CurtPalme.com Home Theater Forum

**Curt Palme** · Posted: Fri Jun 14, 2013 2:19 pm Post subject: Oddball reel to reel problem

Thought I'd post this for all to read, not that anyone will ever run into this ever again... Smile

Still, it's one I need assistance on, but I'll be able to figure it out later today...

I got in a pro machine, a Fostex G24 reel to reel. 1", 24 track, 15 IPS only. It has 24 individual cards for the R/P playback. Each card had massive amounts of bad SMT caps, leaking all from the bottom of the caps onto the PC board. We're talking literally 500 or more caps that I pulled off the boards. I posted about this a while back, and I put up some pix I think.

It took the customer 2 months to pick up the machine, only to have him call saying that the machine wasn't repaired right.

Turns out that his tape was shedding, but shedding not oxide, but some kind of coating, within 30 seconds of hitting 'play' It would muffle the sound on each track. So once I baked his tape overnight, that cured that. I also however discovered that 2 out of the 10 channels I'd repaired (that's all he wanted to pay for) weren't erasing the tape properly. THe erase function on those channels would cut the old recording down by about 20db, and simply record over the top of the partially erased recording.

Now, I've never had this happen before. I know some of the erase oscillator is used by the record head as well. The question is (Mac?): Do I need to troubleshoot the erase head circuit, or the one surrounding the record head for the partial erase issue?

I'm digging out the scope today to scope the difference between a working and a defective channel. This shouldn't be too hard to repair, but I now know better than to ever try and repair one of these decks with leaking caps again. I charged him $1000, $100 per channel, but with a cost of $300+ in good quality caps, I'm now into this deck at over 20 hours...

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

I guess I can only give a generalized opinion since I don't have any documents to look over, lol.

Basing this opinion off other tape devices I've worked on, the erase head should be doing a full erase. Any extra erase feature on the record head would probably be just to clean up any "occasional" missed pieces. I wouldn't think they would design it to have to rely on this secondary erase function. I would be looking at the main erase circuit and/or even the erase head itself. Or also, there may be some build up on the head that your basic cleaning is not getting off. How hard is it to just swap a head and try?

**Curt Palme** · Posted: Fri Jun 14, 2013 3:37 pm Post subject:

It's a 24 track 1" head. I have no spares. I did however swap the R/P cards, and it's definitely isolated to the cards. I know I was frustrated as hell last night after working on the deck for the day, so I wanted to do some 'quick fixes' to get the bad cards going. Today my head is clear again, and I will take a more logical approach to the deck. My goal is to get it going fully by noon, and I might even try to get another card or two running.

Will attack the erase function within the hour...

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Good to see the card swap verified the problem location. That's more then half the battle.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Ha, you made me look in the manual and I can now see my posts made no sense. Laughing

Told you it was an opinion without documents. Very Happy

So your on the R/P amp board? I only skimmed the manual so far.

**Curt Palme** · Posted: Fri Jun 14, 2013 4:21 pm Post subject:

My main thing was whether to look at the erase circuit, and you covered that. Time to go hit a PC board or three...

macgyver655 · Joined: 22 Aug 2007 Posts: 8508