PL-2000 Rt Channel Issue

[vmedia]

Hello.
Ever since I acquired a 400 amp a few months ago I have been reading through threads here on WO upgrades etc, great stuff and the amp continues to get better and better. Great stuff here, thanks to all for taking the time to post your knowledge!

I now have a PL-2000 which works well, but has a right channel that sounds thin (lacks mid to low bass) in the phono stage. Sounds great on aux input. It came to me this way with some excess noise on the left channel that I solved by rebuilding the phono stage (caps and MF resistors) - along the way of course, all solder connections are now new. Cleaned all pots, rca conncections as well. (I've swapped input and output cables to confirm that the issue is in the pre-amp, specific to the right channel)

I installed sockets for the phono and ambiance circuits so I can swap around ICs (I have three 4739 - two NOS and one that came with the unit) IC changes do not affect the right channel's lack of low end.

The right channel RCA input jack was beat up (cracked, etc) so I replaced with one of the tape input jacks (looking for a replacement if anyone has a couple laying around?) Thought this would solve the issue - no luck.

Power coming to IC pins are +16 and -16, so that seems on target.

I have the schematic and service manual and don't really see any voltages to check related to the phono stage.

Any thoughts on next steps to track down this issue would be most appreciated.

 

[mlucitt]

Frequency related issues in the PL-2000 are likely a capacitor problem. Because this issue is living only in the phono section, there are only a few suspects. You can replace them all at little expense.

 

[vmedia]

Thank you for the response.
I have already replaced all components in the phono stage. However, my next step, influenced by your advice, is to swap caps from left to right to see if the problem shifts. Always possible that a new component is bad or there's an issue with installation!

 

[mlucitt]

In the PL-2000 and the PL-1000, when I am recapping I always mark the polarity of the electrolytic caps with a fine point Sharpie because the boards are not silkscreened with markings. Is it possible that a polarized cap was installed backwards?

 

[vmedia]

There are only four electrolytic caps in the phono stage and they each match the way they were previously installed as well as the schematic. (This happens to match the board markings as well.)
Electrolytic caps are C2, C9, C6, and C13. Are any of these known to be marked incorrectly on the board and schematic?

 

[mlucitt]

You have eliminated the easy solution. Not that is matters (more out of curiosity), what kind of capacitors did you use to replace the electrolytics?

 

[vmedia]

Thanks for your question. I haven't actually had a chance to swap the caps (busy week) but I have been wondering about my cap replacements. Replaced the four electrolytic caps (C2, C9, C6, C13) with Nichicon PW series. I did not have any gold (muse) caps at the proper values at the time. I would be surprised if this would cause an imbalance in low end between channels, but I am not an expert.
Thoughts?

 

[WOPL Sniffer]

Thank you for the response.
I have already replaced all components in the phono stage. However, my next step, influenced by your advice, is to swap caps from left to right to see if the problem shifts. Always possible that a new component is bad or there's an issue with installation!

Bad move...... The extra heat involved is an invitation for an early failure. NOT recommended

 

[WOPL Sniffer]

these caps cost nothing....

 

[vmedia]

Finally got back inside the 2000 and upon extremely close inspection I discovered the issue. I installed a 480 ohm resistor at position R6 instead of 460K ohm. Thanks for your help on this.
And yes, another order of parts is coming today to make sure all caps are high temp.
Next up is replacing the RCA jacks. They seem to be self-destructing due to age (beyond the obvious solder connection issue). I have not found a solid recommendation, but I've only been searching for about a month (!)
Any thoughts on the preferred method?
Thanks again.

 

[laatsch55]

Check my thread on DChristies's PL 2000.
I'm replacing all the output Jack's with Switchcraft 3501's

 

[vmedia]

Awesome thanks - I had seen that thread, so I can assume that it is ok to use jacks that do not include the internal switch (?)

 

[laatsch55]

Yes, but I would make a set of RCA shorting plugs for the phono inputs when not in use...

 

[vmedia]

Great. Thanks!

 

[laatsch55]

Welcome Sir!!

 

[vmedia]

I've been enjoying the pre-amp and am now working through a couple other issues. Of course, this comes with some more questions.
My switched power function is not working. I've pulled apart and cleaned/fixed others in the past. Is the PL-2000's power/volume switch serviceable?
Also, my unit does not have caps at C47-50. After scouring this site, AK and others, I have not seen any pics of units that are missing these components. There are jumpers (sort of) in these positions. I'm attaching a photo. Any thoughts? I would happily add some output caps if this is advisable/improves sound.
Thanks

 

[laatsch55]

There were several iterations of the PL 22 board. A complete revision list doesn't exist, so replace as is on the board you are working on......

 

[laatsch55]

The power switch depends on your level of expertise, myself, haven't tore intro one..

 

[WOPL Sniffer]

shoot me a pic of the power switch. I have several kinds.

 

[vmedia]

Got it on the output caps. Thanks.
Attached is a pic of the power switch.
Another question: I ordered Switchcraft RCAs and shoulder washers. As I understand, the negative inputs are connected to a common ground (includes Chassis) Are the shoulder washers simply to help center the RCAs and not also shield them from grounding on the chassis (of course, they are wired to ground through the pcb)