ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
I have an old Beomaster 3000 with a cracked TR10 in the tuner section. I'm just getting static, no stations and no voltage on the collector of TR10 (which is supposed to read 27v).
Can anybody tell me what TR10 is? i am having a hard time reading mine due to a nice crack through the thing. Looks like BCx12B where "x" is unreadable. Should be the same as TR17 which is impossible to read without removing.
Any help much appreciated. Looking for a modern replacement.
A transistor doesn't just crack without a reason.Have you checked the zenerdiode at the collector?
Martin
Hi Martin-
I replaced both zener diodes in the neighborhood (137 and 138). I didn't test the old ones, just replaced them. Hoping that a PNP BC212B is an appropriate replacement for TR10.
Jeff
Tried a BC212B for TR10 and that did the trick. I have FM working again. i understand that i need to put some heat paste goo on the zener diode to keep it in tune so i'll go get some CPU heat sink paste. Looks like the "on" light bulb and the tuning light bulbs are burned out and it has the original orange capacitors so probably time to replace a bunch of parts to get it working like new again.
Don't use the fancy modern grey heat sink paste - it dries and hardens in weeks.Use the good old white stuff.
A servicekit is available, containing new radial and axial capacitors, tantals, trimmers and lamps.
Thanks Martin, I bought your service kit (and a couple of the tuning dial covers), and it arrived a couple of day ago.. I didn't think you ever needed to replace the tantalums so i was surprised they were in the kit.
Best, Jeff
Yes tantalums are different so I would not replace with aluminum electrolytic but would be interested if anyone else has opinions on the matter, Also they do not seem to drift in my experience, I would think to replace them with aluminum electrolytic would just be causing a problem for the future with no benefit?
Discussions about tantals are still going on and I get emails about the subject almost weekly, so please let mecopy and paste a previous post of mine:
Tantalum capacitors (tantals) were - and stil are - relatively expensive components, but they werechosen for a reason, - not because a capacitor was needed and some tantals just happened to be in the drawer.Tantals have certain pros over aluminium capacitors, that really shouldn't be ignored;Tantals have much less leakage.Tantals have a much better temperature stability (10-20 times that of an aluminium electrolytic cap).Tantals have a much lower ESR (10 times or more). The lower ESR also means that they havea better volumetric efficiency, i.e you can, popularly speaking, "fit a 1uF tantal where you would otherwisehave put a 10uF aluminium cap". (Of course it's not like that in all cases in reality and calculations will decidethe capacity needed, - but it helps to give an idea of the quality levels of the components).Tantals are much less noisy. They don't give the same "burst" of noise when charging and discharging begins, that aluminium caps do.In short, tantals are more "perfect" capacitors than aluminium caps. This makes them the superb choice for some circuits. - And less attractive for other.Generally speaking, tantals are the best choice for audio and video circuits, filtering, preamplifiers,tonecontrols etc. = the finer workings.Similarly aluminium caps should be chosen for power supplies and the likes = the rough and tough workings.It should be said though, that due to their very low ESR, tantals shouldn't be used in circuits witha healthy amount of feedback (unless taken into consideration of course).Keep them away from audio output stages etc. Use standard aluminium caps here (non-low-ESR is fine).If you fit f.e. a 10uF 63V aluminium capacitor in a circuit where it will only ever see a few volts - likecoupling capacitors in a typical preamplifier circuit, it will not be excited and it will diefaster than if it was used up closer to its rating, even if only occasionally.You could say that aluminium caps can "die from boredom".Tantals generally don't show the same tendency, they will last longer even if not excited andthey typically have a lower voltage rating too, so it's not at all as much of a problem.Early Beocord 6-8000s (a.o.) is a great example, where aluminium capacitors with a too high voltage rating wereused in the signal paths in some production units. Lower voltage rating aluminium capacitors were then fittedinstead but tantals would've been the better choice here, really.But nothing will last forever and tantals are no exception, they will eventually go bad and Iwouldn't expect any and all of the ones fitted up through the 1960s and 1970s to still beworking today, though surprisingly many will be found showing no signs of aging.In 1960s and 1970s B&O units, a typical pattern seems to be that the tantals are either still all good or all marginal.In other words, if one tantal is found bad - you might as well replace the lot.When repairing and restoring, it's a good general handrule to use tantals where the designers used tantals.They were chosen and paid for for a reason.