THS7316 AMP Framemeister issue

[peasoup]

Hi all, I'm having a bit on an issue with some amps I put together via oshpark. Everything seems to work on a CRT and straight in to a scart input on a LCD but the framemeister just displays a black screen.

The amp:


https://www.oshpark.com/profiles/ichigobankai

I've used ths7314/6 based amps before with out any issue I wonder what the problem could be?

[Keith Courage]

Is your framemeister cable Euro scar or JP21?

[peasoup]

Thanks for the reply. Euro scart, it's all wired up correctly works ok on a duo I have.

Looking at the data sheet for the THS is shows a 75ohm on the output but these boards have a 91 out  and a 470 to ground, would that make a difference?

[peasoup]

Hmm weird, so I built a another amp and  put it in an original white PCE. On the CRT it works but it looks a bit over blown and theres weird black shadowing on some elements. Tried it on the Frameister no picture at all, no input, I bridged R10 so it was getting 5v out to see if that would make difference but I just got a black screen. Really odd.

[SignOfZeta]

Anything from Micomsoft should sync even an unamplified PCE. Something is f-ed.

Someone here recently mentioned that the OG PCE has an unbuffered output. That may be the brightness issue right there. Personally I'd never waste my time building an RGB circuit without trim pots.

[Keith Courage]

I'm not familiar with that PCB setup but here is a similar one using the same 7314 that I know works. Maybe you can compare the two and figure out what might need to be changed on yours to get it working.




Also, are you making sure to use ceramic caps except for the larger 330uf ones? That could be your problem if you are using standard caps with polarity in place of the other smaller ones.

Oh, and how is your scart Port/Jack wired up?

[NichlasEk]

i have used this design on the duo, the IFU and the super CD. all working just fine. tho i used tantalums for the bigones instead of normal electrolytics.

[peasoup]

Oh that's good to hear NichlasEk, thanks.

I have to say this is baffling me. Ok so I've made two amps both work fine on 2 different Duo-R when plugged in to a CRT but when you plug them in to an LCD or via a framemeiester, nothing. I tried the amps on a working Duo and they both worked on the framemeister, I took the working amp from the Duo and put it in an R and nothing again. Same tv same scart.

I reseated the DIN8, but no go. I  checked via composite, works fine on the framemeister. When I turn off synch I get a jittery picture so it must be something to do with comp sync?

Failing that it could be the scart lead but that works fine on the Duo with the new amps....undoubtedly it's going to be something stupid and I'll be back looking like a fool

[NichlasEk]

all i added was a 220uf on the syncline in the scart head. or else i would get syncdrops.

[peasoup]

interesting this could do the job I'll give it a try thanks!

I was thinking of making a LM1881 sync stripper circuit to see if that helps, though I've never needed to do that with Duo R before.

Edit: Tried a 220uf on the comp line didnt seem to make any difference though :/

[peasoup]

Ok thanks for the help all, got it working

Made a a synch stripper and it worked. Like I said though I've never had to use one of these circuits on a pc engine before, are there composite variances from machine to machine? I thought it might be due to the psu but that doesn't seem to be the case as I tried an official one as well.

[NightWolve]

I see, so it wants a clean H/V Composite Sync signal. You could also tap that from the chip and amplify it, the circuit would be less complex (guess you already had a LM1881 chip?) and always better to get a clean source (pin 44 on Hu6260). Some monitors can Sync from it raw, but others will require a simple amp like the classic Japanese transistor one.

[peasoup]

well I just wanted it to sync with the framemeister, after further reading I realise the LM1881 is probably overkill, not 100% what to do though.