Technics RS1500 tune up/re-cap

E

ethervalve

New Member
Hi folks.
I recently acquired a Technics RS1500US deck. It's working pretty well but I've encountered an issue where there's dissimilar low frequency response across channels (after setting the azimuth and electronically aligning the playback level and EQ settings for both channels with an MRL tape so that the high-end and mid response is about equal).
My best guess is that some electrolytics are out of spec.
Does anyone out there agree or disagree?
Also, just wondering if anyone has any guidelines for re-capping these machines (i.e. which caps typically ought to be replaced).
Thanks!
 
Recapping tape decks seems to be a little controversial. It is certainly possible that a either a coupling cap or a cap inside of your EQ circuitry has drifted substantially.

My recommendation would be to try to identify the cap which has drifted, and replace only it. See if that fixes your problem. If it does, then feel free to recap the machine (very carefully). If it doesn't, find your next most likely candidate, test/replace it. And so on.

But I would not blanket replace caps until you first resolve your problem, because it may well have nothing to do with your caps.
 
Most every one of these machines has cap issues by now. The electrolytics on these decks are much like ReVox on how they age. Also, the brakes are another age related issue with RS 1500US line machines. Not unusual to find a lot of out of spec electrolytics in one. The last RS 1500US I serviced at work, had to have all of them replaced and the brake bands done and alignment of the electronics checked.
 
Thanks for tips folks!
I'm definitely not a fan of the mindless shotgunning of capacitors approach. But unfortunately I don't have an ESR meter, so I was hoping to do some targeted replacements based on other people's experiences (since it's a pretty popular machine with a lot of examples still in use).
Kent, were you able to get the low frequency response well-matched after servicing? Unlike the Otari MX5050 (which I believe uses the same heads), I don't see any provision for electronically adjusting the low frequency response.
Also: have you or anyone else noticed if the 'simple' voltage measurement method in the service manual for setting takeup and supply tensions works adequately well. I'm having a hard time getting a tentolometer reading (tight space for measuring).
 
My machine at work I serviced after recapping and brakes had a full electronic alignment and rebiased for BASF SM 911. So, this RS 1500US has good low end response as well as measured within 1 db from 20-20,000 hertz. Tension was good on my example.
 
Well, I was very surprised when checking caps on an older Marantz Tuner that the ELNA caps were still good. I would have thought they would have been high at that point.

I also have the 1500, and it plays fine for me. Too deaf to hear any real problems anyhow. LOL.
 
Possible problem areas would be the Speed Selector switch as well as the Record EQ capacitors.
 
Belated thanks for the other tips.
So I've finally had the time to order a full set of electrolytics. In theory, I don't really like the idea of shotgun replacing them but it looks like quite a pain to access the circuit boards compared the Otari, Tascam, and Studer machines I'm more familiar with. So I'd prefer to do a little preventative maintenance in this case.
Before I get started, I just wanted to see if anyone else has experienced this transport issue:
-When I click 'stop', the tape falls away and the tension goes too low to re-engage 'play'. I have to manually spin the reels to get the tension back up. I've tried both the 'simple' (voltage setting) and 'advanced' (tension gauge) approaches to setting the tensions from the service manual but neither seems to help. Is this a sign of brake failure?
 
This is not aimed at the OP.... But for general information.

I think the most prudent thing to do is to ignore dozens and dozens of threads explaining this machine and it's purely age related problems and spend weeks over analyzing things before finally just doing what has been recommended over and over again to solve the problem.

Yes, the bloody brakes need re-lining. Yes, the caps need replacing. Yes, it's true that not all of them are bad, but it's enough of a PITA to do the bad ones, you may as well do all while in the process. Caps are cheap, time and labor isn't. Do it ONCE. The more often you tear into something to do incremental repairs, the more likely you make a mistake.

In the meantime, making all sorts of adjustments will gain you nothing. And they will now be wrong once the actual fault is fixed.

But please, keep trying to rationalize why a 30 year old deck shouldn't need any major service to run CORRECTLY.
 
Hey I appreciate the frank advice. I'll be doing the full overhaul.
Being familiar with these decks, just wondering if you've ever encountered any specimens where the bias; record level; and record EQ trimmers were brought out to a more accessible location (like the front panel)? I'm thinking of at least drilling some holes in the bottom for easier access (I'm planning on using this as a mixdown deck to along with MX5050 BII).
 
Hi all,
I'm finally tackling this project. Beginning with the power supply board, I've noticed a couple discrepancies between the schematic and the actual board.
C651 (brake drive) was fitted with a 10uf 50v cap but the schematic calls for 33uf 16v (and the board layout in the manual shows 10uf 16v).
C613 was unpopulated on my deck but the schematic called for 10uf35v.
Since this is the first board, I suspect I'll encounter more discrepancies along the way. Just wondering how you folk navigated this?
 
ethervalve said:
Hi all,
I'm finally tackling this project. Beginning with the power supply board, I've noticed a couple discrepancies between the schematic and the actual board.
C651 (brake drive) was fitted with a 10uf 50v cap but the schematic calls for 33uf 16v (and the board layout in the manual shows 10uf 16v).
C613 was unpopulated on my deck but the schematic called for 10uf35v.
Since this is the first board, I suspect I'll encounter more discrepancies along the way. Just wondering how you folk navigated this?
Click to expand...
Has the deck ever been services? If not, I would do the following;
1) Search the 'net for service bulletins using your serial number.
2) Replace the caps with a higher voltage rating (more protection) while using the same uF value.
 
As far as I can tell it's never been serviced (the solder all looks factory stock). But I can't be sure. Unfortunately the original owner (a radio jingle composer) passed away and I bought the machine off his .
Great idea about looking for service bulletins. So far I haven't encountered any on the internet. I'll take your advice and go with the higher voltage rating. I wish I'd cross referenced the actual circuit boards before placing an order to Mouser (I went by the schematics).
 
You will see green legs on the leaky caps. My RS-1500US had it on a few and although the deck was working fine, I had Tinman do a full recap and service. The thing runs as if brand new now, very responsive and sounds amazing. Unreal how good this model really is and it is totally worth putting time or money into. Good luck!

PS. I could send you my set of old caps if you want to do an inventory and get a list together, or ask Tinman- he's probably ordered a dozen sets by now.
 
Tinman said:
This is not aimed at the OP.... But for general information.

I think the most prudent thing to do is to ignore dozens and dozens of threads explaining this machine and it's purely age related problems and spend weeks over analyzing things before finally just doing what has been recommended over and over again to solve the problem.

Yes, the bloody brakes need re-lining. Yes, the caps need replacing. Yes, it's true that not all of them are bad, but it's enough of a PITA to do the bad ones, you may as well do all while in the process. Caps are cheap, time and labor isn't. Do it ONCE. The more often you tear into something to do incremental repairs, the more likely you make a mistake.

In the meantime, making all sorts of adjustments will gain you nothing. And they will now be wrong once the actual fault is fixed.

But please, keep trying to rationalize why a 30 year old deck shouldn't need any major service to run CORRECTLY.
Click to expand...


Tinman said it all. These machines need love as they are aging. And proper servicing. Since this machine is harder to service than many on those capacitors, I'd much rather replace them once, than to have this machine apart 3 or 4 times. It's an age related maintenance item as are the brakes. Service it once correctly, and enjoy it for a long time without trouble. Shortcuts cost you more money, more time, and more downtime. Do it once, right. You'll be happy you did this.
 
Hi Vince,
I'm glad to hear your deck is working well for you.
It'd be great if I could cross reference your list.
If it's of any use to anybody, I've attached the electrolytic cap list I made in Excel (based on the service manual). It rejected the xls file format so I had to upload it as a pdf.
So far I've only encountered one cap with the fuzzy green leads. It tested ok in terms of both capacitance and ESR. One of these days I'd like to build a leakage tester like the one described here: http://www.angelfire.com/electronic/funwithtubes/Testing_caps.html
I suspect the green-leaded caps would fail the leakage test.
 

Attachments

  • technics rs1500 parts Sheet1.pdf
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Here's what I have in the "removed" file (assuming none fell off the workbench):
2200uF= Qty 1 @ 25V, 1@35V, 1@50V
330uF= 1@25V, 1@10V, 4@6.3V
220uF= 1@25V, 2@6.3V
100uF=5@25V, 1@16V, 8@10V
47uF=1@50V, 1@35V, 1@25V, 1@10V
33uF= 20@16V (Note - this group had the most leaky caps)
10uF=21@25V, 34@16V
4.7uF= 4 @ 25V
3.3uF=5@25V
2.2uF=1@50V
1uF = 11@50V
0.33uF= 1 @ 50V
0.22uF= 3@50V
0.1=2@50V

I believe mine were all replaced with Nichicon
 

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    cap1.JPG
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  • cap2.JPG
    cap2.JPG
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Last edited:
Hmmm I'm seeing a lot of 10uf 50v caps on the circuit board where the schematic spec'd as low as 16v. I wonder if this was just a case of Panasonic having them on hand? Or are there maybe different revisions? It's interesting that Vince's deck seems to have had the 10uf caps with voltage ratings in the schematic.
I also ran into a pair of 3.3uf 25v caps (C113, C213) that were polarized the schematic but bipolar on the board. In the schematic, the positive lead connects to the gate of a FET (TR104, TR204).

And for the record, I'm seeing lots leaky of caps with green fuzzy leads on the main amp PCB! Really hope this helps get the low frequency response back to spec.
Also, cork pieces for the brake pads worked wonders on the transport (instantly fixed the issue where the tape would slacken after stopping).
 
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