Tascam MS-16 EQ caps on Rec Board

man-bot said:
No extender card - I could fab one I'm sure.

No pink noise generator - but I'm sure I could run one off a computer and feed it into the MS-16 so no issue there.

I do have a scope meter - Fluke 123.
Click to expand...

You may need to fab that extender card or even a set of extender cables.

If you can get your hands on some sort of audio generator software it would help.

Fluke 123, nice. Okay.

So we know recorded signal is getting to tape full-spectrum. We know that audio reproduced from tape (from either the repro or sync heads, correct?) is vastly diminished below 300Hz. Question (and maybe you answered this already): what happens if you monitor a full-spectrum input at the output (source set to "INPUT")? Is it diminished below 300Hz?

Just out of curiosity, what led you to change out C14 and the R203 (Repro EQ Low) pot? Just curious.
 
Reply - sorry was away for business for the last 4 days and haven't had a chance to get back at this.

I changed out R203 and C14 as I figured they were in the circuit around where the low issue may be... just a random approach. When I had a previous issue with range a tech I was speaking with suggested changing out the pot... regardless no dice!
 
My friends' MS-16 seems to have the identical issue on one card. I was over with my MRL last weekend. I was able to get flat repro and synch response on the card for 1kHz, 10kHz and 16kHz but 100Hz was non-existent. The issue followed the card in their case too. I'll be sure to let you know if they crack the case.
 
I'd love it if somebody could feed 100Hz tone to a misbehaving channel, set the deck to monitor input, and tell me if the tone is present at the output?

I'm trying to crack the case, but I need some help. :)

Since full-spectrum audio is making it to tape, that takes that chunk of the circuit off the suspect list as well as the input buffer amp. It's on the output side but if you can monitor a 100Hz input and hear it at the output, that will help to narrow the search.
 
Sorry - been knocked out with the flu the past few days. Ran 100hz through the channel with input selected and there is no roll off.
 
Okay. So you get solid 100Hz response throughput when you are monitoring the input?

[EDIT]

Hope you're feeling better.
 
Yep - all good when monitoring input. No frequency issues. Records fine without frequency issues. Only in playback through both repro and sync is there the roll off.
 
So the problem, I believe, is somewhere in your reproduce amp...its circled in the attached marked up schematic.

Ideally what would happen at this point is you would mount a faulty amp card on an extender card, reproduce 100Hz tone from tape through the card and start probing with your scope from the output of the repro amp and move upstream and see where you pick up the tone. That's where the fault is. That is the thing to do. If you want to shotgun something try replacing C9. But to really hone in on the problem, scoping the circuit while reproducing LF tone is the quickest way to find the bad part.

Let me know how I can help...sorry the attachment is sideways... :drunk:

View attachment Tascam 58 rec-play amp schematic.pdf
 
Sweetbeats for the win! C9 changed out and full audio spectrum back!

Thank you so much for your help!!!!
 
Hah!

That's excellent! :D

I'm glad it was that simple. Why did I put C9 on the prime suspect list? That cap is in the feedback loop of that last amp stage in the reproduce amp. Electrolytic caps can be used as simple high-pass filters in the audio path. The larger the capacitance, the lower the roll-off frequency. Typically, as electrolytic caps age, the electrolyte dries out. That results in a decrease in capacitance, which does what? Raises the roll-off frequency. anyway, again, so glad I could help!
 
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