Technics RS1500 tune up/re-cap

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 don't think you can go wrong using the higher voltage rated caps as long as the uF value is the same. That said, when I set out to do the recap myself, I bought a couple boards off the Bay from a guy parting out his RS-1500. When I got them I noticed, as you have, that some of the cap values were different as was some layout. When I contacted the Tinman, he said they had several electronic revisions as the years progressed. I could send you these spare boards if you could use them, maybe to recap out of the unit, then swap in, which was my plan until I realized the project was beyond my capabilities and Tinman came to my rescue. PM me if you need them(pic attached) ....I certainly don't anymore.IMG_4647.JPG
 
Thanks so much for the generous offer Vince! I won't need to take you up on it, as I'm almost finished and all my boards look like they're in good shape.
Luckily, I found a local electronics shop that stocks fresh electrolytic caps so I can pick up the missing ones on Monday.

If it's of any help to people for people in the future, here's the list of caps that differed from the schematic (It's probably best to go through the trouble of verifying what's installed on your own boards):

3.3uF 25v bi-polar not polarized per the schematic: C113, C213

10uF 50v not 16v/25v/35v per the schematic: C193,C194,C216,C294,C221,C126,C129,C226,C227,C252,C151,C185,C109,C187,C209,C287,C285,C117,C217,C18,C19*

1uF 50v bi-polar not polarized per the schematic: C937,C938,C939

*IIRC there may have been one other 10uf 50v cap in the power supply.
 
Most of the 1uf, 3.3uf and 10uf caps are passing signals. 50v is probably what they had in bulk and makes no impact on the design since the actual operating voltages are much lower. I use 63v caps if I happen to have them as well.

Sometimes it's easier to purchase say 63v 10uf caps in large lots than 35v, and the circuit won't care. Plus, having a large stock of a more common voltage cap means you can use ONE batch in more equipment.

But use bipolars where they did. It was done for a reason, or the schematic was wrong from the beginning.

I know there are bipolars in the reel and capstan servo boards, so be careful there as well.
 
Thanks for the advice Tinman. I did take note of all the bi-polars. My Mouser order was mostly correct.

Locally, I could only find a questionable brand's 10uf 63v caps (G-Luxon; rated 105C). They are fresh stock though. If you were in my shoes, would you fit Panasonic 10uf 25v & 35v caps per the schematic? Or would you just use the G-Luxon ones throughout? The G-Luxon ones measure well in terms of capacitance and ESR.

And just out of curiosity, have you ever experimented with replacing some of the smaller value electrolytic caps with film?
 
I never use off-brand capacitors. They work, but are short lived. Stick to panasonic, nichicon, united chemi-con and vishay.

As to replacing small caps with film, I personally don't bother because I'm too old to actually hear the subtle differences nor do I have any delusions that I can. In my teens, yes. At 51....... Not so much.

Film caps are good where stability is important, and if you look at the technics you will find some in critical areas.
 
Thanks so much for the tips Tinman.

So I completed the re-cap and everything went fine. I had enough Panasonics on hand to up-rate all the 10uf 16v caps in the schematic to 25v and 25v up to 35v.

Unfortunately, re-capping didn't solve my initial problem of an uneven and weak low frequency response in repro. I wonder what would be the next things to try?
I'm surprised because I read elsewhere that these decks were supposed to have fairly mighty head bump.

Another observation (I'm not sure if this is normal on these machines), the VU meters seem to be quite inaccurate for signals under 100hz (compared to my Agilent U1252B, which is fairly accurate from 20hz to 100khz). Here's what the 'source' output looked like when fed from an oscillator:
rs1500_vu_zpsosungwfw.png


Another issue: The peaking coils aren't seemingly doing anything to adjust the high frequency EQ during the record alignment.

On the plus side, the wow and flutter seems good, the azimuth was easily adjustable and I'm getting good (but not flat) high frequency response well past 20KHz @ 15ips (the only speed I use).
 
How are you measuring repro frequency response? Which test tape (brand/model)? And what test equipment?

Can you post a plot of play response for both channels? And for both heads (2T and 4T)?

Your Vu meter response is ok and normal for that deck. It's just for setting record level and nothing else.

Record peaking coils do very little when adjusted. That is normal.
 
Hi folks, I took a long break from this but it turned out that my frequency problems were caused by dirty trim pots. After cleaning them I've been able to get very linear frequency response. Thanks again to everyone for their help. The deck runs great.
*One last thing I'd like to do is replace the VU bulbs (one is currently dead). Does anyone have a good method for getting at the VUs? The exploded drawing in the scanned manual I've found doesn't seem to offer any clues. The screw in the embedded image is very much seized so I hope that's not the only/best way in.*
-update: oops the plate was only stuck (dried grease I think) and could be wiggled free. No need to remove that circled screw. Now to find some appropriate lamps (the bi-pin style ones I have are too bulky).
31240727404_069970dd83_k.jpg
 
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If that is the only way in, the use of a low wattage soldering iron to apply heat to the head of the screw and the proper sized Phillips screwdriver may help.
 
Hi again all,
My RS-1500 has been working very well in general but I'm trying to fix one last problem:
If I stop or pause the machine near the end of a reel (ie when the takeup reel is nearly full), the machine struggles to go into play again. It either takes a moment to get up to speed or won't play at all.
Both 7" and 10" reels are equally affected. I've attempted to adjust the takeup and supply torque with both the 'simple' (voltage readings) and 'ordinary' (Tentelometer reading) methods in the manual. I've thoroughly cleaned the tape path as well.
Anyone ever experience this issue?

Update: cleaning the plungers for the tape tension guides as well as re-doing the capstan motor phase calibration (where you align the sawtooth and pulse waves) seems to help out a lot. Would anyone know if it's normal for there to be a small amount of lag coming up to full speed near the end of the tape?
 
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