails at 44.5 VDC.

44.5V output of which polarity?

[misterc57]

44.5V output of which polarity?

+ 44.5 VDC measured at both speaker outputs.

[x-pro]

without the 739 it should be like this
when using the 749, but without it it would be -44V

[misterc57]

I think I found a source. This would be a direct drop in, right?

https://www.electronicsurplus.com/fa...xoCSZsQAvD_BwE

Thank you

[Delta362]

I used this for my Polytone 104 repair earlier this summer. I replaced the crusty 14 pin IC socket. The opamp on the adapter board had a bad section so I replaced the SMT opamp. The adapter board plugged right into the spot of the original RC4739 and is working well.
https://www.ebay.com/itm/283861029403

Your link looks like it would be a direct replacement. Worth a shot, I think.

[g1]

I think I found a source. This would be a direct drop in, right?

Yes, that looks good. As they are a surplus dealer you should be getting an original part.

[misterc57]

Have not order a replacement IC yet.

A new IC socket was installed. Then the old IC was checked for shorts, there were none. It was installed onto it's own new IC socket. This socket with chip, was then installed onto the new socket on the board. Continuity was checked from board to the socket and everything was good.

Powered on and still have 44 VDC offset at the two speaker outputs.

IC pin readings below are symmetrical. There should be 0 VDC at pins 6 and 8 (negative feedback), instead I see 2.1 VDC.

Also the outputs (pins 1 and 13) should be about 1.75 VDC per the schematic.

The input and output offset pots were fully rotated with no changes to the DC offset. At one point I did have zero offset on Channel A only, Channel B had 14V offset. But that did not stick and subsequent cycles repeated 44 V dc offset on both channels.

I have found no issues with the feedback circuit components, the fact that I am seeing the same numbers on both channels points me to something that would be in common to both channels.

The service manual states positive offset on both channels, defective IC or D4. D4 and D5 appear good and I am seeing approx +10 VDC and - 10 VDC respectively.

I think that leaves only the possibility that the IC is defective. Looking for confirmation or other things to check.

Thank you

[g1]

I guess you doubled up on sockets because of the broken IC legs? Did you solder those pins directly to a socket, then plug that in to the board mounted socket?
Continuity should be checked from board to actual IC pins, not to socket.

With the kind of corrosion that disintegrated those IC legs, it is still highly suspect.

[misterc57]

I guess you doubled up on sockets because of the broken IC legs? Did you solder those pins directly to a socket, then plug that in to the board mounted socket?
Continuity should be checked from board to actual IC pins, not to socket.

With the kind of corrosion that disintegrated those IC legs, it is still highly suspect.

Yes to all.

Thank you

[misterc57]

NOS IC installed. DC offset adjusted near zero and all is working well.

Thank you all!

[misterc57]

The input jacks on this amp are 1/4 phono and are prone to being a loose fit, causing cutouts in signal. Bending the contacts helped a little but they still sometime get loose due to the position and weight of the phono plug.

I would like to replace the input jacks with RCA jacks which would match the connectors from the Crown IC150 A pre-amplifier.

The current phono jacks are switched, the RCA would not be switched. I am thinking that this would be okay but wanted to get some thoughts here.

Also any recommendation on a source for good quality RCA panel mount jacks? There are some on Amazon but reviews are mixed.

Thank you